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Document and Entity Information - shares	6 Months Ended
Jun. 30, 2019	Aug. 02, 2019
Document and Entity Information
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Jun. 30, 2019
Entity File Number	001-37625
Entity Registrant Name	Voyager Therapeutics, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	46-3003182
Entity Address, Address Line One	75 Sidney Street
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02139
City Area Code	857
Local Phone Number	259-5340
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Central Index Key	0001640266
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Title of 12(b) Security	Common Stock, $0.001 par value
Trading Symbol	VYGR
Security Exchange Name	NASDAQ
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		36,933,937
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 79,885	$ 46,859
Marketable securities, current	247,577	108,947
Collaboration receivable	8,242
Unbilled accounts receivable	1,821
Prepaid expenses and other current assets	3,250	6,675
Total current assets	340,775	162,481
Property and equipment, net	14,493	12,771
Deposits and other non-current assets	2,003	1,149
Operating lease, right-of-use asset	30,041
Marketable securities, non-current	1,280	628
Total assets	388,592	177,029
Current liabilities:
Accounts payable	2,230	1,038
Accrued expenses	11,782	9,788
Other current liabilities	2,843
Deferred revenue, current portion	52,291	20,847
Total current liabilities	69,146	31,673
Deferred revenue, non-current	167,436	92,199
Other non-current liabilities	33,606	6,711
Total liabilities	270,188	130,583
Commitments and contingencies (see note 8)
Stockholders' equity:
Preferred stock $0.001 par value: 5,000,000 shares authorized at June 30, 2019 and December 31, 2018; no shares issued and outstanding at June 30, 2019 and December 31, 2018
Common stock, $0.001 par value: 120,000,000 shares authorized at June 30, 2019 and December 31, 2018; 36,677,608 and 32,364,895 shares issued and outstanding at June 30, 2019 and December 31, 2018, respectively	37	32
Additional paid-in capital	403,334	315,598
Accumulated other comprehensive income (loss)	101	(133)
Accumulated deficit	(285,068)	(269,051)
Total stockholders' equity	118,404	46,446
Total liabilities and stockholders' equity	$ 388,592	$ 177,029

Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Collaboration revenue	$ 46,087	$ 2,575	$ 51,284	$ 3,517
Operating expenses:
Research and development	28,576	16,507	53,407	31,360
General and administrative	8,322	11,762	17,981	18,945
Total operating expenses	36,898	28,269	71,388	50,305
Operating income (loss)	9,189	(25,694)	(20,104)	(46,788)
Other income:
Interest income	2,097	870	3,242	1,458
Other (expense) income, net	(133)	(717)	845	(318)
Total other income	1,964	153	4,087	1,140
Income (loss) before income taxes	11,153	(25,541)	(16,017)	(45,648)
Income tax benefit				180
Net income (loss)	11,153	(25,541)	(16,017)	(45,468)
Other comprehensive income
Net unrealized gain on available-for-sale securities	176	37	234	42
Total other comprehensive income	176	37	234	162
Comprehensive income (loss)	$ 11,329	$ (25,504)	$ (15,783)	$ (45,306)
Net income (loss) per share, basic	$ 0.30	$ (0.80)	$ (0.46)	$ (1.43)
Net income (loss) per share, diluted	$ 0.29	$ (0.80)	$ (0.46)	$ (1.43)
Weighted-average common shares outstanding, basic	36,610,918	31,976,922	34,990,989	31,868,995
Weighted-average common shares outstanding, diluted	37,941,257	31,976,922	34,990,989	31,868,995
ASU 2016-01
Other comprehensive income
Cumulative effect adjustment resulting from ASU No. 2016-01				$ 120

Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Total
Stockholders' Equity, Beginning Balance at Dec. 31, 2017	$ 32	$ 295,019	$ (287)	$ (160,713)	$ 134,051
Shares, Outstanding, Beginning Balance at Dec. 31, 2017	31,572,044
Vesting of restricted stock		3			3
Vesting of restricted stock (in shares)	145,829
Exercises of vested stock options		1,412			1,412
Exercises of vested stock options (in shares)	132,733
Issuance of common stock under ESPP		418			418
Issuance of common stock under ESPP (in shares)	38,392
Stock based compensation expense		2,260			2,260
Life-to-date cumulative catchup on equity securities			120		120
Unrealized gain on available for-sale securities, net of tax			5		5
Impact of adopting new accounting standards \| ASU 2014-09				(20,050)	(20,050)
Net loss				(19,926)	(19,926)
Stockholders' Equity, Ending Balance at Mar. 31, 2018	$ 32	299,112	(162)	(200,689)	98,293
Shares, Outstanding, Ending Balance at Mar. 31, 2018	31,888,998
Stockholders' Equity, Beginning Balance at Dec. 31, 2017	$ 32	295,019	(287)	(160,713)	134,051
Shares, Outstanding, Beginning Balance at Dec. 31, 2017	31,572,044
Unrealized gain on available for-sale securities, net of tax					42
Impact of adopting new accounting standards \| ASU 2016-01					120
Impact of adopting new accounting standards \| ASU 2014-09					(20,050)
Net loss					(45,468)
Stockholders' Equity, Ending Balance at Jun. 30, 2018	$ 32	308,296	(125)	(226,230)	81,973
Shares, Outstanding, Ending Balance at Jun. 30, 2018	32,063,948
Stockholders' Equity, Beginning Balance at Mar. 31, 2018	$ 32	299,112	(162)	(200,689)	98,293
Shares, Outstanding, Beginning Balance at Mar. 31, 2018	31,888,998
Vesting of restricted stock		3			3
Vesting of restricted stock (in shares)	61,632
Exercises of vested stock options		1,116			1,116
Exercises of vested stock options (in shares)	113,318
Stock based compensation expense		8,065			8,065
Unrealized gain on available for-sale securities, net of tax			37		37
Net loss				(25,541)	(25,541)
Stockholders' Equity, Ending Balance at Jun. 30, 2018	$ 32	308,296	(125)	(226,230)	81,973
Shares, Outstanding, Ending Balance at Jun. 30, 2018	32,063,948
Stockholders' Equity, Beginning Balance at Dec. 31, 2018	$ 32	315,598	(133)	(269,051)	46,446
Shares, Outstanding, Beginning Balance at Dec. 31, 2018	32,364,895
Exercises of vested stock options	$ 1	283			284
Exercises of vested stock options (in shares)	31,360
Issuance of common stock in connection with Neurocrine Collaboration Agreement	$ 4	77,613			77,617
Issuance of common stock in connection with Neurocrine Collaboration Agreement (in shares)	4,179,728
Stock based compensation expense		3,459			3,459
Unrealized gain on available for-sale securities, net of tax			58		58
Net loss				(27,170)	(27,170)
Stockholders' Equity, Ending Balance at Mar. 31, 2019	$ 37	396,953	(75)	(296,221)	100,694
Shares, Outstanding, Ending Balance at Mar. 31, 2019	36,575,983
Stockholders' Equity, Beginning Balance at Dec. 31, 2018	$ 32	315,598	(133)	(269,051)	$ 46,446
Shares, Outstanding, Beginning Balance at Dec. 31, 2018	32,364,895
Exercises of vested stock options (in shares)					88,821
Unrealized gain on available for-sale securities, net of tax					$ 234
Net loss					(16,017)
Stockholders' Equity, Ending Balance at Jun. 30, 2019	$ 37	403,334	101	(285,068)	118,404
Shares, Outstanding, Ending Balance at Jun. 30, 2019	36,677,608
Stockholders' Equity, Beginning Balance at Mar. 31, 2019	$ 37	396,953	(75)	(296,221)	100,694
Shares, Outstanding, Beginning Balance at Mar. 31, 2019	36,575,983
Exercises of vested stock options		714			714
Exercises of vested stock options (in shares)	57,461
Issuance of common stock under ESPP		471			471
Issuance of common stock under ESPP (in shares)	44,164
Stock based compensation expense		5,196			5,196
Unrealized gain on available for-sale securities, net of tax			176		176
Net loss				11,153	11,153
Stockholders' Equity, Ending Balance at Jun. 30, 2019	$ 37	$ 403,334	$ 101	$ (285,068)	$ 118,404
Shares, Outstanding, Ending Balance at Jun. 30, 2019	36,677,608

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Cash flow from operating activities
Net loss	$ (16,017)	$ (45,468)
Adjustments to reconcile net loss to net cash provided by operating activities:
Stock-based compensation expense	8,771	10,436
Depreciation	1,292	972
Amortization of premiums and discounts on marketable securities	(1,844)	(908)
In-kind research and development expenses	616	176
Other non-cash items	(832)	355
Changes in operating assets and liabilities:
Collaboration receivable	(8,242)
Unbilled accounts receivable	(1,821)
Prepaid expenses and other current assets	2,966	(1,384)
Operating lease, right-of-use asset	1,382
Other non-current assets	(674)	(180)
Accounts payable	1,192	538
Accrued expenses	1,977	(3,911)
Operating lease liabilities	(1,226)
Deferred revenue	106,065	65,482
Net cash provided by operating activities	93,605	26,108
Cash flow from investing activities
Purchases of property and equipment	(3,168)	(2,933)
Proceeds from sale of equipment	171
Purchases of marketable securities	(314,352)	(205,037)
Proceeds from maturities of marketable securities	177,800	207,000
Net cash used in investing activities	(139,549)	(970)
Cash flow from financing activities
Proceeds from the exercise of stock options	998	2,528
Proceeds from the issuance of common stock in connection with the Neurocrine Collaboration Agreement, net	77,617
Proceeds from the purchase of common stock under ESPP	355	418
Net cash provided by financing activities	78,970	2,946
Net increase in cash, cash equivalents, and restricted cash	33,026	28,084
Cash, cash equivalents, and restricted cash beginning of period	47,594	32,265
Cash, cash equivalents, and restricted cash end of period	80,620	60,349
Supplemental disclosure of cash and non-cash activities
Capital expenditures incurred but not yet paid	$ 17
ASU 2014-09
Supplemental disclosure of cash and non-cash activities
Impact of adopting new accounting standards		$ 20,050

Summary of significant accounting policies and basis of presentation

6 Months Ended

Jun. 30, 2019

Summary of significant accounting policies and basis of presentation

Summary of significant accounting policies and basis of presentation

2. Summary of significant accounting policies and basis of presentation

Basis of Presentation

The accompanying unaudited condensed consolidated financial statements of the Company have been prepared in accordance with accounting principles generally accepted in the United States (“GAAP”) for interim financial reporting and as required by Regulation S-X, Rule 10-01. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. For further information, refer to the consolidated financial statements and footnotes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018 as filed with the Securities and Exchange Commission (“SEC”) on February 26, 2019. These interim condensed consolidated financial statements, in the opinion of management, reflect all normal recurring adjustments necessary for a fair presentation of the Company’s financial position and results of operations for the periods presented. Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASU”) of the Financial Accounting Standards Board (“FASB”). See “Recently Adopted Accounting Pronouncements” below for discussion of the Company’s adoption of new guidance effective January 1, 2019. All amounts and disclosures set forth in this Quarterly Report on Form 10-Q reflect adoption of these changes.

Principles of Consolidation

The unaudited interim consolidated financial statements include the accounts of the Company and its wholly owned subsidiary as disclosed in Note 2, Summary of Significant Accounting Policies, within the “Notes to Consolidated Financial Statements” accompanying the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2018. Intercompany accounts and transactions have been eliminated.

Use of Estimates

The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. On an ongoing basis, the Company’s management evaluates its estimates, which include, but are not limited to, estimates related to revenue recognition, accrued expenses, stock-based compensation expense, and income taxes. The Company bases its estimates on historical experience and other market specific or other relevant assumptions that it believes to be reasonable under the circumstances. Actual results may differ from those estimates or assumptions. Certain reclassifications have been made to prior periods to conform to current period presentation.

Leases

Effective January 1, 2019, the Company accounted for its operating leases in accordance with ASC Topic 842 Leases (“ASC 842”). ASC 842 provides guidance on accounting for lease arrangements by both lessors and lessees and requires lessees to recognize a lease liability and a right-of-use asset for most leases. The Company determines if an arrangement is a lease at inception. The Company’s operating leases are included in operating lease right-of-use (“ROU”) assets, other current liabilities, and other non-current liabilities on the condensed consolidated balance sheets.

ROU assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating lease ROU assets and liabilities are recognized at adoption date based on the present value of lease payments over the lease term. As the Company’s leases do not provide an implicit rate, an incremental borrowing rate was used based on the information available at the lease commencement date in determining the present value of lease payments. On future lease obligations, the implicit rate will be set when readily determinable. The operating lease ROU assets also include the effect of any lease payments made and exclude lease incentives. The Company’s lease terms may include options to

extend or terminate the lease even when it is not reasonably certain that the option will be exercised. Lease expense for lease payments is recognized on a straight-line basis over the lease term. The Company has lease agreements with lease and non-lease components, which are accounted for separately. Non-lease components generally refer to common area maintenance charges related to the premises.

Revenue Recognition

The Company enters into collaboration agreements which are within the scope of ASC 606, Revenue from Contracts with Customers (“ASC 606”), under which the Company licenses rights to certain of the Company’s product candidates and performs research and development services. The terms of these arrangements typically include payment of one or more of the following: non-refundable, upfront fees; reimbursement of research and development costs; development, regulatory, and commercial milestone payments; and royalties on net sales of licensed products.

Under ASC 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine the appropriate amount of revenue to be recognized for arrangements determined to be within the scope of ASC 606, the Company performs the following five steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect consideration it is entitled to in exchange for the goods or services it transfers to the customer.

The promised goods or services in each arrangement typically consist of license rights to the Company’s intellectual property and research and development services. The Company provides options to additional items in the contracts, which are accounted for as separate contracts when the customer elects to exercise such options, unless the option provides a material right to the customer. The Company evaluates the customer options for material rights, or options to acquire additional goods or services for free or at a discount. If the customer options are determined to represent a material right, the material right is recognized as a separate performance obligation at the outset of the arrangement. Performance obligations are promised goods or services in a contract to transfer a distinct good or service to the customer and are considered distinct when (i) the customer can benefit from the good or service on its own or together with other readily available resources and (ii) the promised good or service is separately identifiable from other promises in the contract. In assessing whether promised goods or services are distinct, the Company considers factors such as the stage of development of the underlying intellectual property, the capabilities of the customer to develop the intellectual property on its own or whether the required expertise is readily available and whether the goods or services are integral or dependent to other goods or services in the contract.

The Company estimates the transaction price based on the amount expected to be received for transferring the promised goods or services in the contract. The consideration may include fixed consideration or variable consideration. At the inception of each arrangement that includes variable consideration, the Company evaluates the amount of potential payments and the likelihood that the payments will be received. The Company utilizes either the most likely amount method or expected amount method to estimate the amount expected to be received based on which method best predicts the amount expected to be received. The amount of variable consideration which is included in the transaction price may be constrained, and is included in the transaction price only to the extent that it is probable that a significant reversal in the amount of the cumulative revenue recognized will not occur in a future period.

The Company’s contracts often include development and regulatory milestone payments which are assessed under the most likely amount method and constrained if it is probable that a significant revenue reversal would occur. Milestone payments that are not within the Company’s control or the licensee’s control, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. At the end of each reporting period, the Company re-evaluates the probability of achievement of such development milestones and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect collaboration revenues in the period of adjustment. To date, the Company has not

recognized any consideration related to the achievement of development, regulatory, or commercial milestones resulting from any of the Company’s collaboration arrangements.

For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any consideration related to sales-based royalty revenue resulting from any of the Company’s collaboration arrangements.

The Company allocates the transaction price based on the estimated stand-alone selling price of each of the performance obligations. The Company must develop assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract. The Company utilizes key assumptions to determine the stand-alone selling price for service obligations, which may include other comparable transactions, pricing considered in negotiating the transaction and the estimated costs. Additionally, in determining the standalone selling price for material rights, the Company utilizes comparable transactions, clinical trial success probabilities, and estimates of option exercise likelihood. Variable consideration is allocated specifically to one or more performance obligations in a contract when the terms of the variable consideration relate to the satisfaction of the performance obligation and the resulting amounts allocated are consistent with the amounts the Company would expect to receive for the satisfaction of each performance obligation.

The consideration allocated to each performance obligation is recognized as revenue when control is transferred for the related goods or services. For performance obligations which consist of licenses and other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition.

Upfront payments and fees are recorded as deferred revenue upon receipt or when due until the Company performs its obligations under these arrangements. Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional.

Stock-based Compensation Expense

The Company accounts for its stock-based compensation awards in accordance with ASC Topic 718 Compensation—Stock Compensation (“ASC 718”). ASC 718 requires all stock-based payments to employees, nonemployees, and directors, including grants of restricted stock units and stock options, to be recognized as expense in the statements of operations based on their grant date fair values. The Company estimates the fair value of options granted using the Black-Scholes option pricing model. The Company uses the fair value of its common stock on the grant date to determine the fair value of restricted stock units.

The Black-Scholes option pricing model requires inputs based on certain subjective assumptions, including (a) the expected stock price volatility, (b) the calculation of expected term of the award, (c) the risk-free interest rate and (d) expected dividends. Due to a lack of company-specific historical and implied volatility data, the Company bases the estimate of expected volatility on the historical volatility of a group of similar companies that are publicly traded, blended with the most recent period of historic volatility of its common stock. The historical volatility is calculated based on a period of time commensurate with the expected term assumption. The computation of expected volatility is based on the historical volatility of a representative group of companies with similar characteristics to the Company, including stage of product development and life science industry focus. The Company uses the simplified method as prescribed by the SEC Staff Accounting Bulletin No. 107, Share-Based Payment, to calculate the expected term for stock options granted to employees as it does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term. For stock options granted to non-employees, the Company utilizes the contractual term of the arrangement as the basis for the expected term assumption. The risk-free interest rate is based on a treasury instrument whose term is consistent with the expected term of the stock options. The expected dividend yield is assumed to be zero as the Company has never paid dividends and has no current plans to pay any dividends on its common stock.

The Company expenses the fair value of its stock-based compensation awards on a straight-line basis over the associated service period, which is generally the period in which the related services are received. The Company records the expense for stock-based compensation awards subject to performance conditions over the remaining service period when management determines that achievement of the performance condition is probable. Management evaluates if the achievement of a performance condition is probable based on the expected satisfaction of the performance conditions as of the reporting date.

Net Income (Loss) per Share

Basic net income (loss) per share is computed by dividing net income (loss) by the weighted-average number of common shares and restricted stock unit awards outstanding during the period. Diluted net income (loss) per share is computed using the weighted-average number of common shares and restricted stock unit awards outstanding during the period and, if dilutive, the weighted-average number of potential shares of common stock and restricted stock unit awards.

Recently Adopted Accounting Pronouncements

In February 2016, the FASB issued ASU No. 2016-02, a comprehensive new lease accounting standard, which provides revised guidance on accounting for lease arrangements by both lessors and lessees and requires lessees to recognize a lease liability and a right-of-use asset for most leases. In July 2018, the FASB issued ASU No. 2018-11, Leases-Targeted Improvements (“ASC 842”), which provides an additional transition method that allowed entities to initially apply the new lease requirements at the adoption date, not the earliest period presented, and recognize a cumulative effect adjustment to the opening balance of retained earnings in the period of adoption. The Company elected this transition method at the adoption date of January 1, 2019. The Company elected a package of practical expedients, under which an entity need not reassess whether any expired or existing contracts are or contain leases, the lease classification for any expired or existing leases, or initial direct costs for any existing leases. The impact of adopting ASC 842 was represented as a capitalization of a right-of-use asset of approximately $31.0 million with a corresponding lease liability of approximately $36.7 million to be recognized over the remaining life of the Company’s leases.

In June 2018, the FASB issued ASU No. 2018-07, Compensation-Stock Compensation: Improvements to Nonemployee Share-Based Payment Accounting (“ASU 2018-07”). The new standard largely aligns the accounting for share-based payment awards issued to employees and nonemployees by expanding the scope of ASC 718 to apply to nonemployee share-based transactions, as long as the transaction is not effectively a form of financing. The adoption of ASU 2018-07 on January 1, 2019 did not have a material impact on the Company's consolidated financial statements.

Recent Accounting Pronouncements

In August 2018, the FASB issued ASU No. 2018-13, Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement (“ASU 2018-13”). This standard eliminates, adds and modifies certain disclosure requirements for fair value measurements as part of its disclosure framework project. ASU 2018-13 is effective for annual reporting periods beginning after December 15, 2019 and interim periods within those annual periods and early adoption is permitted. The Company is currently evaluating the potential impact that this guidance may have on its consolidated financial statements.

In June 2016, the FASB issued ASU No. 2016-13, Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”). ASU 2016-13 will change how companies account for credit losses for most financial assets and certain other instruments. For trade receivables, loans and held-to-maturity debt securities, companies will be required to recognize an allowance for credit losses rather than reducing the carrying value of the asset. ASU 2016-13 is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted. The Company is currently evaluating the potential impact that this guidance may have on its consolidated financial statements.

Fair value measurements

6 Months Ended

Jun. 30, 2019

Fair value measurements

Fair value measurements

3. Fair value measurements

Assets and liabilities measured at fair value on a recurring basis as of June 30, 2019 and December 31, 2018 are as follows:


			Quoted Prices		Significant
			in Active		Other		Significant
			Markets for		Observable		Unobservable
			Identical Assets		Inputs		Inputs
Assets	Total		(Level 1)		(Level 2)		(Level 3)
June 30, 2019	(in thousands)
Money market funds included in cash and cash equivalents	$	79,108	$	79,108	$	—	$	—
Marketable securities:
U.S. Treasury notes		247,577		247,577		—		—
Equity securities		1,280		1,280		—		—
Total marketable securities	$	248,857	$	248,857	$	—	$	—
Warrants to purchase equity securities		414		—		414		—
Total	$	328,379	$	327,965	$	414	$	—
December 31, 2018
Money market funds included in cash and cash equivalents	$	46,173	$	46,173	$	—	$	—
Marketable securities:
U.S. Treasury notes		108,947		108,947		—		—
Equity securities		628		628		—		—
Total marketable securities	$	109,575	$	109,575	$	—	$	—
Warrants to purchase equity securities		234		—		234		—
Total	$	155,982	$	155,748	$	234	$	—

The Company measures the fair value of money market funds, U.S. Treasury notes and equity securities based on quoted prices in active markets for identical securities. The Level 2 equity securities include warrants used to purchase equity securities that are valued using the Black-Scholes model. The Black-Scholes option pricing model requires inputs based on certain subjective assumptions, including (a) the expected stock price volatility, (b) the calculation of expected term of the awards, (c) the risk-free interest rate, and (d) expected dividends. The assumptions utilized to value the warrants to purchase equity securities as of June 30, 2019 and December 31, 2018 are as follows:


	As of June 30,		As of December 31,
	2019		2018
Risk-free interest rate	1.7	%	2.5	%
Expected dividend yield	—	%	—	%
Expected term (in years)	2.2		2.7
Expected volatility	88.8	%	112.7	%

The expected volatility is based on the historic volatility for the equity securities underlying the warrants and is calculated based on a period of time commensurate with the expected term assumption. The expected term is based on the remaining contractual life of the warrants on each measurement date. The risk-free interest rate is based on a treasury instrument whose term is consistent with the expected term of the warrants. The expected dividend yield is assumed to be zero as the entity that issued the warrants has never paid and has not indicated any intention to pay dividends.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Cash, cash equivalents, and available-for-sale marketable securities

6 Months Ended

Jun. 30, 2019

Cash, cash equivalents, and available for sale marketable securities

Cash, cash equivalents, and available for sale marketable securities

4. Cash, cash equivalents, and available-for-sale marketable securities

Cash equivalents include all highly liquid investments maturing within 90 days from the date of purchase. Marketable securities consist of securities with original maturities greater than 90 days when purchased. The Company classifies these investments as available-for-sale and records them at fair value in the accompanying condensed

consolidated balance sheets. Unrealized gains or losses are included in accumulated other comprehensive income (loss). Premiums or discounts from par value are amortized to investment income over the life of the underlying investment.

The Company classifies marketable debt securities with a remaining maturity when purchased of greater than three months as available-for-sale. Marketable debt securities with a remaining maturity date greater than one year and marketable equity securities are classified as non-current where the Company has the intent and ability to hold these securities for at least the next 12 months. Available-for-sale debt securities are maintained by an investment manager and consist of U.S. Treasury notes. In 2016, the Company invested in a supplier and received common stock and warrants to purchase common stock in that entity. The common stock is included in non-current marketable securities and the warrants are included in non-current assets.

All available-for-sale securities are carried at fair value with the unrealized gains and losses included in other comprehensive income (loss) as a component of stockholders’ equity until realized. Any premium or discount arising at purchase is amortized and/or accreted to interest income and/or expense. Realized gains and losses are determined using the specific identification method and are included in other income (expense). If any adjustment to fair value reflects a decline in value of the investment, the Company considers all available evidence to evaluate the extent to which the decline is “other-than-temporary” and, if so, recognizes the unrealized loss through a charge to the Company’s condensed consolidated statement of operations and comprehensive loss. No other-than-temporary losses have been recognized.

Cash, cash equivalents, and marketable securities included the following at June 30, 2019 and December 31, 2018:


	Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses		Value
	(in thousands)
As of June 30, 2019
Money market funds included in cash and cash equivalents	$	79,108	$	—	$	—	$	79,108
Marketable securities:
U.S. Treasury notes		247,348		230		1		247,577
Equity securities		1,220		60		—		1,280
Total marketable securities	$	248,568	$	290	$	1	$	248,857
Total money market funds and marketable securities	$	327,676	$	290	$	1	$	327,965
As of December 31, 2018
Money market funds included in cash and cash equivalents	$	46,173	$	—	$	—	$	46,173
Marketable securities:
U.S. Treasury notes		108,951		1		5		108,947
Equity securities		1,220		—		592		628
Total marketable securities	$	110,171	$	1	$	597	$	109,575
Total money market funds and marketable securities	$	156,344	$	1	$	597	$	155,748

All of the Company’s marketable debt securities at June 30, 2019, have a contractual maturity of one year or less.

The following table provides a reconciliation of cash, cash equivalents, and restricted cash within the condensed consolidated balance sheets that sum to the total of the same such amounts shown in the condensed consolidated statement of cash flows:


	As of June 30,		As of December 31,
	2019		2018
	(in thousands)
Cash and cash equivalents	$	79,885	$	46,859
Restricted cash included in deposits and other non-current assets		735		735
Total cash, cash equivalents, and restricted cash	$	80,620	$	47,594

Commitments and contingencies

6 Months Ended

Jun. 30, 2019

Commitments and contingencies

Commitments and contingencies

8. Commitments and contingencies

Significant Agreements

Sanofi Genzyme Collaboration Agreement

Summary of Agreement

In February 2015, the Company entered into a collaboration agreement with Sanofi Genzyme (the “Sanofi Genzyme Collaboration Agreement”), which included a non-refundable upfront payment of $65.0 million. In addition, contemporaneously with entering into the Sanofi Genzyme Collaboration Agreement, Sanofi Genzyme entered into a Series B Stock Purchase Agreement, under which Sanofi Genzyme purchased 10,000,000 shares of Series B Preferred Stock for $30.0 million. The fair value of the Series B Preferred Stock at the time of issuance was approximately $25.0 million. The $5.0 million premium over the fair value is accounted for as additional consideration under the Sanofi Genzyme Collaboration Agreement.

Under the Sanofi Genzyme Collaboration Agreement, the Company granted Sanofi Genzyme an exclusive option to license, develop and commercialize (i) ex-U.S. rights to the following programs, which are referred to as “Split Territory Programs”; VY-AADC (“Parkinson’s Program”), VY-FXN01 (“Friedreich’s ataxia Program”), a future program to be designated by Sanofi Genzyme (“Future Program”), and VY-HTT01 (“Huntington’s Program”) with an incremental option to co-commercialize VY-HTT01 in the United States and (ii) worldwide rights to VY-SMN101 (“Spinal Muscular Atrophy Program”). Sanofi Genzyme’s option for the Split Territory Programs and the Spinal Muscular Atrophy Program is triggered following the completion of the first proof of principle human clinical study (“POP Study”), on a program-by-program basis.

Prior to any option exercise by Sanofi Genzyme, the Company would collaborate with Sanofi Genzyme in the development of products under each Split Territory Program and/or the Spinal Muscular Atrophy Program pursuant to a written development plan and under the guidance of an Alliance Joint Steering Committee (“AJSC”), comprised of an equal number of employees from the Company and Sanofi Genzyme.

Under the Sanofi Genzyme Collaboration Agreement, the Company was required to use commercially reasonable efforts to develop products under each Split Territory Program and the Spinal Muscular Atrophy Program through the completion of the applicable POP Study. During the development of these joint programs, the activities would be guided by a Development Advisory Committee (“DAC”). The DAC could elect to utilize certain Sanofi Genzyme technology relating to the Parkinson’s Program, the Huntington’s Program, or generally with the manufacture of Split Territory Program products.

The Company was solely responsible for all costs incurred in connection with the development of the Split Territory Programs and the Spinal Muscular Atrophy Program products prior to the exercise of an option by Sanofi Genzyme with the exception of the following: (i) at the Company’s request and upon mutual agreement, Sanofi Genzyme would provide “in-kind” services valued at up to $5.0 million and (ii) Sanofi Genzyme would be responsible for the costs and expenses of activities under the Huntington’s Program development plan to the extent such activities were covered by financial support Sanofi Genzyme was entitled to receive from a patient advocacy group.

With the exception of the Parkinson’s Program, Sanofi Genzyme would be required to pay an option exercise payment of $20.0 million or $30.0 million for each Split Territory Program and Spinal Muscular Atrophy Program.

Upon Sanofi Genzyme’s exercise of its option to license a given product in a Split Territory Program (“Split Territory Licensed Product”), the Company would have sole responsibility for the development of such Split Territory Licensed Product in the United States and Sanofi Genzyme would have sole responsibility for development of such Split Territory Licensed Product in the rest of the world. The Company and Sanofi Genzyme would have shared responsibility for execution of ongoing development of such Split Territory Licensed Product that is not specific to either territory, including costs associated therewith. The Company would be responsible for all commercialization activities relating to

Split Territory Licensed Products in the United States, including all of the associated costs. Sanofi Genzyme would be responsible for all commercialization activities relating to the Split Territory Licensed Products in the rest of the world, including all of the associated costs. If Sanofi Genzyme exercised its co-commercialization rights, Sanofi Genzyme would be the lead party responsible for all commercialization activities related to the Huntington’s Program product (the “Huntington’s Licensed Product”) in the United States.

Upon exercise of its option to license a product in the Spinal Muscular Atrophy Program (the “Spinal Muscular Atrophy Licensed Product”), Sanofi Genzyme would have the sole right to develop the Spinal Muscular Atrophy Licensed Product worldwide. Sanofi Genzyme would be responsible for all of the development costs that occur after the option exercise date for the Spinal Muscular Atrophy Program. Sanofi Genzyme would also be responsible for worldwide commercialization activities relating to the Spinal Muscular Atrophy Licensed Product.

In October 2017, Sanofi Genzyme decided not to exercise its option for the Parkinson’s Program (the “PD Opt-Out”). Sanofi Genzyme was required to pay the Company for specified regulatory and commercial milestones, if achieved, up to $540.0 million across all remaining programs. The Company was no longer entitled to receive a total of $105.0 million related to regulatory and commercial milestone payments for the Parkinson’s Program as a result of the PD Opt-Out. The regulatory approval milestones were payable upon either regulatory approval in the United States or regulatory and reimbursement approval in the European Union and ranged from $40.0 million to $50.0 million per milestone, with an aggregate total of $220.0 million, after accounting for the PD Opt-Out. The remaining commercial milestones were payable upon achievement of specified annual net sales in each program and range from $50.0 million to $100.0 million per milestone, with an aggregate total of $320.0 million, after accounting for the PD Opt-Out.

In addition, to the extent any Split Territory Licensed Products or the Spinal Muscular Atrophy Licensed Product were commercialized, the Company would be entitled to tiered royalty payments ranging from the mid-single digits to mid-teens based on a percentage of net sales by Sanofi Genzyme. Sanofi Genzyme would be entitled to receive tiered royalty payments related to sales of a Split Territory Licensed Product ranging from the low-single digits to mid-single digits based on a percentage of net sales by the Company depending on whether the Company uses Sanofi Genzyme technology in the Split Territory Licensed Product. If Sanofi Genzyme elected to co-commercialize the Huntington’s Licensed Product in the United States, the Company and Sanofi Genzyme would share in any profits or losses from Huntington’s Licensed Product sales.

The Sanofi Genzyme Collaboration Agreement was to continue in effect until the later of (i) the expiration of the last to expire of the option rights and (ii) the expiration of all payment obligations unless sooner terminated by the Company or Sanofi Genzyme. The Company and Sanofi Genzyme had customary termination rights, including the right to terminate for an uncured material breach of the agreement committed by the other party, and Sanofi Genzyme had the right to terminate for convenience.

Termination of Agreement

On June 14, 2019, the Company and Sanofi Genzyme executed a termination agreement to terminate the Sanofi Genzyme Collaboration Agreement (the “Sanofi Genzyme Termination Agreement”). Under the terms of the Sanofi Genzyme Termination Agreement, Sanofi Genzyme relinquished its rights to the exclusive license options to the Huntington’s Program, Friedreich’s ataxia Program and the unnamed Future Program. The Company has been relieved of its obligations to perform the research and development services under those programs through completion of the respective POP Studies. As a result, the Company gained worldwide rights to the Huntington's Program and ex-U.S. rights to the Friedreich's ataxia Program. The ex-U.S. rights to the Friedreich’s ataxia Program have been, in turn, transferred from the Company to Neurocrine Biosciences pursuant to the Neurocrine Collaboration Agreement. Additionally, the Company and Sanofi Genzyme entered into an Amended and Restated Option and License Agreement related to AAV capsids (the “Amended Capsid Agreement”). Under the Amended Capsid Agreement, Sanofi Genzyme has obtained exclusive option rights to exclusively license one or more select novel AAV capsids owned or controlled by the Company for exclusive use for up to two non-central nervous system (“non-CNS”) indications.

Sanofi Genzyme has granted the Company exclusive, irrevocable, perpetual, royalty-free, fully-paid sublicensable (through multiple tiers), non-transferable, worldwide licenses in Sanofi Genzyme’s interests in the

collaboration technology generated under or used in the Huntington’s Program and the Friedreich’s ataxia Program with respect to those programs pursuant to the Sanofi Genzyme Collaboration Agreement. In addition, Sanofi Genzyme has granted the Company non-exclusive, irrevocable, perpetual, royalty-free, fully-paid, sublicensable (through multiple tiers), non-transferable, worldwide licenses to the Sanofi Genzyme technology that was contributed to the Sanofi Genzyme Collaboration Agreement and was used in the development or manufacture of product candidates prior to the termination date.

Under the Sanofi Genzyme Termination Agreement, the Company paid Sanofi Genzyme $10.0 million up-front and has agreed to pay Sanofi Genzyme a $10.0 million milestone within fifteen days of the filing of an investigational new drug (“IND”) application for a product candidate incorporating certain intellectual property rights developed under or substantially related to the Huntington’s Program (a “Post-Termination HD Product”). The Company has agreed to pay Sanofi Genzyme (i) 50% of any income received from sublicensing arrangements related to Post-Termination HD Products in excess of specified thresholds and entered into prior to (x) the filing of an IND application for a Post-Termination HD Product or (y) the dosing of the first patient in a clinical trial for a Post-Termination HD Product in the United States or certain European countries, respectively and (ii) a low-double digit percentage of any income received from sublicensing arrangements outside the United States related to products incorporating intellectual property rights developed under, or substantially related to, the Friedreich’s ataxia Program (the “Post-Termination FA Products”) that are in excess of a specified threshold and entered into prior to the dosing of the first patient in a clinical trial for a Post-Termination FA Product in the United States or certain European countries, in each case, subject to certain limitations. The Company has also agreed to pay low-single digit royalties on net sales of Post-Termination HD Products. Under the Sanofi Genzyme Collaboration Agreement, the Company had rights to certain in-kind services. As of the termination date the Company waived its right to approximately $0.4 million in unused in-kind services, and the Company no longer has the right to receive any option payments, regulatory or commercial milestone payments or royalties from Sanofi Genzyme under the Sanofi Genzyme Collaboration Agreement.

The Company has granted Sanofi Genzyme an exclusive royalty-free, fully-paid, sublicensable (through multiple tiers), non-transferable, worldwide license under the Company’s interest in the collaboration technology generated under or used in the Spinal Muscular Atrophy Program pursuant to the Sanofi Genzyme Collaboration Agreement to manufacture, develop, and commercialize any Spinal Muscular Atrophy product. Under the Amended Capsid Agreement, the Company has granted Sanofi Genzyme an exclusive option to evaluate up to four capsids for no consideration. During the capsid evaluation period, the Company has granted Sanofi Genzyme a non-exclusive license to the capsid intellectual property to conduct evaluation studies. In addition, Sanofi Genzyme is able to evaluate up to two additional capsids for a low six-figure payment per additional capsid. The Company is not obligated to perform any additional research on the capsids. Sanofi Genzyme shall have the right to obtain an exclusive license for up to two capsids, each in a specified non-CNS indication. At its discretion, Sanofi Genzyme may exercise both its options for the same capsid for different specified non-CNS indications. Upon its exercise of each option, Sanofi Genzyme has agreed to pay the Company a $1.0 million option exercise fee. Under the Amended Capsid Agreement, the Company is also entitled to receive potential development and regulatory milestone payments upon the achievement of certain milestone events for products containing licensed capsids (“Licensed Products”) of up to an aggregate of $15.0 million per Licensed Product. In addition, for each specified indication, Sanofi Genzyme has agreed to pay to the Company a one-time sales milestone payment of $20.0 million, if aggregate worldwide net sales for all Licensed Products for such specified indication surpass a specified amount, and low-to-mid single-digit tiered royalty payments on worldwide net sales of Licensed Products, on a Licensed Product-by-Licensed Product basis.

Accounting Analysis

At inception, the Sanofi Genzyme Collaboration Agreement included the following performance obligations: (i) research and development services for each of the Split Territory Programs and the Spinal Muscular Atrophy Program, (ii) participation in the AJSC, (iii) participation in the DAC and (iv) a material right associated with an option to obtain a development and commercial license in the Parkinson’s Program (“PD Material Right”). The Company determined that the option to obtain a development and commercial license in the Parkinson’s Program was a material right under ASC 606 primarily because there were no additional option exercise payments payable by Sanofi Genzyme at the time of option exercise. Therefore, the PD Material Right was considered a performance obligation at the inception of the arrangement. The options in the other Split Territory Programs and the Spinal Muscular Atrophy Program do not provide

a material right to the customer that it would receive without entering into the contract principally because the option fees are at least equal to the standalone selling price for the underlying goods. Therefore, the other Split Territory Programs and the Spinal Muscular Atrophy Program options are not performance obligations at inception.

The Company has identified $74.6 million of total transaction price consisting of the $65.0 million upfront fee, the $5.0 million premium paid in excess of fair value of the Series B Preferred Stock and $4.6 million of Sanofi Genzyme “in-kind” funding, which represents the transaction price at adoption. Additional consideration to be paid to the Company upon the exercise of the license options by Sanofi Genzyme or upon reaching certain milestones are excluded from the transaction price as they relate to option fees and milestones that can only be achieved subsequent to the option exercise or are outside of the initial contract term.

The Company has allocated the transaction price to the separate performance obligations based on their relative standalone selling price. For all performance obligations, the Company determined the standalone selling price at contract inception based on each obligation’s estimated standalone selling price (“ESP”). The Company determined the ESP for the service related deliverable for the research and development activities based on internal estimates of the costs to perform the services, including expected internal expenses and expenses with third parties for services and supplies, marked up to include a reasonable profit margin and adjusted for the scope of the potential license. Significant inputs used to determine the total expense of the research and development activities include, the length of time required and the number and costs of various studies that will be performed to complete the applicable POP Study. The ESP for the AJSC and DAC have been estimated based on the costs incurred to participate in the committees, marked up to include a reasonable profit margin. The ESP for the PD Material Right was determined based on the estimated value of the license adjusted for the estimated probability that the option would be exercised by Sanofi Genzyme.

Based on the relative standalone selling price allocation, the allocation of the transaction price to the separate performance obligations was as follows:


Performance Obligation	Amount
	(in thousands)
Research and Development Services for:
Huntington’s Program	$	14,228
Parkinson’s Program		6,040
Friedreich’s ataxia Program		14,821
Spinal Muscular Atrophy Program		29,116
Future Program		2,239
Committee Obligations:
AJSC		133
DAC		207
PD Material Right		7,855
Total	$	74,639

The Company recognizes the amounts associated with research and development services and committee obligations on a proportional performance basis over the period of service using input-based measurements such as costs incurred to date, to estimate proportion performed, and remeasures its progress towards completion at the end of each reporting period. Contingent consideration related to the performance of in-kind services is considered in the transaction price based on the most-likely amount, which is the full amount of the services that the Company can require Sanofi Genzyme to complete. The amount allocated to the PD Material Right was initially deferred and recognized in full prior to the adoption of ASC 606.

During the three and six months ended June 30, 2019, the Company recognized $1.5 million and $2.9 million, respectively, of revenue related to research and development services and committee obligations performed under the Sanofi Genzyme Collaboration prior to the termination of the collaboration on June 14, 2019 (the “Termination Date”). During the three and six months ended June 30, 2018, the Company recognized $0.7 million and $1.2 million, respectively, of revenue to research and development services and committee obligations performed under the Sanofi Genzyme Collaboration.

Costs incurred relating to the programs that Sanofi Genzyme has the option to license under the Sanofi Genzyme Collaboration Agreement consist of internal and external research and development costs, which primarily include: salaries and benefits, lab supplies and preclinical research studies. These costs are included in research and development expenses in the Company’s condensed consolidated statement of operations during the three and six months ended June 30, 2019 and 2018.

The Sanofi Genzyme Termination Agreement modifies both the pricing and scope of the Sanofi Genzyme Collaboration Agreement. As the modification does not add distinct goods or services to the Sanofi Genzyme Collaboration Agreement, the agreement is considered a modification of the original contract.

The Sanofi Genzyme Termination Agreement includes the following performance obligations: (i) worldwide license to collaboration technology and Sanofi Genzyme technology for the development, manufacturing and commercialization of the Huntington’s Program and (ii) worldwide license to collaboration technology and Sanofi Genzyme technology for the development, manufacturing and commercialization for the Friedreich’s ataxia Program. Such performance obligations were satisfied upon the Termination Date as control had transferred upon execution of the Sanofi Genzyme Termination Agreement. Therefore, the remainder of the transaction price under the Sanofi Genzyme Collaboration Agreement, which had not yet been recognized, was recognized as revenue upon the Termination Date.

The Company has recognized $28.7 million of revenue upon the Termination Date. This amount consists of $48.7 million of deferred revenue related to the original agreement as of the Termination Date, offset by (x) $10.0 million related to the fee paid by the Company to Sanofi Genzyme on the Termination Date, and (y) $10.0 million related to the milestone payment which the Company expects to pay to Sanofi Genzyme upon the potential filing of an IND for a product candidate in connection with the Huntington’s Program. Further preclinical studies are underway with VY-HTT01 which, if successful, are expected to support a potential filing of an IND application in 2019. The Company has constrained $10.0 million of the remaining deferred revenue balance at the Termination Date as it expects to pay the milestone payment related to the potential filing of an IND for a product candidate in connection with the Huntington’s Program in 2019. As a result, the Company will maintain a $10.0 million deferred revenue balance associated with the potential milestone payment. This deferral will be reversed upon payment of the milestone to Sanofi Genzyme. If the Company decides not to file an IND for a product candidate in connection with the Huntington’s Program, the Company will recognize that amount as revenue upon determining that the IND filing is no longer likely. The $20.0 million payable by the Company to Sanofi Genzyme is treated as consideration payable to a customer and therefore accounted as a reduction of the transaction price.

In the three and six months ended June 30, 2019, the Company recognized total revenue of $30.2 million and $31.6 million related to services performed and the subsequent termination of the Sanofi Genzyme Collaboration Agreement. At June 30, 2019, $10.0 million remains in deferred revenue in the accompanying condensed consolidated balance sheet.

AbbVie Tau Collaboration Agreement

Summary of Agreement

In February 2018, the Company entered into an exclusive collaboration and option agreement (the “AbbVie Tau Collaboration Agreement”) with AbbVie for the research, development and commercialization of AAV and other virus-based gene therapy products for the treatment of diseases of the central nervous system and other neurodegenerative diseases related to defective or excess aggregation of tau protein in the human brain, including Alzheimer’s disease. Under the AbbVie Tau Collaboration Agreement, the Company and AbbVie have agreed to collaborate on the research and development of specified vectorized antibody compounds comprised of an AAV or other viral capsid and a virus vector genome that encodes one or more antibodies that target and bind to a tau protein. The collaboration is comprised of a research period (the “Research Period”), a development period (the “Development Period”), and an exclusive license option (the “License Option”). The AbbVie Tau Collaboration Agreement included a non-refundable upfront payment of $69.0 million for services during the Research Period.

During the Research Period, each party has agreed to identify up to five antibodies for inclusion in the collaboration. Subject to certain conditions and exceptions, the parties will select up to three antibodies (each, a

“Research Antibody”) as candidates for creation of research compounds (each, a “Research Compound”), with AbbVie having the right to select two of the three Research Antibodies. The Company is required to use diligent efforts to conduct antibody engineering and other research activities to create Research Compounds and to develop product candidates containing or comprised of such Research Compounds (“Product Candidates”). The Company is solely responsible for its costs and expenses during the Research Period. During a specified portion of the Research Period, AbbVie may exercise one or more of its exclusive development options (each, a “Development Option”) to select up to a total of three Research Compounds (the “Selected Research Compounds”) and their corresponding Product Candidates (the “Selected Product Candidates”) to proceed to the Development Period.

Upon AbbVie’s exercise of a Development Option, AbbVie will pay the Company $80.0 million for the first Selected Research Compound and $30.0 million each for up to two additional Selected Research Compounds. During the Development Period, the Company is obligated to use diligent efforts to conduct development activities, including Investigational New Drug application-enabling and Phase 1 clinical trial activities, for the Selected Research Compounds and corresponding Selected Product Candidates. The Company will be solely responsible for the costs and expenses during the Development Period. During a specified portion of the Development Period (the “License Option Period”), AbbVie may exercise its License Option to further develop and commercialize all of the Research Compounds (the “Licensed Compounds”), and corresponding product candidates (the “Licensed Products”). Upon AbbVie’s exercise of its License Option, AbbVie will provide a one-time payment of $75.0 million to the Company, and the Company will grant to AbbVie an exclusive, worldwide license, with the right to sublicense, under certain of the Company’s intellectual property rights to develop and commercialize the Licensed Compounds and the Licensed Products for all human diagnostic, prophylactic and therapeutic uses. In addition, after AbbVie’s exercise of the License Option, the Company has certain obligations to complete any remaining research and development activities that have not been completed for any Research Compounds and Product Candidates.

The Company’s research and development activities will be conducted pursuant to the plans agreed to by the parties and overseen by a joint governance committee (“JGC”) as detailed in the AbbVie Tau Collaboration Agreement. Any material amendment to the research or development plans must be mutually agreed to by the Company and AbbVie, which may be through the JGC.

Under the AbbVie Tau Collaboration Agreement, AbbVie is required to use commercially reasonable efforts to develop and commercialize at least one Licensed Product in each of the United States, Japan, the United Kingdom, Germany, France, Italy, and Spain. After exercise of the License Option, AbbVie is solely responsible for all development and commercialization activities relating to Licensed Compounds and Licensed Products at its sole cost and expense, subject to the agreed-upon research and development plans. The Company may elect to share in AbbVie’s development costs relating to a Licensed Product on an indication-by-indication basis in exchange for a specified increase in royalties (a “Cost-Sharing Option”). If the Company exercises a Cost-Sharing Option, the Company may either reimburse AbbVie for AbbVie’s applicable development costs or, in the case of certain budget overruns, AbbVie may instead deduct applicable development costs, up to a specified cap, from milestone and royalty payments owed by AbbVie to the Company.

Under the AbbVie Tau Collaboration Agreement, the Company is eligible to receive specified development and first-sale milestone payments for each Licensed Compound of up to an aggregate of $550.0 million in the case of an Alzheimer’s disease indication, up to $230.0 million in the case of the first indication other than Alzheimer’s disease and up to $115.0 million for a subsequent non-Alzheimer’s disease indication. Additionally, the Company is eligible to receive tiered, escalating royalties, in a range from a high-single digit to a mid-to-high teen (or, if the Company has exercised its Cost-Sharing Option, low-twenties) percentage of aggregate net sales of Licensed Products on a Licensed Compound by Licensed Compound basis, subject to potential reductions in certain circumstances. For each Licensed Product, AbbVie also has the right to decrease or eliminate its royalty payments on such Licensed Product in exchange for a one-time payment by AbbVie at a fair market value to be negotiated by the parties or determined pursuant to dispute resolution procedures specified in the AbbVie Collaboration Agreement.

Unless earlier terminated, the AbbVie Tau Collaboration Agreement will expire on the earliest to occur of the expiration of (i) the Development Option Period, without AbbVie’s exercise of a Development Option; (ii) the License Option Period, without AbbVie’s exercise of its License Option; and (iii) the last-to-expire royalty term with respect to

all Licensed Products in all countries. The Company and AbbVie have customary termination rights including the right to terminate for an uncured material breach of the agreement committed by the other party, and AbbVie has the right to terminate for convenience.

Accounting Analysis

The Company assessed the promised goods and services under the AbbVie Tau Collaboration Agreement, in accordance with ASC 606, and determined that the AbbVie Tau Collaboration Agreement includes the following performance obligations: (i) research services during the Research Period (through the delivery of the final research report) including the identification of the Research Antibodies, conduct of research activities and provision of information to AbbVie to allow AbbVie to determine whether to exercise up to three development options to be rendered (“Research Services”), and (ii) a material right associated with the Development Option on the first Research Compound and associated Product Candidates (“First Development Option Material Right”). The first Development Option provides AbbVie with (i) additional development services on a selected Research Compound and (ii) the ability to exercise the License Option. The Company has concluded the option provides a material right as the consideration paid by AbbVie upon exercise of the first Development Option is less than the amount that the Company would otherwise expect to receive outside the context of the contract.

The Company has concluded that the First Development Option Material Right is a separate performance obligation under ASC 606 as AbbVie is provided additional services and a License Option for additional consideration that represents a significant discount from amounts that would otherwise be offered outside the context of the contract. The First Development Option Material Right is distinct from the other performance obligations in the arrangement as it is an option in the contract that is not required for AbbVie to obtain the benefit of the other promised goods or services in the arrangement. The First Development Option Material Right does not include the underlying goods or services that are delivered upon exercise of the option, but rather represents the value to the customer of having the right to obtain development services and the right to the License Option at an advantageous price.

The Company received a nonrefundable, upfront payment of $69.0 million as consideration under the AbbVie Collaboration Agreement, which represents the transaction price at inception. Additional consideration to be paid to the Company upon the exercise of the Development and License Options by AbbVie or upon reaching certain milestones are excluded from the transaction price as they relate to option fees and milestones that can only be achieved subsequent to the option exercise or are outside of the initial contact term.

The Company has allocated the transaction price to the separate performance obligations based on their relative standalone selling price. The Company determined the standalone selling price at contract inception based on each obligation’s ESP. The Company determined the ESP for the research services obligation based on internal estimates of the costs to perform the services, including expected internal expenses and expenses with third parties for services and supplies, inclusive of a reasonable profit margin. Significant inputs used to determine the total expense of the research services include the length of time required, the internal hours expected to be incurred on the services and the number and costs of various studies that will be performed to complete the Research Plan. The ESP for the First Development Option Material Right was determined based on the fees AbbVie would pay to exercise the Development and License Options, the estimated costs to perform the development services, inclusive of a reasonable profit margin, the estimated value of the License Option using comparable transactions, and the probability that the Development and License Options would be exercised by AbbVie.

Based on the relative standalone selling price, the allocation of the transaction price to the separate performance obligations was as follows:


Performance Obligation	Amount
	(in thousands)
Research Services	$	34,482
First Development Option Material Right		34,518
Total	$	69,000

The Company recognizes the amounts associated with Research Services on a proportional performance basis over the period of service using input-based measurements of total cost of research incurred to estimate proportion performed and remeasures its progress towards completion at the end of each reporting period. The amount allocated to the First Development Option Material Right is recorded as deferred revenue and will be recognized either over the period in which goods and services underlying the option are transferred or upon expiry of the option.

During the three and six months ended June 30, 2019, the Company recognized $3.2 million and $4.9 million, respectively, of revenue associated with the AbbVie Tau Collaboration related to the Research Services performed during the period. During the three and six months ended June 30, 2018, the Company recognized $1.9 million and $2.3 million, respectively, of revenue associated with the AbbVie Tau Collaboration related to the Research Services performed during the period. As of June 30, 2019, there was $57.1 million of deferred revenue related to the AbbVie Tau Collaboration Agreement, which is classified as either current or non-current in the accompanying condensed consolidated balance sheet based on the period the goods or services are expected to be delivered.

Costs incurred relating to the AbbVie Tau Collaboration Agreement consist of internal and external research and development costs, which primarily include: salaries and benefits, lab supplies, and preclinical research studies. All of these costs are included in research and development expenses in the Company’s condensed consolidated statement of operations during the three and six months ended June 30, 2019.

AbbVie Alpha Synuclein Collaboration Agreement

Summary of Agreement

In February 2019, the Company entered into an exclusive collaboration and option agreement (“the AbbVie Alpha-Synuclein Collaboration Agreement”) with AbbVie, for the research, development and commercialization of AAV and other virus-based gene therapy products directed against pathological species of alpha-synuclein for the potential treatment of Parkinson’s disease and other diseases characterized by the abnormal accumulation of misfolded alpha-synuclein protein (“synucleinopathies”). Under the AbbVie Alpha-Synuclein Collaboration Agreement, the Company and AbbVie have agreed to collaborate on the research and development of specified vectorized antibody compounds comprised of an AAV or other viral capsid and a virus vector genome that encodes one or more antibodies that target and bind to the alpha-synuclein protein. The collaboration is comprised of a research period (the “ASN Research Period”), an optional development period (the “ASN Development Period”), and an exclusive license option (the “ASN License Option”). The AbbVie Alpha-Synuclein Collaboration Agreement included a non-refundable upfront payment of $65.0 million for services during the ASN Research Period.

During the ASN Research Period, the Company is obligated to conduct research activities directed to constructing one or more virus vectors that encode antibodies designated by AbbVie (the “AbbVie Designated Antibodies”) which initially are to be antibodies provided by AbbVie. The Company is obligated to use diligent efforts to conduct research activities to create research compounds (“ASN Research Compounds”) and to develop product candidates containing or comprised of the ASN Research Compounds (“ASN Product Candidates”). The Company is solely responsible for the costs and expenses during the ASN Research Period. During a specified portion of the ASN Research Period, AbbVie may exercise one or more of its exclusive development options to select up to a total of four ASN Research Compounds and their corresponding ASN Product Candidates to proceed to the ASN Development Period.

Upon AbbVie’s exercise of an option to proceed to the ASN Development Period (an “ASN Development Option”), AbbVie will pay the Company $80.0 million for the first ASN Research Compound and $30.0 million each for up to three additional ASN Research Compounds. During the ASN Development Period, the Company is obligated to use diligent efforts to conduct development activities, including IND application-enabling and Phase 1 clinical trial activities, for each selected ASN Research Compound and corresponding selected ASN Product Candidates. The Company is solely responsible for the costs and expenses during the ASN Development Period. During a specified portion of the ASN Development Period, AbbVie may exercise its ASN License Option to further develop and commercialize all of the ASN Research Compounds and corresponding ASN Product Candidates. Upon AbbVie’s

exercise of its ASN License Option, the Company has agreed to grant to AbbVie an exclusive, worldwide license, with the right to sublicense, under certain of the Company’s intellectual property rights to develop and commercialize the licensed compounds and the licensed products for all human diagnostic, prophylactic and therapeutic uses. In addition, after AbbVie’s exercise of the ASN License Option, the Company has certain obligations to complete any remaining research and development activities that have not been completed for any ASN Research Compounds and ASN Product Candidates.

The Company’s research and development activities are to be conducted pursuant to the plans agreed to by the parties and overseen by a joint governance committee (or “ASN JGC”) as detailed in the AbbVie Alpha-Synuclein Collaboration Agreement. Any material amendment to the research or development plans, however, must be mutually agreed to by the parties, which may be through the ASN JGC.

Under the AbbVie Alpha-Synuclein Collaboration Agreement, AbbVie is required to use commercially reasonable efforts to develop and commercialize at least one licensed product in each of the United States, Japan, the United Kingdom, Germany, France, Italy and Spain. After exercise of the ASN License Option, AbbVie is solely responsible for all development and commercialization activities relating to licensed compounds and licensed products at its sole cost and expense, subject to the Company’s obligation to complete any remaining research and development activities set forth in the agreed-upon research and development plans.

Under the terms of the AbbVie Alpha-Synuclein Collaboration Agreement, the Company is eligible to receive (i) specified development and first-sale milestone payments for each licensed compound of up to an aggregate of $450.0 million in the case of a Parkinson’s disease indication and up to $185.0 million in the case of the first indication other than Parkinson’s disease and $92.5 million for a subsequent non-Parkinson’s disease indication; (ii) specified commercial milestone payments based on net sales for all licensed products and all indications up to an aggregate of $500.0 million; and (iii) tiered, escalating royalties, in the mid-single digit percentage range for aggregate net sales of licensed products on a licensed compound by licensed compound basis, subject to potential reductions in certain circumstances.

Unless earlier terminated, the AbbVie Alpha-Synuclein Collaboration Agreement expires on the earliest to occur of the expiration of (i) the ASN Development Period, without AbbVie’s exercise of an ASN Development Option; (ii) the license option period, without AbbVie’s exercise of its ASN License Option; and (iii) the last-to-expire royalty term with respect to all licensed products in all countries. The Company and AbbVie have customary termination rights including the right to terminate for an uncured material breach of the agreement committed by the other party, and AbbVie has the right to terminate for convenience.

Upon termination in certain cases, the vectorized antibody exclusivity and AbbVie designated exclusivity survives until the third anniversary of the termination date. If the parties mutually agree to terminate for infeasibility or AbbVie terminates for the Company’s failure to deliver a final research or development report, neither the Company nor any of its affiliates may directly or indirectly exploit a vectorized antibody compound that targets or binds to the alpha-synuclein protein for 18 months after the termination date.

Accounting Analysis

The Company assessed the promised goods and services under the AbbVie Alpha-Synuclein Collaboration Agreement, in accordance with ASC 606, and determined that the AbbVie Alpha-Synuclein Collaboration Agreement includes the following performance obligations: (i) research services during the ASN Research Period (through the delivery of the final research report) including the conduct of research activities and provision of information to AbbVie to allow AbbVie to determine whether to exercise up to four ASN Development Options (collectively, the “ASN Research Services”), and (ii) a material right associated with the first ASN Development Option on the first ASN Research Compound and associated ASN Product Candidates (“ASN First Development Option Material Right”). The exercise of the first ASN Development Option provides AbbVie with (i) additional development services on a selected ASN Research Compound and (ii) the ability to exercise the ASN License Option. The Company has concluded the option provides a material right as the consideration paid by AbbVie upon exercise of the first ASN Development Option is less than the amount that the Company would otherwise expect to receive outside the context of the contract.

The Company has concluded that the ASN First Development Option Material Right is a separate performance obligation under ASC 606 as AbbVie is provided additional services and an ASN License Option for additional consideration that represents a significant discount from amounts that would otherwise be offered outside the context of the contract. The ASN First Development Option Material Right is distinct from the other performance obligations in the arrangement as it is an option in the contract that is not required for AbbVie to obtain the benefit of the other promised goods or services in the arrangement. The ASN First Development Option Material Right does not include the underlying goods or services that are delivered upon exercise of the option, but rather represents the value to the customer of having the right to obtain development services and the right to the ASN License Option at an advantageous price.

The Company received a nonrefundable, upfront payment of $65.0 million as consideration under the AbbVie Alpha-Synuclein Collaboration Agreement, which represents the transaction price at inception. Additional consideration to be paid to the Company upon the exercise of the ASN Development and ASN License Options by AbbVie or upon reaching certain milestones are excluded from the transaction price as they relate to option fees and milestones that can only be achieved subsequent to the option exercise or are outside of the initial contact term.

The Company has allocated the transaction price to the separate performance obligations based on their relative standalone selling price. The Company determined the standalone selling price at contract inception based on each obligation’s ESP. The Company determined the ESP for the research services obligation based on internal estimates of the costs to perform the services, including expected internal expenses and expenses with third parties for services and supplies, inclusive of a reasonable profit margin. Significant inputs used to determine the total expense of the research services include the length of time required, the internal hours expected to be incurred on the services and the number and costs of various studies that will be performed to complete the agreed upon ASN research plan. The ESP for the ASN First Development Option Material Right was determined based on the fees AbbVie would pay to exercise the ASN Development and ASN License Options, the estimated costs to perform the development services, inclusive of a reasonable profit margin, the estimated value of the ASN License Option using comparable transactions, and the probability that the ASN Development and License Options would be exercised by AbbVie.

Based on the relative standalone selling price, the allocation of the transaction price to the separate performance obligations was as follows:


Performance Obligation	Amount
	(in thousands)
ASN Research Services	$	23,768
ASN First Development Option Material Right		41,232
Total	$	65,000

The Company recognizes the amounts associated with the ASN Research Services on a proportional performance basis over the period of service using input-based measurements of total cost of research incurred to estimate proportion performed and remeasures its progress towards completion at the end of each reporting period. The amount allocated to the ASN First Development Option Material Right is recorded as deferred revenue and will be recognized either over the period in which goods and services underlying the option are transferred or upon expiry of the option.

During the three and six months ended June 30, 2019, the Company recognized $0.2 million and $0.4 million of revenue, respectively, associated with the AbbVie Alpha-Synuclein Collaboration related to the ASN Research Services performed during the period then ended. As of June 30, 2019, there was $64.6 million of deferred revenue related to the AbbVie Alpha-Synuclein Collaboration Agreement, which is classified as either current or non-current in the accompanying condensed consolidated balance sheet based on the period the goods or services are expected to be delivered.

Costs incurred relating to the AbbVie Alpha-Synuclein Collaboration Agreement consist of internal and external research and development costs, which primarily include salaries and benefits, lab supplies, and preclinical

research studies. All of these costs are included in research and development expenses in the Company’s condensed consolidated statement of operations during the three and six months ended June 30, 2019.

Neurocrine Collaboration Agreement

Summary of Agreement

In March 2019, the Company entered into an exclusive collaboration and option agreement with Neurocrine Biosciences (the “Neurocrine Collaboration Agreement”) for the research, development and commercialization of certain of its AAV gene therapy products. Under the Neurocrine Collaboration Agreement, the Company has agreed to collaborate on the conduct of four collaboration programs (the “Neurocrine Programs”) which include: (i) the AADC Program (the “AADC Program”) for the treatment of Parkinson’s disease, (ii) the FA Program (the “FA Program”) for the treatment of Friedreich’s ataxia including the development of the VY-FXN01 product candidate (collectively, the “Existing Programs”); and (iii) two programs to be determined by the Company and Neurocrine at a later date (the “Discovery Programs”).

In June 2019, in conjunction with the termination of the Sanofi Genzyme Collaboration Agreement, the Company gained ex-U.S. rights to the VY-FXN01 Friedreich's ataxia Program. The ex-U.S. rights to VY-FXN01 were subsequently transferred from the Company to Neurocrine Biosciences under the terms of the Neurocrine Collaboration Agreement. To facilitate the transfer of the ex-U.S. rights to VY-FXN01 from the Company to Neurocrine, the Company and Neurocrine Biosciences executed an amendment to the Neurocrine Collaboration Agreement (the “June 2019 Modification”), and Neurocrine Biosciences paid $5.0 million to the Company. There were no other changes in pricing or scope of the obligations required to be performed under the Neurocrine Collaboration Agreement.

Under the terms of the Neurocrine Collaboration Agreement, the Company has agreed to collaborate with Neurocrine on, and to grant, exclusive, royalty-bearing, non-transferable, sublicensable licenses to certain of its intellectual property rights, for all human and veterinary diagnostic, prophylactic, and therapeutic uses, for the research, development, and commercialization of gene therapy products (the “Collaboration Products”) on a worldwide basis under (i) the AADC Program; (ii) the FA Program; and (iii) each Discovery Program.

Pursuant to development plans to be agreed by the parties, which will be overseen by a joint steering committee (“JSC”), the Company has operational responsibility, subject to certain exceptions, for the conduct of each Neurocrine Program prior to the defined Transition Event for each Program, as described below, and is required to use commercially reasonable efforts to develop the corresponding Collaboration Products. Neurocrine has agreed to be responsible for all costs incurred by the Company in conducting these activities for each Neurocrine Program, in accordance with an agreed budget for each Neurocrine Program. If the Company breaches its development responsibilities or in certain circumstances upon a change in control, Neurocrine has the right but not the obligation to assume the activities under such Neurocrine Program.

Upon the occurrence of a specified event for each Neurocrine Program (a “Transition Event”) Neurocrine has agreed to assume responsibility for development, manufacturing and commercialization activities for such Neurocrine Program from the Company and to pay milestones and royalties on future net sales as described further below. The Transition Events are (i) with respect to the AADC Program, the Company’s receipt of topline data for the RESTORE-1 Phase 2 clinical trial for VY-AADC; (ii) with respect to the FA Program, the Company’s receipt of topline data for the initial Phase 1 clinical trial for a Friedreich’s ataxia program product candidate; and (iii) with respect to each Discovery Program, the preparation by the Company and the approval by Neurocrine of an IND application to be filed with the Food and Drug Administration (the “FDA”) by Neurocrine for the first development candidate in such Discovery Program. For each Existing Program, the Company has the option (the “Co-Co Option”) to co-develop and co-commercialize such Neurocrine Program upon the occurrence of a specified event (a “Co-Co Trigger Event”). Should the Company elect to exercise its Co-Co Option, the Company has agreed to enter into a cost- and profit-sharing arrangement with Neurocrine (a “Co-Co Agreement”), whereby it has agreed to jointly develop and commercialize Collaboration Products for such Neurocrine Existing Program (“Co-Co Products”) and share in its costs, profits and losses, and the Company agrees to forfeit certain milestones and royalties on net sales in the United States during the effective period of the applicable Co-Co Agreement. The Co-Co Trigger Events are (i) with respect to the AADC

Program, the Company’s receipt of topline data for the ongoing RESTORE-1 Phase 2 clinical trial for VY-AADC and (ii) with respect to the FA Program, the receipt of topline data for the initial Phase 1 clinical trial for a Friedreich’s ataxia program product candidate.

Subject to exceptions specified in the Neurocrine Collaboration Agreement, profits and losses under the Company’s Co-Co Option are agreed to be allocated (i) 50% to Neurocrine and 50% to the Company for a Collaboration Product from the AADC Program and (ii) 60% to Neurocrine and 40% to the Company for a Collaboration Product from the FA Program; provided, however, that Neurocrine may elect, within a specified period following the acceptance for filing of a BLA from the FDA, to pay a $35.0 million rate-shifting fee to the Company to change the allocation for the AADC Program to 55% to Neurocrine and 45% to the Company. The parties have agreed that each Co-Co Agreement will provide the Company the right to terminate for any reason upon prior written notice to Neurocrine and Neurocrine the right to terminate in certain circumstances upon change of control.

The Company’s research and development activities under the Neurocrine Collaboration Agreement are to be conducted pursuant to plans agreed to by the parties, on a program-by-program basis, and overseen by the JSC, as detailed in the Neurocrine Collaboration Agreement.

The parties have committed to agree on a list of up to eight target genes (or “Targets”) from which Neurocrine has the right to nominate Targets for the two Discovery Programs. Each Target for the Discovery Programs must be approved by a consensus of the JSC or the executive officers.

The Neurocrine Collaboration Agreement provides for an upfront non-refundable payment of $115.0 million, as well as for aggregate development and regulatory milestone payments from Neurocrine to the Company for Collaboration Products under (i) the AADC Program of up to $170.0 million; (ii) the FA Program of up to $195.0 million, and (iii) each of the two Discovery Programs of up to $130.0 million per Discovery Program. The Company may be entitled to receive aggregate commercial milestone payments for each Collaboration Product of up to $275.0 million, subject to an aggregate cap on commercial milestones across all Neurocrine Programs of $1.1 billion. Furthermore, in connection with the Neurocrine Collaboration Agreement, Neurocrine has purchased 4,179,728 shares of the Company’s common stock at a price of $11.9625 per share, for an aggregate purchase price of $50.0 million.

Neurocrine has also agreed to pay the Company royalties, based on future net sales of the Collaboration Products. Such royalty percentages, for net sales in and outside the United States, as applicable, range (i) for the VY-AADC program, from the mid-teens to low thirties and the low-teens to low twenties, respectively; (ii) for the FA Program, from the low-teens to high-teens and high-single digits to mid-teens, respectively; and (iii) for each Discovery Program, from the high-single digits to mid-teens and mid-single digits to low-teens, respectively. On a country-by-country and program-by-program basis, royalty payments would commence on the first commercial sale of a Collaboration Product and terminate on the later of (a) the expiration of the last patent covering the Collaboration Product or its method of use in such country, (b) 10 years from the first commercial sale of the Collaboration Product in such country and (c) the expiration of regulatory exclusivity in such country, or the Royalty Term. Royalty payments may be reduced by up to 50% in specified circumstances, including expiration of patents rights related to a Collaboration Product, approval of biosimilar products in a given country or required payment of licensing fees to third parties related to the development and commercialization of any Collaboration Product. Additionally, the licenses granted to Neurocrine shall automatically convert to fully paid-up, non-royalty bearing, perpetual, irrevocable, exclusive licenses on a country-by-country and product-by-product basis upon the expiration of the Royalty Term applicable to such Collaboration Product in such country.

Under the terms of the Neurocrine Collaboration Agreement and subject to specified exceptions therein, each party owns the entire right, title and interest in and to all intellectual property rights made solely by its employees or agents in the course of the collaboration. The parties jointly own all rights, title and interest in and to all intellectual property rights made or invented jointly by employees or agents of both parties.

During the term of the Neurocrine Collaboration Agreement, neither party nor any of its respective affiliates is permitted to directly or indirectly exploit any AAV-based gene therapy products directed to a Target to which a Collaboration Product is directed, subject to specified exceptions including the parties’ conduct of basic research.

Unless earlier terminated, the Neurocrine Collaboration Agreement expires on the later of (i) the expiration of the last to expire royalty term with respect to a Collaboration Product in all countries in the relevant territory or (ii) the expiration or termination of all Co-Co Agreements. Neurocrine may terminate the Neurocrine Collaboration Agreement in its entirety or on a program-by-program or country-by-country basis by providing at least (x) 180-day advance notice if such notice is provided prior to the first commercial sale of the Collaboration Product to which the termination applies or (y) one-year advance notice if such notice is provided after the first commercial sale of the Collaboration Product to which the termination applies. The Company may terminate the Neurocrine Collaboration Agreement, subject to specified conditions, if Neurocrine challenges the validity or enforceability of certain of the Company’s intellectual property rights. Subject to a cure period, either party may terminate the Neurocrine Collaboration Agreement in the event of a material breach by the other party in whole or in part, subject to specified conditions.

Upon termination in certain cases, Neurocrine has agreed to grant to the Company licenses to certain Neurocrine intellectual property, subject to a negotiation between the parties to establish royalty rates for use of such intellectual property. In the event of a breach by the Company with respect to a Neurocrine Program, if such termination were to occur after a Transition Event, then (i) if a Co-Co Agreement is in effect with respect to such program, Neurocrine can terminate the Co-Co Agreement for such program and the Company would no longer have co-development and co-commercialization rights with respect to the Collaboration Product and (ii) subject to any license agreements, Neurocrine would no longer have any obligations with respect to any Collaboration Products resulting from such program.

Accounting Analysis

At inception, the Neurocrine Collaboration Agreement included the following performance obligations: (i) research and development services for each Existing Program combined with a development and commercialization license for each such program and (ii) research and development services for each Discovery Program combined with a development and commercialization license for each program. The research services and license on a program by program basis are not distinct as Neurocrine cannot benefit from such license on its own or from other resources commonly available in the industry, without the corresponding research services due to the unique and specialized expertise of the Company that is not readily available in the marketplace.

The Company has identified $92.4 million of fixed transaction price consisting of the $115.0 million upfront fee and $5.0 million payment from the June 2019 Modification, offset by a discount of $27.6 million related to the $50.0 million equity investment of 4,179,728 shares when measured at fair value on the date of issuance. The Company is also entitled to reimbursement of costs incurred by the Company prior to the Transition Events associated with each Neurocrine Program. These amounts are determinable based on program plans and budgets, and the Company has a contractual right to the payment of cost incurred under the agreed upon program plans. The Company has utilized the most likely amount approach to estimate the cost reimbursement to be $431.1 million, and has concluded that these amounts do not require a constraint and are included in the transaction price at inception. Additional consideration to be paid to the Company upon reaching certain milestones are excluded from the transaction price at inception due to the uncertainty of achieving the development and regulatory milestones.

The Company has allocated the fixed transaction price to the separate performance obligations based on the relative standalone selling price of each performance obligation or in the case of certain variable consideration to one or more performance obligations. The estimated standalone selling prices for performance obligations, that include a license and research services, were developed using the estimated selling price of the license, using comparable and market date, and an estimate of the overall effort to perform the research services along with a reasonable profit for research services.

The Company has concluded that the variable consideration related to the cost reimbursement of each program will be allocated to each respective program as the cost reimbursement relates specifically to the respective program services being performed under the Neurocrine Collaboration. The reimbursement of research services is considered to be at a market rate and the allocation of the fixed consideration to all of the performance obligations depicts the estimated amounts in which it would expect to receive for these obligations, absent the variable consideration related to

the research reimbursement. The total variable consideration allocated to each program related to the cost reimbursement was as follows:


Performance Obligation	Amount
	(in thousands)
Variable Consideration
AADC Program	$	170,209
FA Program		114,023
Discovery Program 1		73,416
Discovery Program 2		73,416
Total	$	431,064

Based on the relative standalone selling price allocation, the allocation of the transaction price, exclusive of the variable consideration allocated to the individual performance obligations, to the separate performance obligations was as follows:


Performance Obligation	Amount
	(in thousands)
Fixed Consideration
AADC Program	$	80,373
FA Program		6,005
Discovery Program 1		3,002
Discovery Program 2		3,002
Total	$	92,382

The Company recognizes the transaction price associated with each performance obligation on a proportional performance basis over the period of service using input-based measurements such as costs incurred to date, to estimate proportion performed, and remeasures its progress towards completion at the end of each reporting period.

During the three and six months ended June 30, 2019, the Company recognized $12.5 million and $14.4 million of revenue, respectively, associated with its collaboration with Neurocrine related to research and development services performed during the period and the corresponding cost reimbursement receivable. As of June 30, 2019, there was $88.0 million of deferred revenue related to the Neurocrine Collaboration Agreement, which is classified as either current or non-current in the accompanying condensed consolidated balance sheet based on the period the services are expected to be delivered. Additionally, as of June 30, 2019, there was $10.1 million of collaboration and unbilled receivables related to reimbursable costs expected to be received from Neurocrine for research and development services performed.

Costs incurred relating to the Collaboration Programs consist of internal and external research and development costs, which primarily include: salaries and benefits, lab supplies, preclinical research studies, clinical studies, consulting services, and commercial development. These costs are included in research and development expenses in the Company’s condensed consolidated statement of operations during the three and six months ended June 30, 2019.

The Company incurred approximately $0.8 million of costs to obtain the Neurocrine Collaboration Agreement which were payable only upon the close of the deal and therefore considered incremental costs of obtaining a contract with a customer and capitalized. The costs are recorded in prepaid expenses and other non-current assets and are being amortized over the period in which the research services will be provided.

MRI Interventions License and Securities Purchase Agreements

In September 2016, the Company entered into a securities purchase agreement (the “Securities Purchase Agreement”) and a license agreement (the “MRIC License Agreement”) with MRI Interventions, Inc. (“MRIC”). MRIC is the primary supplier of the ClearPoint^® System, which is being used by the Company in ongoing development and clinical trials. Under the Securities Purchase Agreement, the Company paid $2.0 million for shares of MRIC common stock and a warrant to purchase additional shares of MRIC common stock. The Company also entered into the MRIC

License Agreement, which provided for certain rights to MRIC technology and for MRIC to transfer the rights and know-how to manufacture the ClearPoint System to enable the Company to utilize an alternative supplier for the ClearPoint System for use in the Company’s development and clinical trials. During 2017, the Company terminated the MRIC License Agreement and all prior and future commitments and obligations under such agreement became null and void. As of June 30, 2019, the Company continues to hold the common stock and warrants to purchase additional shares of common stock as an available-for-sale security and non-current asset, respectively.

In May 2018, the Company entered into a master services and supply agreement with MRIC (the “MRIC Supply Agreement”) which provides for MRIC to perform certain manufacturing, supply, development and services as requested by the Company, including the supply of the ClearPoint System and cannula devices. In March 2019, in connection with the MRIC Supply Agreement, the Company transferred its premarket notification (510(k)) clearance for its Variable Trajectory Array Guide (“V-TAG”) delivery device to MRIC and MRIC assumed the role of specifications developer and manufacturer for the V-TAG device and related regulatory compliance obligations. Under the terms of the MRIC Supply Agreement, MRIC will manufacture and supply the V-TAG device exclusively to the Company’s clinical sites for use in the RESTORE-1 Phase 2 clinical trial. The Company retained all of its intellectual property rights in the V-TAG device, and has the unrestricted right to require MRIC to transfer the 510(k) clearance back to the Company at the Company’s request.

Other Agreements

During 2018 and 2017, the Company entered into various agreements with contract research organizations and institutions to license intellectual property. In consideration for the rights licensed under such agreements, the Company generally made upfront payments, which were recorded as research and development expense as the acquired technologies were considered in-process research and development. The agreements generally obligate the Company to make additional payments that are contingent upon specific clinical trial and regulatory approval milestones being achieved as well as royalties on future product sales. The agreements to license intellectual property include potential milestone payments that are dependent upon the development of products licensed under the agreements and contingent upon the achievement of clinical trial or regulatory approval milestones. As of June 30, 2019, the Company reached a milestone related to first patient dosing on the RESTORE-1 Phase 2 clinical trial which resulted in a $0.1 million milestone payment to one of its licensors. The Company can generally terminate the license agreements upon 30 to 90 days prior written notice.

During the year ended December 31, 2016, the Company entered into a research and development funding arrangement with a non-profit organization that provides up to $4.0 million in funding to the Company upon the achievement of clinical and development milestones. The agreement provides that the Company repay amounts received under certain circumstances including termination of the agreement, and to pay an amount up to 2.6 times the funding received upon successful development and commercialization of any products developed. During the year ended December 31, 2017, the Company earned a milestone payment of $1.0 million. The Company has evaluated the arrangement and has concluded that it represents a research and development financing arrangement as it is probable that the Company will repay amounts received under the arrangement. As a result, the $1.0 million earned to date is recorded as a non-current liability in the condensed consolidated balance sheet.

Litigation

The Company is not a party to any material legal matters or claims and did not have contingency reserves established for any litigation liabilities as of June 30, 2019 or December 31, 2018.

Stock based compensation

6 Months Ended

Jun. 30, 2019

Stock based compensation

Stock based compensation

10. Stock-based compensation

2014 Stock Option and Grant Plan

In January 2014, the Company adopted the 2014 Stock Option and Grant Plan (the “2014 Plan”), under which it could grant incentive stock options, non-qualified stock options, restricted stock awards, unrestricted stock awards, or restricted stock units to purchase up to 823,529 shares of common stock to employees, officers, directors and consultants of the Company.

In April 2014, the Company amended the 2014 Plan to allow for the issuance of up to 1,411,764 shares of common stock. In August 2014, April 2015, August 2015, and October 2015, the Company further amended the 2014 Plan to allow for the issuance of up to 2,000,000, 2,047,058, 2,669,411, and 2,998,823 shares of common stock, respectively. During 2014 the Company issued only restricted stock awards under the 2014 Plan and during 2015 the Company only granted stock options under the 2014 Plan.

The terms of stock option agreements, including vesting requirements, were determined by the Board of Directors and were subject to the provisions of the 2014 Plan. Restricted stock awards granted by the Company generally vest based on each grantee’s continued service with the Company during a specified period following grant. Stock options granted to employees generally vest over four years, with 25% vesting on the one year anniversary and 75% vesting ratably, on a monthly basis, over the remaining three years. Stock options granted to non-employee consultants generally vest monthly over a period of one to four years.

Founder Awards

In January 2014, the Company issued 1,188,233 shares of restricted stock to its founders at an original issuance price of $0.0425 per share. Of the total restricted shares awarded to the founders, 835,292 shares generally vested over one to four years, based on each founder’s continued service to the Company in varying capacity as a Scientific Advisory Board member, consultant, director, officer or employee, as set forth in each grantee’s individual restricted stock purchase agreement. These shares were fully vested as of June 30, 2019. Stock-based compensation expense associated with these time-based awards was recognized over the vesting period.

The remaining 352,941 of the shares issued begin vesting upon the achievement of certain performance objectives as well as continued service to the Company, as set forth in the agreements. These performance conditions are tied to certain milestone events specific to the Company’s corporate goals, including but not limited to preclinical and clinical development milestones related to the Company’s product candidates. Stock-based compensation expense associated with these performance-based awards is recognized when the achievement of the performance condition is considered probable, using management’s best estimates. During 2016, management determined that the achievement of the performance milestone for one of the three performance-based awards had become probable and began recognizing stock-based compensation accordingly. The Company recorded $0.1 million and $0.3 million in stock-based compensation expense related to this award during the three and six months ended June 30, 2018, respectively. No stock-based compensation expense was recorded in 2019 related to this award as it was fully vested during 2018. No stock-based compensation expense was recorded for the remaining two founders’ awards with performance-based vesting as of June 30, 2019 as the performance-based milestones related to these awards were not probable.

2015 Stock Option Plan

In October 2015, the Company’s board of directors and stockholders approved the 2015 Stock Option and Incentive Plan (the “2015 Stock Option Plan”), which became effective upon the completion of the Company’s initial public offering (the “IPO”). The 2015 Stock Option Plan provides the Company with the flexibility to use various equity-based incentive and other awards as compensation tools to motivate its workforce. These tools include stock options, stock appreciation rights, restricted stock, restricted stock units, unrestricted stock, performance share awards and cash-based awards. The 2015 Stock Option Plan replaced the 2014 Plan. Any options or awards outstanding under the 2014 Plan remained outstanding and effective. The number of shares initially reserved for issuance under the 2015 Stock Option Plan is the sum of (i) 1,311,812 shares of common stock and (ii) the number of shares under the 2014 Plan that are not needed to fulfill the Company’s obligations for awards issued under the 2014 Plan as a result of forfeiture, expiration, cancellation, termination or net issuances of awards thereunder. The number of shares of common stock that

may be issued under the 2015 Stock Option Plan is also subject to increase on the first day of each fiscal year by up to 4% of the Company’s issued and outstanding shares of common stock on the immediately preceding December 31.

Effective January 1, 2016, 2017, 2018, and 2019, an additional 1,069,971, 1,070,635, 1,285,200, and 1,302,830 shares, respectively, were added to the Company’s 2015 Stock Option Plan for future issuance. As of June 30, 2019, there were 2,166,946 shares of common stock available for future award grants under the 2015 Stock Option Plan. During the three and six months ended June 30, 2019, the Company granted a total of 557,580 and 1,310,920 stock options, respectively, to employees and directors under the 2015 Stock Option Plan. During the three and six months ended June 30, 2019, the Company awarded a total of 65,052 and 419,457 restricted stock units, respectively, to employees under the 2015 Stock Option Plan. During the three and six months ended June 30, 2019, there were no new stock options issued to non-employees under the 2015 Stock Option Plan.

2015 Employee Stock Purchase Plan

In October 2015, the Company’s board of directors and stockholders approved the 2015 Employee Stock Purchase Plan (the “2015 ESPP”). The 2015 ESPP became effective upon the closing of the IPO. Under the 2015 ESPP, all full-time employees of the Company are eligible to purchase common stock of the Company twice per year, at the end of each six-month payment period. During each payment period, eligible employees who so elect, may authorize payroll deductions in an amount of 1% to 10% (whole percentages only) of the employee’s base pay for each payroll period. At the end of each payment period, the accumulated deductions are used to purchase shares of common stock from the Company at a discount. A total of 262,362 shares of common stock were initially authorized for issuance under this plan. The number of shares of common stock that may be issued under the 2015 ESPP is also subject to increase on the first day of each fiscal year by up to 1% of the Company’s issued and outstanding shares of common stock on the immediately preceding December 31. Effective January 1, 2016, 2017, 2018, and 2019, 267,492, 267,658, 321,300, and 325,707 shares of common stock, respectively, were added to the 2015 ESPP.

Inducement Awards

In the three and six months ended June 30, 2019, the Company issued to two executives non-statutory stock options to purchase an aggregate of 338,750 shares of the Company’s common stock and restricted stock unit awards for an aggregate of 58,125 units of the Company’s common stock, in each case outside of the Company’s 2015 Stock Option Plan as an inducement material to such executive’s acceptance of an offer of employment with the Company in accordance with Nasdaq Listing Rule 5635(c)(4). The stock options will vest over a four-year period, with 25% of the shares underlying the option award vesting on the first anniversary of the award and the remaining 75% of the shares underlying the award vesting monthly thereafter over the subsequent 36-month period. The restricted stock units will vest over a three-year period, with 33% of the restricted stock units vesting on the first anniversary, 33% of the restricted stock units vesting on the second anniversary, and the remaining restricted stock units vesting on the third anniversary.

Stock-Based Compensation Expense

Total compensation cost recognized for all stock-based compensation awards in the statements of operations and comprehensive income (loss) is as follows:


	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2019		2018		2019		2018
	(in thousands)
Research and development	$	3,256	$	1,332	$	4,671	$	2,530
General and administrative		1,998		6,782		4,100		7,906
Total stock-based compensation expense	$	5,254	$	8,114	$	8,771	$	10,436

Stock-based compensation expense by type of award included within the consolidated statements of operations and comprehensive income (loss) was as follows:


	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2019		2018		2019		2018
	(in thousands)
Stock options	$	4,528	$	7,902	$	7,304	$	9,868
Restricted stock awards and units		668		163		1,351		457
Employee stock purchase plan awards		58		49		116		111
Total stock-based compensation expense	$	5,254	$	8,114		8,771		10,436

During the six months ended June 30, 2019, the Company entered into a consulting agreement (the “Sah Agreement”) with Dr. Dinah Sah, Ph.D., the Company’s former Chief Scientific Officer, pursuant to which Dr. Sah has agreed to provide consulting and advisory services, including but not limited to scientific guidance in connection with certain of the Company’s collaborations and research and development programs for a three-year period which commenced on June 28, 2019. In accordance with its terms, the Sah Agreement triggered an equity modification resulting in the recognition of $2.2 million of stock-based compensation expense related to the non-substantice service period of the Sah Agreement.

Restricted Stock Units

A summary of the status of and changes in unvested restricted stock unit activity under the Company’s equity award plans for the six months ended June 30, 2019 was as follows:


		Weighted
		Average
		Grant Date
		Fair Value
	Units	Per Unit
Unvested restricted stock units as of December 31, 2018	—		—
Granted	419,457	$	10.91
Vested	—		—
Forfeited	(16,675)	$	9.09
Unvested restricted stock units as of June 30, 2019	402,782	$	10.98

Stock-based compensation of restricted stock units is based on the fair value of the Company’s common stock on the date of grant and recognized over the vesting period. The weighted average fair value of restricted stock units granted to employees during the three and six months ended June 30, 2019 was $20.74 and $10.91 per share, respectively. The restricted stock units granted in the three and six months ended June 30, 2019 vest in equal amounts, annually over three years. There were no restricted stock units granted to employees in the three and six months ended June 30, 2018. The expense related to restricted stock units granted to employees was $0.7 million and $1.4 million for the three and six months ended June 30, 2019, respectively.

As of June 30, 2019, the Company had unrecognized stock-based compensation expense related to its unvested restricted stock units of $3.6 million, which is expected to be recognized over the remaining average vesting period of 2.6 years.

Stock Options

The following is a summary of stock option activity for the six months ended June 30, 2019:


		Weighted		Remaining	Aggregate
		Average		Contractual	Intrinsic
		Exercise		Life	Value
	Shares	Price		(in years)	(in thousands)
Outstanding at December 31, 2018	4,225,152	$	15.91
Granted	1,310,920	$	14.70
Exercised	(88,821)	$	11.24
Cancelled or forfeited	(207,716)	$	14.05
Outstanding at June 30, 2019	5,239,535	$	15.76	8.3	$	60,649
Exercisable at June 30, 2019	1,972,340	$	13.87	7.2	$	26,574
Vested and expected to vest at June 30, 2019	5,239,535	$	15.76	8.3	$	60,649

Using the Black‑Scholes option pricing model, the weighted-average fair value of options granted to employees and directors during the three and six months ended June 30, 2019 was $14.61 and $9.79 per share, respectively. The expense related to options granted to employees and directors was $4.5 million and $7.3 million for the three and six months ended June 30, 2019, respectively.

The weighted-average fair value of options granted to employees and directors during the three and six months ended June 30, 2018 was $13.88 and $15.92 per share, respectively. The expense related to awards granted to employees and directors was $7.9 million and $9.8 million for the three and six months ended June 30, 2018, respectively.

The fair value of each option issued to employees and directors was estimated at the date of grant using the Black-Scholes option pricing model with the following weighted-average assumptions:


	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2019		2018		2019		2018
Risk-free interest rate	2.2	%	2.8	%	2.4	%	2.7	%
Expected dividend yield	—	%	—	%	—	%	—	%
Expected term (in years)	6.0		6.0		6.0		6.0
Expected volatility	75.1	%	74.7	%	75.1	%	74.4	%

There were no new equity awards granted to non-employees during the three and six months ended June 30, 2019. The expense related to stock option awards previously granted to non‑employees was $0.1 million for the three and six months ended June 30, 2019. The expense related to awards previously granted to non-employees was $0.1 million and $0.2 million for the three and six months ended June 30, 2018, respectively.

As of June 30, 2019, the Company had unrecognized stock-based compensation expense related to its unvested stock options of $30.5 million which is expected to be recognized over the remaining weighted-average vesting period of 2.8 years.

Summary of significant accounting policies and basis of presentation (Policies)	6 Months Ended
	Jun. 30, 2019
Summary of significant accounting policies and basis of presentation
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements of the Company have been prepared in accordance with accounting principles generally accepted in the United States (“GAAP”) for interim financial reporting and as required by Regulation S-X, Rule 10-01. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. For further information, refer to the consolidated financial statements and footnotes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018 as filed with the Securities and Exchange Commission (“SEC”) on February 26, 2019. These interim condensed consolidated financial statements, in the opinion of management, reflect all normal recurring adjustments necessary for a fair presentation of the Company’s financial position and results of operations for the periods presented. Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASU”) of the Financial Accounting Standards Board (“FASB”). See “Recently Adopted Accounting Pronouncements” below for discussion of the Company’s adoption of new guidance effective January 1, 2019. All amounts and disclosures set forth in this Quarterly Report on Form 10-Q reflect adoption of these changes.
Principles of Consolidation	Principles of Consolidation The unaudited interim consolidated financial statements include the accounts of the Company and its wholly owned subsidiary as disclosed in Note 2, Summary of Significant Accounting Policies, within the “Notes to Consolidated Financial Statements” accompanying the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2018. Intercompany accounts and transactions have been eliminated.
Use of estimates	Use of Estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. On an ongoing basis, the Company’s management evaluates its estimates, which include, but are not limited to, estimates related to revenue recognition, accrued expenses, stock-based compensation expense, and income taxes. The Company bases its estimates on historical experience and other market specific or other relevant assumptions that it believes to be reasonable under the circumstances. Actual results may differ from those estimates or assumptions. Certain reclassifications have been made to prior periods to conform to current period presentation.
Leases	Leases Effective January 1, 2019, the Company accounted for its operating leases in accordance with ASC Topic 842 Leases (“ASC 842”). ASC 842 provides guidance on accounting for lease arrangements by both lessors and lessees and requires lessees to recognize a lease liability and a right-of-use asset for most leases. The Company determines if an arrangement is a lease at inception. The Company’s operating leases are included in operating lease right-of-use (“ROU”) assets, other current liabilities, and other non-current liabilities on the condensed consolidated balance sheets. ROU assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating lease ROU assets and liabilities are recognized at adoption date based on the present value of lease payments over the lease term. As the Company’s leases do not provide an implicit rate, an incremental borrowing rate was used based on the information available at the lease commencement date in determining the present value of lease payments. On future lease obligations, the implicit rate will be set when readily determinable. The operating lease ROU assets also include the effect of any lease payments made and exclude lease incentives. The Company’s lease terms may include options to extend or terminate the lease even when it is not reasonably certain that the option will be exercised. Lease expense for lease payments is recognized on a straight-line basis over the lease term. The Company has lease agreements with lease and non-lease components, which are accounted for separately. Non-lease components generally refer to common area maintenance charges related to the premises.
Revenue Recognition	Revenue Recognition The Company enters into collaboration agreements which are within the scope of ASC 606, Revenue from Contracts with Customers (“ASC 606”), under which the Company licenses rights to certain of the Company’s product candidates and performs research and development services. The terms of these arrangements typically include payment of one or more of the following: non-refundable, upfront fees; reimbursement of research and development costs; development, regulatory, and commercial milestone payments; and royalties on net sales of licensed products. Under ASC 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine the appropriate amount of revenue to be recognized for arrangements determined to be within the scope of ASC 606, the Company performs the following five steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect consideration it is entitled to in exchange for the goods or services it transfers to the customer. The promised goods or services in each arrangement typically consist of license rights to the Company’s intellectual property and research and development services. The Company provides options to additional items in the contracts, which are accounted for as separate contracts when the customer elects to exercise such options, unless the option provides a material right to the customer. The Company evaluates the customer options for material rights, or options to acquire additional goods or services for free or at a discount. If the customer options are determined to represent a material right, the material right is recognized as a separate performance obligation at the outset of the arrangement. Performance obligations are promised goods or services in a contract to transfer a distinct good or service to the customer and are considered distinct when (i) the customer can benefit from the good or service on its own or together with other readily available resources and (ii) the promised good or service is separately identifiable from other promises in the contract. In assessing whether promised goods or services are distinct, the Company considers factors such as the stage of development of the underlying intellectual property, the capabilities of the customer to develop the intellectual property on its own or whether the required expertise is readily available and whether the goods or services are integral or dependent to other goods or services in the contract. The Company estimates the transaction price based on the amount expected to be received for transferring the promised goods or services in the contract. The consideration may include fixed consideration or variable consideration. At the inception of each arrangement that includes variable consideration, the Company evaluates the amount of potential payments and the likelihood that the payments will be received. The Company utilizes either the most likely amount method or expected amount method to estimate the amount expected to be received based on which method best predicts the amount expected to be received. The amount of variable consideration which is included in the transaction price may be constrained, and is included in the transaction price only to the extent that it is probable that a significant reversal in the amount of the cumulative revenue recognized will not occur in a future period. The Company’s contracts often include development and regulatory milestone payments which are assessed under the most likely amount method and constrained if it is probable that a significant revenue reversal would occur. Milestone payments that are not within the Company’s control or the licensee’s control, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. At the end of each reporting period, the Company re-evaluates the probability of achievement of such development milestones and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect collaboration revenues in the period of adjustment. To date, the Company has not recognized any consideration related to the achievement of development, regulatory, or commercial milestones resulting from any of the Company’s collaboration arrangements. For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any consideration related to sales-based royalty revenue resulting from any of the Company’s collaboration arrangements. The Company allocates the transaction price based on the estimated stand-alone selling price of each of the performance obligations. The Company must develop assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract. The Company utilizes key assumptions to determine the stand-alone selling price for service obligations, which may include other comparable transactions, pricing considered in negotiating the transaction and the estimated costs. Additionally, in determining the standalone selling price for material rights, the Company utilizes comparable transactions, clinical trial success probabilities, and estimates of option exercise likelihood. Variable consideration is allocated specifically to one or more performance obligations in a contract when the terms of the variable consideration relate to the satisfaction of the performance obligation and the resulting amounts allocated are consistent with the amounts the Company would expect to receive for the satisfaction of each performance obligation. The consideration allocated to each performance obligation is recognized as revenue when control is transferred for the related goods or services. For performance obligations which consist of licenses and other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Upfront payments and fees are recorded as deferred revenue upon receipt or when due until the Company performs its obligations under these arrangements. Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional.
Stock-based Compensation Expense	Stock-based Compensation Expense The Company accounts for its stock-based compensation awards in accordance with ASC Topic 718 Compensation—Stock Compensation (“ASC 718”). ASC 718 requires all stock-based payments to employees, nonemployees, and directors, including grants of restricted stock units and stock options, to be recognized as expense in the statements of operations based on their grant date fair values. The Company estimates the fair value of options granted using the Black-Scholes option pricing model. The Company uses the fair value of its common stock on the grant date to determine the fair value of restricted stock units. The Black-Scholes option pricing model requires inputs based on certain subjective assumptions, including (a) the expected stock price volatility, (b) the calculation of expected term of the award, (c) the risk-free interest rate and (d) expected dividends. Due to a lack of company-specific historical and implied volatility data, the Company bases the estimate of expected volatility on the historical volatility of a group of similar companies that are publicly traded, blended with the most recent period of historic volatility of its common stock. The historical volatility is calculated based on a period of time commensurate with the expected term assumption. The computation of expected volatility is based on the historical volatility of a representative group of companies with similar characteristics to the Company, including stage of product development and life science industry focus. The Company uses the simplified method as prescribed by the SEC Staff Accounting Bulletin No. 107, Share-Based Payment, to calculate the expected term for stock options granted to employees as it does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term. For stock options granted to non-employees, the Company utilizes the contractual term of the arrangement as the basis for the expected term assumption. The risk-free interest rate is based on a treasury instrument whose term is consistent with the expected term of the stock options. The expected dividend yield is assumed to be zero as the Company has never paid dividends and has no current plans to pay any dividends on its common stock. The Company expenses the fair value of its stock-based compensation awards on a straight-line basis over the associated service period, which is generally the period in which the related services are received. The Company records the expense for stock-based compensation awards subject to performance conditions over the remaining service period when management determines that achievement of the performance condition is probable. Management evaluates if the achievement of a performance condition is probable based on the expected satisfaction of the performance conditions as of the reporting date.
Net Income (Loss) per Share	Net Income (Loss) per Share Basic net income (loss) per share is computed by dividing net income (loss) by the weighted-average number of common shares and restricted stock unit awards outstanding during the period. Diluted net income (loss) per share is computed using the weighted-average number of common shares and restricted stock unit awards outstanding during the period and, if dilutive, the weighted-average number of potential shares of common stock and restricted stock unit awards.
Recent Accounting Pronouncements	Recently Adopted Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, a comprehensive new lease accounting standard, which provides revised guidance on accounting for lease arrangements by both lessors and lessees and requires lessees to recognize a lease liability and a right-of-use asset for most leases. In July 2018, the FASB issued ASU No. 2018-11, Leases-Targeted Improvements (“ASC 842”), which provides an additional transition method that allowed entities to initially apply the new lease requirements at the adoption date, not the earliest period presented, and recognize a cumulative effect adjustment to the opening balance of retained earnings in the period of adoption. The Company elected this transition method at the adoption date of January 1, 2019. The Company elected a package of practical expedients, under which an entity need not reassess whether any expired or existing contracts are or contain leases, the lease classification for any expired or existing leases, or initial direct costs for any existing leases. The impact of adopting ASC 842 was represented as a capitalization of a right-of-use asset of approximately $31.0 million with a corresponding lease liability of approximately $36.7 million to be recognized over the remaining life of the Company’s leases. In June 2018, the FASB issued ASU No. 2018-07, Compensation-Stock Compensation: Improvements to Nonemployee Share-Based Payment Accounting (“ASU 2018-07”). The new standard largely aligns the accounting for share-based payment awards issued to employees and nonemployees by expanding the scope of ASC 718 to apply to nonemployee share-based transactions, as long as the transaction is not effectively a form of financing. The adoption of ASU 2018-07 on January 1, 2019 did not have a material impact on the Company's consolidated financial statements. Recent Accounting Pronouncements In August 2018, the FASB issued ASU No. 2018-13, Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement (“ASU 2018-13”). This standard eliminates, adds and modifies certain disclosure requirements for fair value measurements as part of its disclosure framework project. ASU 2018-13 is effective for annual reporting periods beginning after December 15, 2019 and interim periods within those annual periods and early adoption is permitted. The Company is currently evaluating the potential impact that this guidance may have on its consolidated financial statements. In June 2016, the FASB issued ASU No. 2016-13, Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”). ASU 2016-13 will change how companies account for credit losses for most financial assets and certain other instruments. For trade receivables, loans and held-to-maturity debt securities, companies will be required to recognize an allowance for credit losses rather than reducing the carrying value of the asset. ASU 2016-13 is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted. The Company is currently evaluating the potential impact that this guidance may have on its consolidated financial statements.

Fair value measurements (Tables)

6 Months Ended

Jun. 30, 2019

Fair value measurements

Assets and liabilities measured at fair value on a recurring basis

Assets and liabilities measured at fair value on a recurring basis as of June 30, 2019 and December 31, 2018 are as follows:


			Quoted Prices		Significant
			in Active		Other		Significant
			Markets for		Observable		Unobservable
			Identical Assets		Inputs		Inputs
Assets	Total		(Level 1)		(Level 2)		(Level 3)
June 30, 2019	(in thousands)
Money market funds included in cash and cash equivalents	$	79,108	$	79,108	$	—	$	—
Marketable securities:
U.S. Treasury notes		247,577		247,577		—		—
Equity securities		1,280		1,280		—		—
Total marketable securities	$	248,857	$	248,857	$	—	$	—
Warrants to purchase equity securities		414		—		414		—
Total	$	328,379	$	327,965	$	414	$	—
December 31, 2018
Money market funds included in cash and cash equivalents	$	46,173	$	46,173	$	—	$	—
Marketable securities:
U.S. Treasury notes		108,947		108,947		—		—
Equity securities		628		628		—		—
Total marketable securities	$	109,575	$	109,575	$	—	$	—
Warrants to purchase equity securities		234		—		234		—
Total	$	155,982	$	155,748	$	234	$	—

Schedule of fair value assumptions

The assumptions utilized to value the warrants to purchase equity securities as of June 30, 2019 and December 31, 2018 are as follows:


	As of June 30,		As of December 31,
	2019		2018
Risk-free interest rate	1.7	%	2.5	%
Expected dividend yield	—	%	—	%
Expected term (in years)	2.2		2.7
Expected volatility	88.8	%	112.7	%

Commitments and contingencies (Tables)

6 Months Ended

Jun. 30, 2019

Lessee, Operating Lease, Liability, Maturity [Table Text Block]


	Total Minimum
	Lease Payments
	(in thousands)
2019 (remainder of year)	$	2,756
2020		5,960
2021		6,138
2022		6,323
2023		6,512
2024+		20,897
Total future minimum lease payments	$	48,586
Less: imputed interest		(13,138)
Total lease liability	$	35,448
Reported as:
Other current liabilities	$	2,843
Other non-current liabilities		32,605
Total lease liability	$	35,448

Allocable arrangement consideration allocation


Performance Obligation	Amount
	(in thousands)
Research and Development Services for:
Huntington’s Program	$	14,228
Parkinson’s Program		6,040
Friedreich’s ataxia Program		14,821
Spinal Muscular Atrophy Program		29,116
Future Program		2,239
Committee Obligations:
AJSC		133
DAC		207
PD Material Right		7,855
Total	$	74,639

Schedule of allocation of transaction price


Performance Obligation	Amount
	(in thousands)
Research Services	$	34,482
First Development Option Material Right		34,518
Total	$	69,000

AbbVie Alpha Synuclein Collaboration Agreement

Schedule of allocation of transaction price


Performance Obligation	Amount
	(in thousands)
ASN Research Services	$	23,768
ASN First Development Option Material Right		41,232
Total	$	65,000

Schedule of allocation of fixed consideration


Performance Obligation	Amount
	(in thousands)
Fixed Consideration
AADC Program	$	80,373
FA Program		6,005
Discovery Program 1		3,002
Discovery Program 2		3,002
Total	$	92,382

Neurocrine Collaboration Agreement

Schedule of allocation of variable consideration


Performance Obligation	Amount
	(in thousands)
Variable Consideration
AADC Program	$	170,209
FA Program		114,023
Discovery Program 1		73,416
Discovery Program 2		73,416
Total	$	431,064

Stock based compensation (Tables)

6 Months Ended

Jun. 30, 2019

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Compensation cost recognized for all stock-based compensation awards

Total compensation cost recognized for all stock-based compensation awards in the statements of operations and comprehensive income (loss) is as follows:


	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2019		2018		2019		2018
	(in thousands)
Research and development	$	3,256	$	1,332	$	4,671	$	2,530
General and administrative		1,998		6,782		4,100		7,906
Total stock-based compensation expense	$	5,254	$	8,114	$	8,771	$	10,436

Summary of stock-based compensation expense by classification


	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2019		2018		2019		2018
	(in thousands)
Stock options	$	4,528	$	7,902	$	7,304	$	9,868
Restricted stock awards and units		668		163		1,351		457
Employee stock purchase plan awards		58		49		116		111
Total stock-based compensation expense	$	5,254	$	8,114		8,771		10,436

Summary of status and changes in unvested restricted stock

A summary of the status of and changes in unvested restricted stock unit activity under the Company’s equity award plans for the six months ended June 30, 2019 was as follows:


		Weighted
		Average
		Grant Date
		Fair Value
	Units	Per Unit
Unvested restricted stock units as of December 31, 2018	—		—
Granted	419,457	$	10.91
Vested	—		—
Forfeited	(16,675)	$	9.09
Unvested restricted stock units as of June 30, 2019	402,782	$	10.98

Summary of status and changes in stock options

The following is a summary of stock option activity for the six months ended June 30, 2019:


		Weighted		Remaining	Aggregate
		Average		Contractual	Intrinsic
		Exercise		Life	Value
	Shares	Price		(in years)	(in thousands)
Outstanding at December 31, 2018	4,225,152	$	15.91
Granted	1,310,920	$	14.70
Exercised	(88,821)	$	11.24
Cancelled or forfeited	(207,716)	$	14.05
Outstanding at June 30, 2019	5,239,535	$	15.76	8.3	$	60,649
Exercisable at June 30, 2019	1,972,340	$	13.87	7.2	$	26,574
Vested and expected to vest at June 30, 2019	5,239,535	$	15.76	8.3	$	60,649

Share-based Payment Arrangement, Employee

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Assumptions

The fair value of each option issued to employees and directors was estimated at the date of grant using the Black-Scholes option pricing model with the following weighted-average assumptions:


	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2019		2018		2019		2018
Risk-free interest rate	2.2	%	2.8	%	2.4	%	2.7	%
Expected dividend yield	—	%	—	%	—	%	—	%
Expected term (in years)	6.0		6.0		6.0		6.0
Expected volatility	75.1	%	74.7	%	75.1	%	74.4	%

Right-of-use asset and lease liabilities (Details) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Apr. 30, 2014 item	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Lease, Practical Expedients, Package [true false]				true
Lessee, Operating Lease, Existence of Option to Extend [true false]				true
Rent expense		$ 1,600	$ 1,000	$ 3,000	$ 1,800
Restricted cash included in deposits and other noncurrent assets		$ 735		$ 735		$ 735
Weighted average remaining lease term		7 years 4 months 24 days		7 years 4 months 24 days
Weighted average incremental borrowing rate		8.5		8.5
Total minimum lease payments
2019 (remainder)		$ 2,756		$ 2,756
2020		5,960		5,960
2021		6,138		6,138
2022		6,323		6,323
2023		6,512		6,512
2024+		20,897		20,897
Total		48,586		48,586
Less: imputed interest		(13,138)		(13,138)
Total lease liability		35,448		35,448
Current lease liabilities		$ 2,843		$ 2,843
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]		Other Liabilities, Current		Other Liabilities, Current
Non-current lease liabilities		$ 32,605		$ 32,605
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]		Other non-current liabilities		Other non-current liabilities
75 Sidney Street
Number of renewal options \| item	2
Term of each renewal option	5 years
Leasehold improvements		$ 1,300		$ 1,300
Entitled leasehold improvements		300		300
64 Sidney Street
Leasehold improvements		$ 3,500		$ 3,500

Commitments and contingencies - Neurocrine Collaboration Agreement - (Details) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($) $ / shares	Mar. 31, 2019 USD ($) item shares	Jun. 30, 2019 USD ($) $ / shares shares
Neurocrine \| FA Program
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage of profit or loss under co-co option after paying rate-shifting fee		60.00%
Neurocrine Collaboration Agreement \| AADC
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage of profit or loss under co-co option		50.00%
Percentage of profit or loss under co-co option after paying rate-shifting fee		45.00%
Neurocrine Collaboration Agreement \| FA Program
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage of profit or loss under co-co option after paying rate-shifting fee		40.00%
Neurocrine Collaboration Agreement \| Neurocrine
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of collaboration programs \| item		4
Number of discovery programs \| item		2
Number of targets \| item		8
Upfront payment		$ 115,000	$ 115,000
Purchase of common stock, shares \| shares		4,179,728	4,179,728
Purchase of common stock		$ 50,000	$ 5,000
Price per share \| $ / shares	$ 11.9625		$ 11.9625
Estimated cost reimbursement			$ 431,100
Termination period		10 years
Period of advance notice for termination prior to first commercial sale		180 days
Period of advance notice for termination after first commercial sale		1 year
Discount related to equity investment			27,600
Equity investment	$ 50,000		50,000
Allocation of Transaction Price
Allocation of variable consideration	431,064		431,064
Allocation of fixed consideration	92,382		92,382
Revenue recognized	12,500		14,400
Deferred revenue	88,000		88,000
Reimbursement costs expected to be received	10,100		10,100
Costs to obtain collaboration agreement	800		800
Consideration received			5,000
Neurocrine Collaboration Agreement \| Neurocrine \| Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage of reduction in royalty payments		50.00%
Neurocrine Collaboration Agreement \| Neurocrine \| AADC
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage of profit or loss under co-co option		50.00%
Rate-shifting fee		$ 35,000
Percentage of profit or loss under co-co option after paying rate-shifting fee		55.00%
Allocation of Transaction Price
Allocation of variable consideration	170,209		170,209
Allocation of fixed consideration	80,373		80,373
Neurocrine Collaboration Agreement \| Neurocrine \| FA Program
Allocation of Transaction Price
Allocation of variable consideration	114,023		114,023
Allocation of fixed consideration	6,005		6,005
Neurocrine Collaboration Agreement \| Neurocrine \| Discovery program 1
Allocation of Transaction Price
Allocation of variable consideration	73,416		73,416
Allocation of fixed consideration	3,002		3,002
Neurocrine Collaboration Agreement \| Neurocrine \| Discovery program 2
Allocation of Transaction Price
Allocation of variable consideration	73,416		73,416
Allocation of fixed consideration	$ 3,002		$ 3,002
Neurocrine Collaboration Agreement \| Neurocrine \| Development and regulatory milestones \| AADC
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate maximum milestone payments to be received from collaborative partner		$ 170,000
Neurocrine Collaboration Agreement \| Neurocrine \| Development and regulatory milestones \| FA Program
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate maximum milestone payments to be received from collaborative partner		195,000
Neurocrine Collaboration Agreement \| Neurocrine \| Development and regulatory milestones \| Discovery program 1
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate maximum milestone payments to be received from collaborative partner		130,000
Neurocrine Collaboration Agreement \| Neurocrine \| Commercial Milestone
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Per Milestone, maximum milestone payments to be received from collaborative partner		275,000
Aggregate maximum milestone payments to be received from collaborative partner		$ 1,100,000

Stock based compensation (Details)					1 Months Ended		3 Months Ended		6 Months Ended		12 Months Ended
Stock based compensation (Details)	Jan. 01, 2019 shares	Jan. 01, 2018 shares	Jan. 01, 2017 shares	Jan. 01, 2016 shares	Oct. 31, 2015 shares	Jan. 31, 2014 $ / shares shares	Jun. 30, 2019 USD ($) item $ / shares shares	Jun. 30, 2018 USD ($) shares	Jun. 30, 2019 USD ($) item $ / shares shares	Jun. 30, 2018 USD ($) shares	Dec. 31, 2016 item	Dec. 31, 2018 $ / shares	Aug. 31, 2015 shares	Apr. 30, 2015 shares	Aug. 31, 2014 shares	Apr. 30, 2014 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation \| $							$ 5,254,000	$ 8,114,000	$ 8,771,000	$ 10,436,000
Stock options granted (in shares)									1,310,920
Exercise price \| $ / shares							$ 15.76		$ 15.76			$ 15.91
Granted (in dollars per share) \| $ / shares									$ 14.70
2014 Stock Option and Grant Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized for stock-based compensation plan (in shares)					2,998,823	823,529							2,669,411	2,047,058	2,000,000	1,411,764
2015 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares authorized for issuance	325,707	321,300	267,658	267,492
Number of shares authorized for stock-based compensation plan (in shares)					262,362
Period to purchase shares									6 months
Increase in ESSP shares (as a percent)									1.00%
2015 Employee Stock Purchase Plan \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Payroll deduction percentage					1.00%
2015 Employee Stock Purchase Plan \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Payroll deduction percentage					10.00%
2015 Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future issuance (in shares)					1,311,812		2,166,946		2,166,946
Percentage limit of issued and outstanding shares up to which additional shares may be issued									4.00%
Common stock shares authorized for issuance	1,302,830	1,285,200	1,070,635	1,069,971
Inducement Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of executives issued awards \| item							2		2
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation \| $							$ 4,528,000	7,902,000	$ 7,304,000	9,868,000
Stock options \| Inducement Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
New stock options issued									58,125
Vesting period									4 years
Stock options \| Inducement Awards \| Vesting period, tranche one
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage									25.00%
Stock options \| Inducement Awards \| Vesting period, tranche two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period									36 months
Vesting percentage									75.00%
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation \| $							668,000	$ 163,000	$ 1,351,000	$ 457,000
Unrecognized stock-based compensation expense \| $							$ 3,600,000		$ 3,600,000
Granted (in shares)								0	419,457	0
Restricted stock granted, original issued price (in dollars per share) \| $ / shares							$ 20.74		$ 10.91
Restricted stock units \| 2015 Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock granted (in shares)							65,052		419,457
Restricted stock units \| Inducement Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period									3 years
Restricted stock units \| Inducement Awards \| Vesting period, tranche one
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage									33.00%
Restricted stock units \| Inducement Awards \| Vesting period, tranche two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage									33.00%
Restricted stock units \| Inducement Awards \| Vesting period, tranche three
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage									33.00%
Performance based milestone awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Probable performance milestones \| item											1
Performance milestones \| item											3
Stock-based compensation \| $								$ 100,000	$ 0	$ 300,000
Compensation expense for remaining founders' awards \| $									$ 0
Founders restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock granted (in shares)						1,188,233
Restricted stock granted, original issued price (in dollars per share) \| $ / shares						$ 0.0425
Number of awards \| item							2		2
Founders restricted stock \| Vesting period, tranche one
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock granted (in shares)						835,292
Founders restricted stock \| Vesting period, tranche two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock granted (in shares)						352,941
Founders restricted stock \| Minimum \| Vesting period, tranche one
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period						1 year
Founders restricted stock \| Maximum \| Vesting period, tranche one
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period						4 years
Non-statutory stock options \| Inducement Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
New stock options issued							338,750
Share-based Payment Arrangement, Employee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation \| $							$ 4,500,000		$ 7,300,000
Share-based Payment Arrangement, Employee \| 2014 Stock Option and Grant Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period									4 years
Vesting percentage									75.00%
Share-based Payment Arrangement, Employee \| 2014 Stock Option and Grant Plan \| Vesting period, tranche one
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period									1 year
Vesting percentage									25.00%
Share-based Payment Arrangement, Employee \| 2014 Stock Option and Grant Plan \| Vesting period, tranche two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period									3 years
Share-based Payment Arrangement, Employee \| 2015 Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
New stock options issued							557,580		1,310,920
Share-based Payment Arrangement, Employee \| Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation \| $								7,900,000		9,800,000
Share-based Payment Arrangement, Employee \| Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation \| $							$ 700		$ 1,400,000
Share-based Payment Arrangement, Nonemployee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted (in shares)							0		0
Share-based Payment Arrangement, Nonemployee \| 2014 Stock Option and Grant Plan \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period									1 year
Share-based Payment Arrangement, Nonemployee \| 2014 Stock Option and Grant Plan \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period									4 years
Share-based Payment Arrangement, Nonemployee \| 2015 Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
New stock options issued							0		0
Share-based Payment Arrangement, Nonemployee \| Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation \| $							$ 100,000	100,000	$ 100,000	200,000
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation \| $							3,256,000	1,332,000	4,671,000	2,530,000
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation \| $							$ 1,998,000	$ 6,782,000	$ 4,100,000	$ 7,906,000

Stock based compensation - Stock Options - (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding, beginning balance (in shares)			4,225,152
Granted (in shares)			1,310,920
Exercised (in shares)			(88,821)
Cancelled or forfeited (in shares)			(207,716)
Outstanding, ending balance (in shares)	5,239,535		5,239,535
Exercisable (in shares)	1,972,340		1,972,340
Vested and expected to vest (in shares)	5,239,535		5,239,535
Weighted Average Exercise Price
Outstanding (in dollars per share)			$ 15.91
Granted (in dollars per share)			14.70
Exercised (in dollars per share)			11.24
Cancelled or forfeited (in dollars per share)			14.05
Outstanding (in dollars per share)	$ 15.76		15.76
Exercisable (in dollars per share)	13.87		13.87
Vested and expected to vest (in dollars per share)	$ 15.76		$ 15.76
Remaining Contractual Life
Outstanding			8 years 3 months 18 days
Exercisable			7 years 2 months 12 days
Vested and expected to vest			8 years 3 months 18 days
Aggregate Intrinsic Value
Outstanding	$ 60,649		$ 60,649
Exercisable	26,574		26,574
Vested and expected to vest	60,649		60,649
Options disclosures
Stock-based compensation	5,254	$ 8,114	8,771	$ 10,436
Stock options
Options disclosures
Stock-based compensation	$ 4,528	$ 7,902	$ 7,304	$ 9,868
Share-based Payment Arrangement, Employee
Options disclosures
Weighted average fair value of grants (in dollars per share)	$ 14.61	$ 13.88	$ 9.79	$ 15.92
Stock-based compensation	$ 4,500		$ 7,300
Share-based Payment Arrangement, Employee \| Stock options
Options disclosures
Stock-based compensation		$ 7,900		$ 9,800
Share-based Payment Arrangement, Nonemployee
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Granted (in shares)	0		0
Share-based Payment Arrangement, Nonemployee \| Stock options
Options disclosures
Stock-based compensation	$ 100	$ 100	$ 100	$ 200

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2019	Dec. 31, 2018
Condensed Consolidated Balance Sheets
Preferred Stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred Stock, Shares Authorized	5,000,000	5,000,000
Preferred Stock, Shares Issued	0	0
Preferred Stock, Shares Outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common Stock, Shares Authorized	120,000,000	120,000,000
Common Stock, Shares, Issued	36,677,608	32,364,895
Common Stock, Shares, Outstanding	36,677,608	32,364,895

Nature of business (Details) - USD ($) $ in Thousands	6 Months Ended
Nature of business (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Nature of business
Accumulated deficit	$ (285,068)	$ (269,051)
Proceeds raised	640,000
Cash, cash equivalents, and marketable debt securities	$ 327,500

Summary of significant accounting policies and basis of presentation (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, right-of-use asset	$ 30,041
Operating lease liability	$ 35,448
ASU 2016-02 \| Restatement Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, right-of-use asset		$ 31,000
Operating lease liability		$ 36,700

Cash, cash equivalents, and available-for-sale marketable securities (Details) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Amortized Cost
Cash and cash equivalents	$ 79,885,000	$ 46,859,000
Total marketable securities, amortized cost	248,568,000	110,171,000
Total money market funds and marketable securities	327,676,000	156,344,000
Fair Value
Total marketable securities	248,857,000	109,575,000
Total money market funds and marketable securities	327,965,000	155,748,000
Unrealized Gains and Losses
Total marketable securities, unrealized gains	290,000	1,000
Total money market funds and marketable securities	290,000	1,000
Total marketable securities, unrealized losses	1,000	597,000
Total money market funds and marketable securities	1,000	597,000
Other than temporary losses	$ 0
Maximum
Unrealized Gains and Losses
Debt securities, contractual maturity period	1 year
Money market funds
Amortized Cost
Cash and cash equivalents	$ 79,108,000	46,173,000
U.S. Treasury notes
Amortized Cost
Marketable securities, amortized cost	247,348,000	108,951,000
Fair Value
Marketable debt securities, fair value	247,577,000	108,947,000
Unrealized Gains and Losses
Marketable securities, unrealized gains	230,000	1,000
Marketable securities, unrealized losses	1,000	5,000
Equity securities
Amortized Cost
Marketable equity securities, amortized cost	1,220,000	1,220,000
Fair Value
Marketable equity securities, fair value	1,280,000	628,000
Unrealized Gains and Losses
Equity securitiess, unrealized gains	$ 60,000
Equity securitiess, unrealized losses		$ 592,000

Accrued expenses (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Accrued expenses
Research and development costs	$ 6,908	$ 3,555
Employee compensation costs	2,319	3,780
Professional services	1,301	1,448
Accrued goods and services	976	784
Patent costs	162	120
Other	116	101
Total	$ 11,782	$ 9,788

Fair value measurements - Assets measured on a recurring basis - (Details) $ in Thousands	Jun. 30, 2019 USD ($) item	Dec. 31, 2018 USD ($) item
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	$ 79,885	$ 46,859
Measurement Input, Risk-Free Interest Rate
Fair value assumptions
Warrants, measurement input \| item	0.017	0.025
Measurement Input, Expected Term
Fair value assumptions
Warrants, measurement input \| item	2.2	2.7
Measurement Input, Expected Volatility
Fair value assumptions
Warrants, measurement input \| item	0.888	1.127
Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Marketable securities	$ 248,857	$ 109,575
Total assets measured at fair value	328,379	155,982
Level 1 \| Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Marketable securities	248,857	109,575
Total assets measured at fair value	327,965	155,748
Level 2 \| Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Total assets measured at fair value	414	234
U.S. Treasury notes \| Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Marketable securities	247,577	108,947
U.S. Treasury notes \| Level 1 \| Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Marketable securities	247,577	108,947
Equity securities \| Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Marketable securities	1,280	628
Equity securities \| Level 1 \| Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Marketable securities	1,280	628
Warrants to purchase equity securities \| Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Warrants to purchase equity securities	414	234
Warrants to purchase equity securities \| Level 2 \| Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Warrants to purchase equity securities	414	234
Money market funds
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	79,108	46,173
Money market funds \| Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	79,108	46,173
Money market funds \| Level 1 \| Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	$ 79,108	$ 46,173

Other liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Other liabilities
Lease liability	$ 2,843
Total other current liabilities	2,843
Non-current lease liabilities	32,605
Deferred rent		$ 5,710
Other	1,001	1,001
Total other non-current liabilities	$ 33,606	$ 6,711

Commitments and contingencies - Significant Agreements - (Details) - Sanofi Genzyme - USD ($) $ in Millions		1 Months Ended
	Jun. 14, 2019	Oct. 31, 2017	Feb. 28, 2015
Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Non-refundable upfront payment received			$ 65.0
Premium over fair value on temporary equity issued			5.0
Per Milestone, maximum milestone payments to be received from collaborative partner		$ 540.0
Up-front fee paid on date of termination	$ 10.0
Milestone payable upon achievement	10.0
Collaborative Arrangement \| Regulatory approval milestone
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate maximum milestone payments to be received from collaborative partner		220.0
Collaborative Arrangement \| Regulatory approval milestone \| Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Per Milestone, maximum milestone payments to be received from collaborative partner		40.0
Collaborative Arrangement \| Regulatory approval milestone \| Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Per Milestone, maximum milestone payments to be received from collaborative partner		50.0
Collaborative Arrangement \| Commercial Milestone
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate maximum milestone payments to be received from collaborative partner		320.0
Collaborative Arrangement \| Commercial Milestone \| Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Per Milestone, maximum milestone payments to be received from collaborative partner		50.0
Collaborative Arrangement \| Commercial Milestone \| Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Per Milestone, maximum milestone payments to be received from collaborative partner		100.0
Termination Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Non-refundable upfront payment received	1.0
Huntington's Program
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Milestone payable upon achievement	$ 10.0
Parkinson's Program \| Regulatory and commercial milestone
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Milestone payments no longer receivable		$ 105.0
Spinal Muscular Atrophy Program
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Maximum potential in-kind services to be provided by collaborative partner			5.0
Option exercise payment required from collaborative partner for each program specified			30.0
Split Territory Program
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Option exercise payment required from collaborative partner for each program specified			$ 20.0
Redeemable Convertible Preferred Stock Series B \| Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Temporary equity issued (in shares)			10,000,000
Temporary equity issued			$ 30.0
Fair value of temporary equity issued			25.0
Premium over fair value on temporary equity issued			$ 5.0

Commitments and contingencies - Termination of Agreement (Details) - Termination Agreement - Sanofi Genzyme $ in Millions	Jun. 14, 2019 USD ($) item
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of non central nervous system \| item	2
Up-front payment made	$ 10.0
Milestone payment agreed to be paid	$ 10.0
Period in which milestone payment will be made of filing of investigational new drug	15 days
Percentage of threshold sublicensing income agreed to be paid	50.00%
Unused in-kind services waived	$ 0.4
Threshold number of capsids having exclusive options to evaluate for no consideration \| item	4
Threshold additional number of capsids having options to evaluate for low six-figure payment per capsid \| item	2
Threshold number of capsids that has right to obtain an exclusive license \| item	2
Option exercise fee	$ 1.0
Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
AAV capsids to license \| item	1
Development and regulatory milestones
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Milestone payable upon achievement	$ 15.0
Sales milestone
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Milestone payable upon achievement	$ 20.0

Commitments and contingencies - Accounting Analysis - (Details)		1 Months Ended		3 Months Ended		6 Months Ended
	Jun. 14, 2019 USD ($)	Feb. 28, 2019 USD ($)	Feb. 28, 2015 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) item	Jun. 30, 2018 USD ($)
Allocable arrangement consideration allocation
Committee Obligations: Alliance Joint Steering Committee ("AJSC")			$ 133,000
Committee Obligations: Development Advisory Committee ("DAC")			207,000
PD Material Right			7,855,000
Total allocable arrangement consideration allocations.			74,639,000
Huntington's Program
Allocable arrangement consideration allocation
Research and development services			14,228,000
Parkinson's Program
Allocable arrangement consideration allocation
Research and development services			6,040,000
Friedreich's ataxia Program
Allocable arrangement consideration allocation
Research and development services			14,821,000
Spinal Muscular Atrophy Program
Allocable arrangement consideration allocation
Research and development services			29,116,000
Future Program
Allocable arrangement consideration allocation
Research and development services			2,239,000
Sanofi Genzyme \| Huntington's Program
Income Statement Related Disclosures [Abstract]
Deferred revenue	$ 10,000,000.0
Milestone payable upon achievement	10,000,000.0
Sanofi Genzyme \| Collaborative Arrangement
Allocable arrangement consideration
Collaborative Arrangement Nonredeemable Up Front Fee Received			65,000,000.0
Additional consideration, premium over fair value on temporary equity issued			5,000,000.0
In-kind services and other funding to be provided by collaborative partner			4,600,000
Total allocable arrangement consideration			$ 74,600,000
Allocable arrangement consideration allocation
Additional option exercise payments			0
Income Statement Related Disclosures [Abstract]
Revenue recognized	28,700,000			$ 1,500,000	$ 700,000	$ 2,900,000	$ 1,200,000
Deferred revenue	48,700,000
Up-front fee paid on date of termination	10,000,000.0
Milestone payable upon achievement	10,000,000.0
Total payable amount	20,000,000.0
Sanofi Genzyme \| Termination Agreement
Allocable arrangement consideration
Collaborative Arrangement Nonredeemable Up Front Fee Received	$ 1,000,000.0
Income Statement Related Disclosures [Abstract]
Revenue recognized				30,200,000		31,600,000
Deferred revenue				10,000,000.0		10,000,000.0
AbbVie \| Collaborative Arrangement
Income Statement Related Disclosures [Abstract]
Revenue recognized						4,900,000
Deferred revenue				57,100,000		57,100,000
AbbVie \| AbbVie Alpha Synuclein Collaboration Agreement
Allocable arrangement consideration
Collaborative Arrangement Nonredeemable Up Front Fee Received		$ 65,000,000.0
Income Statement Related Disclosures [Abstract]
Revenue recognized				200,000		400,000
Deferred revenue				$ 64,600,000		$ 64,600,000
Number of development options \| item						4
Redeemable Convertible Preferred Stock Series B \| Sanofi Genzyme \| Collaborative Arrangement
Allocable arrangement consideration
Additional consideration, premium over fair value on temporary equity issued			$ 5,000,000.0

Commitments and contingencies - AbbVie Tau Collaboration Agreement - (Details) - AbbVie Tau Collaboration Agreement - AbbVie $ in Thousands	1 Months Ended	3 Months Ended	6 Months Ended
	Feb. 28, 2018 USD ($) item	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) item	Jun. 30, 2018 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Non-refundable upfront payment received	$ 69,000
First Research Compound payment	80,000
Two additional research compounds payment to be received for each	$ 30,000
Number of additional research compounds \| item	2
One-time payment upon exercise of license option	$ 75,000
Milestone payments to be received for licensed compound in case Alzheimer disease indication	550,000
Milestone payments to be received for licensed compound in case first indication other than Alzheimer disease	230,000
Milestone payments to be received for licensed compound for subsequent non-Alzheimer disease indication	$ 115,000
Number of development options \| item	3		3
Number of research antibodies \| item	1
Revenue recognized		$ 1,900	$ 3,200	$ 2,300
Allocation of Transaction Price
Allocation of Transaction Price			69,000
Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Antibodies to include in Research Period \| item	2
The number of Licensed Products \| item	1
Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of antibodies encoded by virus \| item	5
Antibodies to include in Research Period \| item	3
Research Services
Allocation of Transaction Price
Allocation of Transaction Price			34,482
First Development Option Material Right
Allocation of Transaction Price
Allocation of Transaction Price			$ 34,518

Commitments and contingencies - AbbVie Alpha Synuclein Collaboration Agreement - (Details) - AbbVie Alpha Synuclein Collaboration Agreement - AbbVie $ in Thousands	1 Months Ended	3 Months Ended	6 Months Ended
	Feb. 28, 2019 USD ($) item	Jun. 30, 2019 USD ($)	Jun. 30, 2019 USD ($) item
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of antibodies encoded by virus \| item	1
Number of research antibodies \| item	1
Non-refundable upfront payment received	$ 65,000
First Research Compound payment	80,000
Three additional research compounds payment to be received for each	$ 30,000
Number of additional research compounds \| item	3
Milestone payments to be received for licensed compound in case Parkinson's disease indication	$ 450,000
Milestone payments to be received for licensed compound in case first indication other than Parkinson's disease	185,000
Milestone payments to be received for licensed compound for subsequent non-Parkinson's disease indication	$ 92,500
Binds to alpha-synuclein protein, after the termination date (in months)	18 months
Number of development options \| item			4
Deferred revenue		$ 64,600	$ 64,600
Revenue recognized		$ 200	$ 400
Allocation of Transaction Price
Allocation of Transaction Price	$ 65,000
Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Antibodies to include in Research Period \| item	1
The number of Licensed Products \| item	1
Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Antibodies to include in Research Period \| item	4
Research Services
Allocation of Transaction Price
Allocation of Transaction Price	$ 23,768
First Development Option Material Right
Allocation of Transaction Price
Allocation of Transaction Price	41,232
Commercial Milestone
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Specified commercial milestone payments	$ 500,000

Commitments and contingencies - Other Agreements - (Details) $ in Thousands	6 Months Ended	12 Months Ended	42 Months Ended
	Jun. 30, 2019 USD ($)	Dec. 31, 2016 USD ($) multiple	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2016 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Non-current liability	$ 33,606		$ 33,606	$ 6,711
Various contract research organizations and institutions
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Milestone payable upon achievement	$ 100
Various contract research organizations and institutions \| Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of days written notice required by reporting entity to terminate agreement			30 days
Various contract research organizations and institutions \| Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of days written notice required by reporting entity to terminate agreement			90 days
Non-profit organization agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Maximum funding		$ 4,000
Funding multiple \| multiple		2.6
Milestone payment liability					$ 1,000
Non-current liability					$ 1,000
MRIC
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Amount of investment						$ 2,000

Preferred stock (Details) - shares	Jun. 30, 2019	Dec. 31, 2018
Preferred stock
Preferred stock, authorized	5,000,000	5,000,000

Net income (loss) per share (Details) - shares	3 Months Ended		6 Months Ended
Net income (loss) per share (Details) - shares	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	4,547,272	7,048,006	5,877,611	7,048,006
Restricted common stock awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	235,294	347,724	235,294	347,724
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	154,781		402,782
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	4,157,197	6,700,282	5,239,535	6,700,282