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Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2019	Feb. 28, 2020	Jun. 28, 2019
Document and Entity Information
Document Type	10-K
Document Annual Report	true
Document Transition Report	false
Document Period End Date	Dec. 31, 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
Title of 12(b) Security	Common Stock, $0.001 par value
Trading Symbol	VYGR
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Shell Company	false
Entity Central Index Key	0001640266
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Entity Public Float			$ 686.3
Entity Common Stock, Shares Outstanding		37,153,159

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 86,042	$ 46,859
Marketable securities, current	195,491	108,947
Collaboration receivable	18,496
Prepaid expenses and other current assets	4,630	6,675
Total current assets	304,659	162,481
Property and equipment, net	17,986	12,771
Deposits and other non-current assets	1,723	1,149
Marketable securities, non-current	1,920	628
Operating lease, right-of-use asset	28,472
Total assets	354,760	177,029
Current liabilities:
Accounts payable	4,070	1,038
Accrued expenses	21,516	9,788
Other current liabilities	3,193
Deferred revenue, current	47,233	20,847
Total current liabilities	76,012	31,673
Deferred revenue, non-current	147,260	92,199
Other non-current liabilities	31,976	6,711
Total liabilities	255,248	130,583
Commitments and contingencies (see note 9)
Stockholders' equity:
Preferred stock, $0.001 par value: 5,000,000 shares authorized; no shares issued and outstanding at December 31, 2019 and 2018
Common stock, $0.001 par value: 120,000,000 shares authorized; 36,865,116 and 32,364,895 shares issued and outstanding at December 31, 2019 and 2018, respectively	37	32
Additional paid-in capital	412,227	315,598
Accumulated other comprehensive loss	(104)	(133)
Accumulated deficit	(312,648)	(269,051)
Total stockholders' equity	99,512	46,446
Total liabilities and stockholders' equity	$ 354,760	$ 177,029

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Consolidated Statements of Operations and Comprehensive Loss
Collaboration revenue	$ 104,391	$ 7,619	$ 10,135
Operating expenses:
Research and development	119,735	64,905	62,260
General and administrative	36,335	33,809	19,738
Total operating expenses	156,070	98,714	81,998
Operating loss	(51,679)	(91,095)	(71,863)
Other income (expense), net:
Interest income	6,457	3,310	1,227
Other income (expense), net	1,625	(683)	(62)
Total other income	8,082	2,627	1,165
Loss before income taxes	(43,597)	(88,468)	(70,698)
Income tax benefit		180
Net loss	(43,597)	(88,288)	(70,698)
Other comprehensive income (loss)
Net unrealized gain (loss) on available-for-sale-securities	29	34	(235)
Total other comprehensive income (loss)	29	34	(235)
Comprehensive loss	$ (43,568)	$ (88,254)	$ (70,933)
Net loss per share, basic and diluted	$ (1.21)	$ (2.75)	$ (2.64)
Weighted-average common shares outstanding, basic and diluted	35,898,266	32,065,781	26,803,711

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, 2016	$ 26	$ 225,963	$ (52)	$ (90,015)	$ 135,922
Shares, Outstanding, Beginning Balance at Dec. 31, 2016	25,597,912
Vesting of restricted stock	$ 1	12			13
Vesting of restricted stock (in shares)	573,803
Exercises of vested stock options		1,363			1,363
Exercises of vested stock options (in shares)	158,677
Issuance of common stock under ESPP		563			563
Issuance of common stock under ESPP (in shares)	66,652
Issuance of common stock from public offering (net of underwriters discounts and issuance costs of $4,100)	$ 5	57,989			57,994
Stock Issued During Period, Shares, New Issues	5,175,000
Stock based compensation expense		9,129			9,129
Unrealized gain (loss) on available for-sale securities, net of tax			(235)		(235)
Net loss				(70,698)	(70,698)
Stockholders' Equity, Ending Balance at Dec. 31, 2017	$ 32	295,019	(287)	(160,713)	134,051
Shares, Outstanding, Ending Balance at Dec. 31, 2017	31,572,044
Vesting of restricted stock		9			9
Vesting of restricted stock (in shares)	319,891
Exercises of vested stock options		3,891			3,891
Exercises of vested stock options (in shares)	384,186
Issuance of common stock under ESPP		969			969
Issuance of common stock under ESPP (in shares)	88,774
Stock based compensation expense		15,710			15,710
Unrealized gain (loss) on available for-sale securities, net of tax			34		34
Impact of adopting new accounting standards \| ASU 2016-01			120	(120)
Impact of adopting new accounting standards \| ASU 2014-09				(19,930)	(19,930)
Impact of adopting new accounting standards					(20,050)
Net loss				(88,288)	(88,288)
Stockholders' Equity, Ending Balance at Dec. 31, 2018	$ 32	315,598	(133)	(269,051)	46,446
Shares, Outstanding, Ending Balance at Dec. 31, 2018	32,364,895
Exercises of vested stock options	$ 1	2,713			$ 2,714
Exercises of vested stock options (in shares)	250,276				250,276
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
Issuance of common stock under ESPP		663			663
Issuance of common stock under ESPP (in shares)	70,217
Stock based compensation expense		15,640			15,640
Unrealized gain (loss) on available for-sale securities, net of tax			29		29
Net loss				(43,597)	(43,597)
Stockholders' Equity, Ending Balance at Dec. 31, 2019	$ 37	$ 412,227	$ (104)	$ (312,648)	$ 99,512
Shares, Outstanding, Ending Balance at Dec. 31, 2019	36,865,116

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flow from operating activities
Net loss	$ (43,597)	$ (88,288)	$ (70,698)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Stock-based compensation expense	15,640	15,710	9,238
Depreciation	2,765	2,117	1,595
Amortization of premiums and discounts on marketable securities	(3,584)	(2,163)	(24)
In-kind research and development expenses	616	176	113
Other non-cash items	(1,612)	859	46
Changes in operating assets and liabilities:
Collaboration receivable	(18,496)
Prepaid expenses and other current assets	1,675	(3,937)	1,630
Operating lease, right-of-use asset	2,951
Other non-current assets	(343)	(180)	1,000
Accounts payable	2,598	(282)	470
Accrued expenses	11,728	(1,600)	4,900
Operating lease liabilities	(2,506)
Lease incentive benefit		321	515
Deferred revenue	80,831	61,380	(10,135)
Net cash provided by (used in) operating activities	48,666	(15,887)	(61,350)
Cash flow from investing activities
Purchases of property and equipment	(7,718)	(4,305)	(3,985)
Proceeds from sale of equipment	172
Purchases of marketable securities	(494,231)	(333,228)	(147,296)
Proceeds from maturities or sales of marketable securities	411,300	364,000	147,600
Net cash (used in) provided by investing activities	(90,477)	26,467	(3,681)
Cash flow from financing activities
Proceeds from the issuance of common stock in connection with the Neurocrine Collaboration Agreement, net	77,617
Proceeds from the issuance of common stock net of discount and issuance costs			57,994
Proceeds from the exercise of stock options	2,714	3,889	1,363
Proceeds from the purchase of common stock under ESPP	663	860	563
Net cash provided by financing activities	80,994	4,749	59,920
Net increase in cash and cash equivalents	39,183	15,329	(5,111)
Cash, cash equivalents, and restricted cash beginning of period	47,594	32,265	37,376
Cash, cash equivalents, and restricted cash end of period	86,777	47,594	$ 32,265
Supplemental disclosure of cash and non-cash activities
Impact of adopting new accounting standards		20,050
Operating lease right-of-use assets obtained in exchange for operating lease liabilities	30,964
Capital expenditures incurred but not yet paid	$ 434	300
ASU 2014-09
Supplemental disclosure of cash and non-cash activities
Impact of adopting new accounting standards		$ 19,930

Summary of significant accounting policies

12 Months Ended

Dec. 31, 2019

Summary of significant accounting policies

Summary of significant accounting policies

2. Summary of significant accounting policies

The following is a summary of significant accounting policies followed in the preparation of these financial statements.

Basis of presentation

The accompanying consolidated financial statements include those of the Company and its subsidiary, Voyager Securities Corporation, after elimination of all intercompany accounts and transactions. The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”).

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.

Fair Value of Financial Instruments

ASC Topic 820, Fair Value Measurement (“ASC 820”), establishes a fair value hierarchy for instruments measured at fair value that distinguishes between assumptions based on market data (observable inputs) and the Company’s own assumptions (unobservable inputs). Observable inputs are inputs that market participants would use in pricing the asset or liability based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the inputs that market participants would use in pricing the asset or liability, and are developed based on the best information available in the circumstances.

ASC 820 identifies fair value as the exchange price, or exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As a basis for considering market participant assumptions in fair value measurements, ASC 820 establishes a three-tier fair value hierarchy that distinguishes between the following:

●

Level 1—Quoted market prices in active markets for identical assets or liabilities.

●

Level 2—Inputs other than Level 1 inputs that are either directly or indirectly observable, such as quoted market prices, interest rates, and yield curves.

●

Level 3—Unobservable inputs developed using estimates of assumptions developed by the Company, which reflect those that a market participant would use.

To the extent that the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement.

The carrying amounts reflected in the balance sheets for cash and cash equivalents, prepaid expenses and other current assets, accounts payable and accrued expenses approximate their fair values, due to their short-term nature.

Cash and Cash Equivalents

The Company considers all highly liquid investments purchased with original maturities of 90 days or less at acquisition to be cash equivalents. Cash and cash equivalents include cash held in banks and amounts held in money market funds.

Marketable Securities

The Company classifies marketable debt securities with a remaining maturity of greater than three months when purchased 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. During 2016, the Company invested in a supplier and received common stock and warrants to purchase common stock in that entity. The common stock is considered an available-for-sale marketable equity security and is included in non-current marketable securities, and the warrants are included in non-current assets.

All available for sale debt 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 loss through a charge to the Company’s statements of operations and comprehensive loss. No other than temporary losses have been recognized.

Cash, cash equivalents, and marketable securities as of December 31, 2019 and 2018 consist of the following:


	Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses		Value
	(in thousands)
As of December 31, 2019
Money market funds included in cash and cash equivalents	$	78,303	$	—	$	—	$	78,303
Marketable securities:
U.S. Treasury notes		195,467		52		28		195,491
Equity securities		1,220		700		—		1,920
Total marketable securities	$	196,687	$	752	$	28	$	197,411
Total money market funds and marketable securities	$	274,990	$	752	$	28	$	275,714
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 December 31, 2019 and 2018 have a contractual maturity of one year or less.

Restricted Cash

At December 31, 2019 and 2018, the Company maintained restricted cash totaling approximately $0.7 million held in the form of money market accounts as collateral for the Company’s facility lease obligation. The balance is included within deposits in other non-current assets in the accompanying consolidated balance sheets. The following table provides a reconciliation of cash, cash equivalents, and restricted cash within the consolidated balance sheets that sum to the total of the same such amounts shown in the statements of cash flows:


	As of December 31,
	2019		2018		2017
	(in thousands)
Cash and cash equivalents	$	86,042	$	46,859	$	31,530
Restricted cash included in deposits and other noncurrent assets		735		735		735
Total cash, cash equivalents, and restricted cash	$	86,777	$	47,594	$	32,265

Property and Equipment

Property and equipment consists of laboratory equipment, furniture and office equipment, and leasehold improvements and is stated at cost, less accumulated depreciation. Maintenance and repairs that do not improve or extend the lives of the respective assets are expensed to operations as incurred; while costs of major additions and betterments are capitalized. Depreciation is calculated over the estimated useful lives of the assets using the straight-line method.

Impairment of Long-Lived Assets

The Company evaluates long-lived assets for potential impairment when events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Recoverability is measured by comparing the book values of the assets to the expected future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the book values of the assets exceed their fair value. The Company has not recognized any impairment losses from inception through December 31, 2019.

Revenue Recognition

As of December 31, 2019, all of the Company’s revenue has been generated from its collaboration agreements with Sanofi Genzyme, AbbVie, and Neurocrine.

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 the Company’s arrangements 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 milestone revenue 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.

Research and Development

Research and development costs are charged to expense as incurred in performing research and development activities. The costs include employee compensation costs, external research, consultant costs, sponsored research, in-kind services provided under its collaboration agreement with Sanofi Genzyme (“Sanofi Genzyme Collaboration Agreement”), license fees, process development and facilities costs. Facilities costs primarily include the allocation of rent, utilities and depreciation.

Leases

Under ASC 842, which was adopted January 1, 2019, the Company determines if an arrangement is or contains a lease at inception. For leases with a term of 12 months or less, the Company does not recognize a right-of-use asset or lease liability. The Company's operating leases are recognized on its consolidated balance sheet as other long-term assets, other current liabilities, and other long-term liabilities. The Company does not have any finance leases.

Right-of-use 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 right-of-use assets and liabilities are recognized at the lease commencement date based on the present value of lease payments over the lease term. As the Company’s leases typically do not provide an implicit rate, the Company uses an estimate of its incremental borrowing rate based on the information available at the lease commencement date in determining the present value of lease payments. Operating lease right-of-use assets also include the effect of any lease payments made and excludes lease incentives. The lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. Lease expense is recognized on a straight-line basis over the lease term.

The Company has lease agreements with lease and non-lease components, which are generally accounted for separately. Non-lease components as it pertains to the Company's leased premises generally refer to common area maintenance charges related to the premises.

Under prior guidance ASC 840, rent expense and lease incentives from operating leases were recognized on a straight-line basis over the lease term. The difference between rent expenses recognized and rental payments was recorded as deferred rent in the accompanying consolidated balance sheets.

Research Contract Costs and Accruals

The Company has entered into various research and development contracts with research institutions and other companies. These agreements are generally cancelable. The Company records accruals for estimated ongoing research costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates may be made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs.

Patent Costs

The Company expenses patent application and related legal costs as incurred and classifies such costs as general and administrative expenses in the accompanying statements of operations.

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, directors,

and other service providers, referred to as non-employees, including grants of restricted stock units and stock options, to be recognized as expense in the consolidated 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 to determine the fair value of restricted stock awards and restricted stock units.

The Black-Scholes option pricing model requires inputs based on certain subjective assumptions, including (i) the expected stock price volatility, (ii) the calculation of expected term of the award, (iii) the risk-free interest rate and (iv) 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, adjusted for actual forfeitures of unvested awards as they occur.

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 when the achievement of a performance condition is probable based on the expected satisfaction of the performance conditions as of the reporting date.

Income Taxes

Income taxes are recorded in accordance with ASC Topic 740, Income Taxes (“ASC 740”), which provides for deferred taxes using an asset and liability approach. Under this method, deferred tax assets and liabilities are determined based on the difference between the financial reporting and the tax reporting basis of assets and liabilities and are measured using the enacted tax rates and laws that are expected to be in effect when the differences are expected to reverse. The Company provides a valuation allowance against net deferred tax assets unless, based upon the weight of available evidence, it is more likely than not that the deferred tax assets will be realized.

The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit will more likely than not be realized. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances. As of December 31, 2019, the Company does not have any significant uncertain tax positions.

Comprehensive Loss

Comprehensive loss is comprised of net loss and other comprehensive income or loss. Other comprehensive income or loss consists of unrealized gains or losses on marketable securities.

Net Loss Per Share

Basic net loss per share is calculated by dividing the net loss by the weighted-average number of shares of common stock outstanding during the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss by the weighted-average number of shares of common stock and potentially dilutive securities outstanding for the period determined using the treasury-stock and if-converted methods.

For purposes of the diluted net loss per share, unvested restricted common stock and outstanding stock options are considered to be potentially dilutive securities, but are excluded from the calculation of diluted net loss per share because their effect would be anti-dilutive and therefore, basic and diluted net loss per share were the same for all periods presented.

The following table sets forth the outstanding potentially dilutive securities that have been excluded in the calculation of diluted net loss per share because to do so would be anti-dilutive:


	As of December 31,
	2019	2018	2017
Unvested restricted common stock awards	176,471	235,294	557,979
Unvested restricted common stock units	455,404	—	—
Outstanding stock options	5,317,326	4,225,152	3,143,566
Total	5,949,201	4,460,446	3,701,545

Concentrations of Credit Risk and Off-Balance Sheet Risk

The Company has no financial instruments with off-balance sheet risk such as foreign exchange contracts, option contracts or other foreign currency hedging arrangements. Financial instruments that potentially subject the Company to a concentration of credit risk are cash and cash equivalents. The Company’s cash is held in accounts at financial institutions that may exceed federally insured limits. The Company has not experienced any credit losses in such accounts and does not believe it is exposed to any significant credit risk on these funds.

Concentration of Suppliers

The Company is dependent on third-party manufacturers to supply certain products for research and development activities in its programs. In particular, the Company relies on a sole manufacturer to supply it with specific vectors related to the Company’s research and development programs.

Segment Information

Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker in deciding how to allocate resources and assess performance. The Company and the Company’s chief operating decision maker, the Company’s Chief Executive Officer, views the Company’s operations and manages its business as a single operating segment, which is the business of developing and commercializing gene therapies.

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 (“ROU”) 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 ROU 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.

In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (“ASU 2014-09”), which supersedes the revenue recognition requirements in ASC 605, Revenue Recognition (“ASC 605”), and most industry-specific guidance. The new standard requires that an entity recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The update also requires additional disclosure about the nature, amount, timing, and uncertainty of revenue and cash flows arising from customer contracts, including significant judgments and changes in judgments and assets recognized from costs incurred to obtain or fulfill a contract. Thereafter, a series of clarifying ASUs, narrow scope improvements and practical expedients were issued. This collective guidance resulted in the new revenue standard, ASC 606.

The Company adopted the new standard effective January 1, 2018 using the modified retrospective approach. The Company had one open contract, relating to the Sanofi Genzyme Collaboration, on the adoption date and has assessed it under the new revenue standard. The adoption of ASC 606 resulted in the changes to (i) the allocation of arrangement consideration, including the determination of estimated selling price and the allocation of variable consideration to specific performance obligations and (ii) the application of proportional performance as a measure of progress on service-related deliverables.

The Company has accounted for the impact of adopting ASC 606 as a cumulative catch-up under the modified retrospective approach, which is represented as an increase of $20.0 million to deferred revenue with an offset to accumulated deficit, effective January 1, 2018. The following financial statement line items have been shown to reflect comparative balances under ASC 606 and ASC 605 for the year ended December 31, 2018, for both of the Sanofi Genzyme Collaboration and AbbVie Tau Collaboration, collectively.

Consolidated Statements of Operations and Comprehensive Loss


	Year ended December 31, 2018
	Under ASC 606		Under ASC 605		Effect of change
	(in thousands, except per share data)
Collaboration revenue	$	7,619	$	11,095	$	(3,476)
Loss before income taxes		(88,468)		(84,992)		(3,476)
Net loss		(88,288)		(84,812)		(3,476)
Net loss per share, basic and diluted		(2.75)		(2.64)		(0.11)

Consolidated Statements of Cash Flows


	Year ended December 31, 2018
	Under ASC 606		Under ASC 605		Effect of change
	(in thousands)
Net loss	$	(88,288)	$	(84,812)	$	(3,476)
Adjustments to reconcile net loss to net cash used in operating activities:
Deferred revenue		61,380		57,904		3,476

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, 2022, 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 statement.

Fair value measurements

12 Months Ended

Dec. 31, 2019

Fair value measurements

Fair value measurements

3. Fair value measurements

Assets and liabilities measured at fair value on a recurring basis as of December 31, 2019 and 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)
	(in thousands)
December 31, 2019
Money market funds included in cash and cash equivalents	$	78,303	$	78,303	$	—	$	—
Marketable securities:
U.S. Treasury notes		195,491		195,491		—		—
Equity securities		1,920		1,920		—		—
Total marketable securities	$	197,411	$	197,411	$	—	$	—
Warrants to purchase equity securities		554		—		554		—
Total	$	276,268	$	275,714	$	554	$	—
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. Treasuries 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 (i) the expected stock price volatility, (ii) the calculation of expected term of the awards, (iii) the risk-free interest rate, and (iv) expected dividends. The assumptions utilized to value the warrants to purchase equity securities as of December 31, 2019, 2018, and 2017 are as follows:


	As of December 31,
	2019		2018		2017
Risk-free interest rate	1.6	%	2.5	%	2.0	%
Expected dividend yield	—	%	—	%	—	%
Expected term (in years)	1.7		2.7		3.7
Expected volatility	71.6	%	112.7	%	103.5	%

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

Commitments and contingencies

12 Months Ended

Dec. 31, 2019

Commitments and contingencies

Commitments and contingencies

9. Commitments and contingencies

Significant Agreements

Sanofi Genzyme Collaboration Agreement

Summary of Agreement

In February 2015, the Company entered into the Sanofi Genzyme Collaboration Agreement which included a non-refundable upfront payment of $65.0 million. In addition, contemporaneous 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 (NBIb-1817) for Parkinson’s disease (the “VY-AADC Program”), VY-FXN01 for Friedreich’s ataxia (the “FA Program”), a future program to be designated by Sanofi Genzyme (the “Future Program), and VY-HTT01 for Huntington’s disease (the “Huntington’s Program”), with an incremental option to co-commercialize VY-HTT01 in the United States and (ii) worldwide rights to VY-SMN101 (the “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.

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 is entitled to receive from a patient advocacy group, collectively Sanofi Genzyme “in-kind” and other funding.

Termination of Agreement

On June 14, 2019 (the “Termination Date”), 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, the FA Program and the 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 FA Program. The ex-U.S. rights to the FA Program have been, in turn, transferred from the Company to Neurocrine Biosciences pursuant to the collaboration and option agreement with Neurocrine Biosciences. 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 up to two 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 FA 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 made a $10.0 million upfront payment to Sanofi Genzyme and has agreed to make a $10.0 million milestone payment to Sanofi Genzyme 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 (a) the filing of an IND application for a Post-Termination HD Product or (b) 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 FA Program (collectively, “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 effective date of the Sanofi Genzyme Termination Agreement, the Company waived its right to approximately $0.4 million in unused in-kind services, the Company has relinquished its rights to the Spinal Muscular Atrophy Program, 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 (“Sanofi Licensed Products”) of up to an aggregate of $15.0 million per Sanofi 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 Sanofi Licensed Products for such specified indication surpass a specified amount, and low-to-mid single-digit tiered royalty payments on worldwide net sales of Sanofi Licensed Products, on a Sanofi Licensed Product-by-Sanofi Licensed Product basis.

Accounting Analysis

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 FA 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. The Company is currently engaged in the ongoing conduct and review of preclinical studies for its Huntington’s disease program, VY-HTT01, and expects to provide an update on the program in the second quarter of 2020, including plans to file an investigational new drug, or IND, application. 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 2020. 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 for as a reduction of the transaction price.

During the year ended December 31, 2019, the Company recognized $0.8 million of revenue related to in-kind services performed by Sanofi Genzyme under the collaboration. During the year ended December 31, 2019, the Company recognized $31.8 million of revenue related to research and development services, committee obligations performed, and the subsequent termination of the Sanofi Genzyme Collaboration. During the year ended December 31, 2018, the Company recognized $0.7 million of revenue related to research and development services and committee obligations performed under the Sanofi Genzyme Collaboration. During the year ended December 31, 2017, the Company recognized $10.1 million of revenue related to research and development services and committee obligations performed under the Sanofi Genzyme Collaboration. As of December 31, 2019, $10.0 million remains in short term deferred revenue in the accompanying consolidated balance sheet.

Costs incurred relating to the programs that Sanofi Genzyme had the option to license under the Sanofi Genzyme Collaboration Agreement consisted of internal and external research and development costs, which primarily included: salaries and benefits, lab supplies and preclinical research studies. These costs were included in research and development expenses in the Company’s consolidated statements of operations during the years ended December 31, 2019, 2018, and 2017.

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 to the Company 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 IND 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 Tau 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 (collectively, the “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 Tau 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 contract 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 years ended December 31, 2019 and 2018, the Company recognized $11.3 million and $6.9 million of revenue, respectively, associated with the AbbVie Tau Collaboration related to the Research Services performed during the period. As of December 31, 2019, there is $50.8 million of deferred revenue related to the AbbVie Tau Collaboration Agreement, which is classified as either current or noncurrent in the accompanying 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 consolidated statements of operations during the years ended December 31, 2019 and 2018.

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 to the Company 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 (the “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 contract 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 year ended December 31, 2019, the Company recognized $1.3 million of revenue associated with the AbbVie Alpha-Synuclein Collaboration related to the ASN Research Services performed during the period then ended. As of December 31, 2019, there was $63.7 million of deferred revenue related to the AbbVie Alpha-Synuclein Collaboration Agreement, which is classified as either current or non-current in the accompanying 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 consolidated statements of operations during the year ended December 31, 2019.

Neurocrine Collaboration Agreement

Summary of Agreement

In March 2019, the Company entered into 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 VY-AADC Program, (ii) the FA Program (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 FA Program. The Company’s ex-U.S. rights to the FA Program were subsequently transferred to Neurocrine under the terms of the Neurocrine Collaboration Agreement. To facilitate the transfer of the ex-U.S. rights to the FA Program to Neurocrine, the Company and Neurocrine executed an amendment to the Neurocrine Collaboration Agreement (the “June 2019 Modification”), and Neurocrine 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 VY-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 occurrence of a specified event for such Neurocrine Program (a “Transition Event”), 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 Transition Event for each Neurocrine Program, 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 VY-AADC Program, the Company’s receipt of topline data for the RESTORE-1 Phase 2 clinical trial for VY-AADC (NBIb-1817); (ii) with respect to the FA Program, the Company’s receipt of topline data for the initial Phase 1 clinical trial for an FA 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 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 VY-AADC Program, the Company’s receipt of topline data for the ongoing RESTORE-1 Phase 2 clinical trial for VY-AADC (NBIb-1817) and (ii) with respect to the FA Program, the receipt of topline data for the initial Phase 1 clinical trial for an FA 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 VY-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 biologics license application (“BLA”) from the FDA, to pay a $35.0 million rate-shifting fee to the Company to change the allocation for the VY-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 (the “Targets”) from which Neurocrine has the right to nominate Targets for the two Discovery Programs. The Targets nominated 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 VY-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 milestone payments 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) ten 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 (a) 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 (b) 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 and estimated the expected 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. The Company considers this estimate at each reporting date and updates the estimate based on information available. During the fourth quarter of 2019, the Company changed the estimate of the expected reimbursement to $365.8 million based on current expectations. 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 data, 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 expected cost reimbursement was as follows at December 31, 2019:


Performance Obligation	Amount
	(in thousands)
Variable Consideration
VY-AADC Program	$	111,098
FA Program		112,417
Discovery Program 1		71,206
Discovery Program 2		71,081
Total	$	365,802

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
VY-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 year ended December 31, 2019, the Company recognized $60.0 million of revenue associated with its collaboration with Neurocrine related to research and development services performed during the period and the corresponding cost reimbursement receivable. As of December 31, 2019, there was $70.0 million of deferred revenue related to the Neurocrine Collaboration Agreement, which is classified as either current or non-current in the accompanying consolidated balance sheet based on the period the services are expected to be delivered. Additionally, as of December 31, 2019, there was $18.5 million of collaboration 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 consolidated statements of operations during the year ended December 31, 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.

ClearPoint Neuro, Inc. 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 “CLPT License Agreement”) with ClearPoint Neuro, Inc. (formerly known as MRI Interventions, Inc.) (“CLPT”), formerly known as MRI Interventions, Inc. CLPT is the only 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 CLPT common stock and a warrant to purchase additional shares of CLPT common stock. The Company also entered into the CLPT License Agreement, which provided for certain rights to CLPT technology and for CLPT 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 CLPT License Agreement and all prior and future commitments and obligations under such agreement became null and void.

In May 2018, the Company entered into a master services and supply agreement with CLPT (the “CLPT Supply Agreement”) which provides for CLPT 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, the Company transferred its premarket notification (510(k)) clearance for the V-TAG device to CLPT, and will work with CLPT on the manufacturing and clinical supply of the device.

As of December 31, 2019, the Company continued to hold the common stock and warrants to purchase additional shares of common stock as a non-current asset.

Other Agreements

The Company has entered into various agreements with contract research organizations and institutions to license intellectual property. In consideration for the licensed rights 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 license agreements 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 December 31, 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 30-90 days prior written notice.

Additionally, certain license agreements require the Company to reimburse the licensor for certain past and ongoing patent related expenses. During the year ended December 31, 2019, 2018, and 2017, the Company incurred $0.5 million, $0.6 million, and $0.8 million of expense, respectively, related to these reimbursable patent costs which are recorded as general and administrative expense

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 through the year ended December 31, 2017 is recorded as a non-current liability in the consolidated balance sheet.

Litigation

Stock based compensation

12 Months Ended

Dec. 31, 2019

Stock based compensation

Stock based compensation

12. 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 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 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 Plan and during 2015 the Company only granted stock options.

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 (each, a “Founder”) at an original issuance price of $0.0425 per share. Of the total restricted shares awarded to the Founders, 835,292 shares generally vest 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.

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. Management concluded that the achievement of the

performance milestone for one of the three performance-based awards had been met during 2016. Accordingly, stock-based compensation expense in the amount of $0.3 million and $1.4 million was recorded in the years ended December 31, 2018 and 2017, respectively, related to this award. In December 2019, the Company modified one of the remaining performance awards, repurchasing 58,823 shares of common stock previously issued to one of the Company’s founders. Additionally, the Company modified the award to vest solely based on time rather than on performance. The Company revalued the award at the modification date and is recognizing expense on a straight-line basis over the three-year vesting period. Stock-based compensation related to this award was de minimis in the year ended December 31, 2019. The performance-based milestone of the remaining performance-based award has not been met as of December 31, 2019.

2015 Stock Option Plan

In October 2015, the Company’s board of directors and stockholders approved the 2015 Stock Option and Incentive Plan “(2015 Stock Option Plan”), which became effective upon the completion of 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, 2019, and 2020, an additional 1,069,971, 1,070,635, 1,285,200, 1,302,830, and 1,480,621 shares of common stock, respectively, were added to the Company’s 2015 Stock Option Plan pursuant to its “evergreen” provision, for future issuance. During the year ended December 31, 2019, the Company granted options to purchase 1,365,130 shares of common stock to employees and directors under the 2015 Stock Option Plan. As of December 31, 2019, there were 1,875,078 shares available for future issuance 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”). 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 2015 ESPP became effective upon the completion of the IPO. Effective January 1, 2016, 2017, 2018, 2019, and 2020, a total of 267,492, 267,658, 321,300, 325,707, and 370,155 shares of common stock, respectively, were added to the 2015 ESPP, pursuant to its evergreen provision, for future issuance. The Company issued 70,217 shares of common stock under the 2015 ESPP in the year ended December 31, 2019.

Inducement Awards

In the year ended December 31, 2019, the Company issued 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, respectively, to two executives 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 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 loss is as follows:


	Year ended December 31,
	2019		2018		2017
	(in thousands)
Research and development	$	7,383	$	4,717	$	5,367
General and administrative		8,257		10,993		3,871
Total stock-based compensation expense	$	15,640	$	15,710	$	9,238

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


	Year ended December 31,
	2019		2018		2017
	(in thousands)
Stock options	$	13,380	$	14,956	$	5,787
Restricted stock awards and units		1,935		482		3,244
Employee stock purchase plan awards		325		272		207
Total stock-based compensation expense	$	15,640	$	15,710	$	9,238

In June 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-substantive service period of the Sah Agreement.

In August 2018, the Company entered into a consulting agreement (the “Paul Agreement”) with Dr. Steven M. Paul, M.D., the Company’s former President and Chief Executive Officer, pursuant to which Dr. Paul 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 August 2, 2018. In accordance with its terms, the Paul Agreement triggered an equity modification resulting in the recognition of $5.4 million of stock-based compensation expense related to the non-substantive service period of the Paul 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 year ended December 31, 2019 was as follows:


		Weighted
		Average
		Grant Date
		Fair Value
	Units	Per Unit
Unvested restricted stock units as of December 31, 2018	—		—
Awarded	484,514	$	12.00
Vested	—		—
Forfeited	(29,110)	$	9.47
Unvested restricted stock units as of December 31, 2019	455,404

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 year ended December 31, 2019 was $12.00 per share. The restricted stock units granted in the year ended December 31, 2019 vest in equal amounts, annually over three years. The expense related to awards granted to employees was $1.9 million for the year ended December 31, 2019.

The expense related to awards granted to employees was $0.1 million for the year ended December 31, 2018. The expense related to awards granted to employees was $0.5 million for the year ended December 31, 2017.

As of December 31, 2019, the Company had unrecognized stock-based compensation expense related to its unvested restricted stock units of $4.9 million which is expected to be recognized over the remaining weighted average vesting period of 3.0 years

Stock Options

A summary of the status of, and changes in, stock options was as follows:


		Weighted		Remaining	Aggregate
		Average		Contractual	Intrinsic
		Exercise		Life	Value
	Shares	Price		(in years)	(in thousands)
Outstanding at December 31, 2018	4,225,152	$	15.48
Granted	1,703,880	$	15.42
Exercised	(250,276)	$	10.84
Cancelled or forfeited	(361,430)	$	12.12
Outstanding at December 31, 2019	5,317,326	$	15.98	8.1	$	8,469
Exercisable at December 31, 2019	2,482	$	14.67	7.3	$	5,194
Vested and expected to vest at December 31, 2019	5,317,326	$	15.98	8.1	$	8,469

Using the Black-Scholes option pricing model, the weighted average fair value of options granted to employees and directors during the year ended December 31, 2019 was $10.22. The stock-based compensation expense related to stock option awards granted to employees and directors was $13.3 million, $14.6 million, and $5.4 million for the years ended December 31, 2019, 2018, and 2017, 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:


	Year ended December 31,
	2019		2018		2017
Risk-free interest rate	2.2	%	2.8	%	2.0	%
Expected dividend yield	—	%	—	%	—	%
Expected term (in years)	6.0		6.0		6.0
Expected volatility	74.7	%	74.4	%	73.7	%

There were no new options granted to non-employees other than members of the Company’s board of directors during the year ended December 31, 2019. The expense related to stock option awards granted to non-employees was $0.1 million, $0.3 million, and $0.4 million for the years ended December 31, 2019, 2018, and 2017, respectively.

As of December 31, 2019, the Company had unrecognized stock-based compensation expense related to its unvested stock options of $27.4 million which is expected to be recognized over the remaining weighted average vesting period of 2.6 years.

Income taxes

12 Months Ended

Dec. 31, 2019

Income taxes

Income taxes

14. Income taxes

The Company accounts for income taxes using the asset and liability method. Under the asset and liability method, deferred tax assets and liabilities are recognized for the future tax consequences attributable to temporary differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and for tax carryforwards, such as net operating losses. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in the provision for income taxes in the period that includes the enactment date. The Company records a valuation allowance to reduce the carrying amount of deferred tax assets if it is more likely than not that such asset will not be realized. The evaluation of uncertain tax positions is based on factors including, but not limited to, changes in the law, the measurement of tax positions taken or expected to be taken in tax returns, the effective settlement of matters subject to audit, new audit activity, and changes in facts or circumstances related to a tax position. The Company evaluates its tax positions on a quarterly basis.

On December 22, 2017, the U.S. federal government enacted comprehensive tax legislation with the U.S. Tax Cuts and Jobs Act (“Tax Act”) that made changes to the U.S. tax code impacting the year ended December 31, 2017 and future years. Effective January 1, 2018, the Tax Act reduced the U.S. federal corporate tax rate from 35% to 21%.

For the year ended December 31, 2017, the Tax Act required a one-time transition tax on certain unrepatriated earnings of foreign subsidiaries that is payable over eight years. At December 31, 2018, the Company does not have any foreign subsidiaries and the international aspects of the Tax Act are not applicable.

In December 2017, the SEC staff issued Staff Accounting Bulletin No. 118 (“SAB 118”), which provided guidance on accounting for the tax effects of the Tax Act. SAB 118 provided a measurement period that should not extend beyond one year from the date of the Tax Act enactment for companies to complete the accounting under Accounting Standards Codification 740—Income Taxes. In accordance with SAB 118, to the extent that a company’s accounting for certain income tax effects of the Tax Act is incomplete, but the company is able to determine a reasonable estimate, it must record a provisional estimate in its financial statements. The Company’s accounting for the Tax Act was completed in the fourth quarter of 2018 and resulted in no adjustments to the Company’s prior provisional estimates recorded in the period ended December 31, 2017.

The benefit for incomes taxes is as follows:


	Year ended December 31,
	2019		2018
	(in thousands)
Current
Federal	$	—	$	180
State		—		—
Total current		—		180

Deferred
Federal		—		—
State		—		—
Total deferred		—		—
Total tax expense	$	—	$	180

A reconciliation of the expected income tax (benefit) computed using the federal statutory income tax rate at the Company’s effective tax rate is as follows:


	Year ended December 31,
	2019			2018			2017
Income tax computed at federal statutory tax rate		21.0	%		21.0	%		34.0	%
General business credit carryovers		9.4	%		3.1	%		5.0	%
State taxes, net of federal benefit		8.0	%		6.3	%		6.1	%
Deferred rate change		—	%		—	%		(21.8)	%
Non-deductible expenses		(2.2)	%		(2.1)	%		(4.1)	%
Change in valuation allowance		(36.2)	%		(28.1)	%		(19.2)	%
Total		—	%		0.2	%		—	%

The Company has incurred net operating losses (“NOLs”) since June 2013. At December 31, 2019, the Company had federal and state net operating loss carryforwards of $182.4 million and $180.4 million, respectively. During 2019, the company generated federal and state NOLs carryforwards of $19.1 million and $16.1million, respectively. The federal pre-2017 NOL will begin to expire in 2033. The post-2017 NOL are limited to 80% of taxable income and with an indefinite carryforward period. The state NOL carryforwards will begin to expire in 2033. As of December 31, 2019, the Company also had federal and state research and development tax credit carryforwards of $13.4 million and $4.3 million, respectively, which expire beginning in 2028. As of December 31, 2019, the Company had state investment credits of $0.6 million, which expire beginning in 2019.

Under the provisions of the Internal Revenue Code, certain substantial changes in the Company’s ownership may result in a limitation on the amount of NOL carryforwards and research and development credit carryforwards that may be utilized annually to offset future taxable income and taxes payable. In general, an ownership change, as defined by Section 382, results from transactions that increase the ownership of 5% stockholders or public groups in the stock of a corporation by more than 50 percent in the aggregate over a three-year period. During 2016, the Company completed a study through June 30, 2016, to determine whether any ownership change had occurred since the Company’s formation and determined that its transactions had resulted in three ownership changes, as defined by Section 382. An updated study was completed through May 3, 2019 and there were no additional ownership changes. There could be additional ownership changes in the future that could further limit the amount of NOLs and tax credit carryforwards that the Company can utilize.

The significant components of the Company’s deferred tax assets and (liabilities) as of December 31, 2019 and 2018 are as follows:


	Year ended December 31,
	2019		2018
	(in thousands)
Deferred tax assets:
Net operating loss carryforwards	$	49,713	$	44,556
Tax credit carryforwards		17,297		12,021
Deferred rent		—		1,560
Lease liability		9,335		—
Deferred revenue		16,805		13,926
Non-deductible accruals and reserves		1,502		1,105
Intangibles		776		930
Stock compensation		5,157		2,802
Total deferred tax assets		100,585		76,900
Less valuation allowance		(90,920)		(75,213)
Net deferred tax assets		9,665		1,687
Deferred tax liabilities
Unrealized gain on available-for-sale securities		(8)		—
Depreciation and amortization		(1,878)		(1,687)
Right of use asset		(7,779)		—
Net deferred taxes	$	—	$	—

As required by ASC 740, management has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets, which principally comprise NOL carryforwards, research and development credit carryforwards, and collaboration revenue that has been recognized as taxable but remains deferred for book reporting purposes at year end. . Management has determined that it is more likely than not that the Company will not recognize the benefits of its federal and state deferred tax assets, and as a result, a valuation allowance of $90.9 million and $75.2 million has been established at December 31, 2019 and 2018, respectively. The change in valuation allowance was $15.7 million for the year ended December 31, 2019, primarily due to additional operating losses incurred by the Company for the year ended December 31, 2019 and current year increase in stock compensation deferred tax asset. The primary reason for the difference between the income tax expense recorded by the Company and the amount of income tax expense at statutory income tax rates was the change in the valuation allowance.

At December 31, 2019 and 2018, the Company had no unrecognized tax benefits. The Company has not as yet conducted a study of its research and development credit carryforwards. This study may result in an adjustment to the Company’s research and development credit carryforwards; however, until a study is completed, and any adjustment is known, no amounts are being presented as an uncertain tax position. A full valuation allowance has been provided against the Company’s research and development credits, and if an adjustment is required, this adjustment would be offset by an adjustment to the valuation allowance. Thus, there would be no impact to the balance sheets or statements of operations if an adjustment were required.

Interest and penalty charges, if any, related to unrecognized tax benefits would be classified as income tax expense in the accompanying statements of operations. As of December 31, 2019 and 2018, the Company has no accrued interest related to uncertain tax positions. Since the Company is in a loss carryforward position, it is generally subject to examination by the U.S. federal, state, and local income tax authorities for all tax years in which a loss carryforward is available.

Summary of significant accounting policies (Policies)

12 Months Ended

Dec. 31, 2019

Summary of significant accounting policies

Basis of Presentation

Basis of presentation

Use of estimates

Use of Estimates

Fair Value of Financial Instruments

●

Level 1—Quoted market prices in active markets for identical assets or liabilities.

●

Level 2—Inputs other than Level 1 inputs that are either directly or indirectly observable, such as quoted market prices, interest rates, and yield curves.

●

Level 3—Unobservable inputs developed using estimates of assumptions developed by the Company, which reflect those that a market participant would use.

Cash and Cash Equivalents

Marketable Securities

Cash, cash equivalents, and marketable securities as of December 31, 2019 and 2018 consist of the following:


	Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses		Value
	(in thousands)
As of December 31, 2019
Money market funds included in cash and cash equivalents	$	78,303	$	—	$	—	$	78,303
Marketable securities:
U.S. Treasury notes		195,467		52		28		195,491
Equity securities		1,220		700		—		1,920
Total marketable securities	$	196,687	$	752	$	28	$	197,411
Total money market funds and marketable securities	$	274,990	$	752	$	28	$	275,714
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 December 31, 2019 and 2018 have a contractual maturity of one year or less.

Restricted Cash


	As of December 31,
	2019		2018		2017
	(in thousands)
Cash and cash equivalents	$	86,042	$	46,859	$	31,530
Restricted cash included in deposits and other noncurrent assets		735		735		735
Total cash, cash equivalents, and restricted cash	$	86,777	$	47,594	$	32,265

Property and Equipment

Impairment of Long-Lived Assets

Revenue Recognition

As of December 31, 2019, all of the Company’s revenue has been generated from its collaboration agreements with Sanofi Genzyme, AbbVie, and Neurocrine.

Research and Development

Leases

Research Contract Costs and Accruals

Patent Costs

The Company expenses patent application and related legal costs as incurred and classifies such costs as general and administrative expenses in the accompanying statements of operations.

Stock-based Compensation Expense

Stock-Based Compensation Expense

Income Taxes

Comprehensive Loss

Comprehensive loss is comprised of net loss and other comprehensive income or loss. Other comprehensive income or loss consists of unrealized gains or losses on marketable securities.

Net Loss Per Share

The following table sets forth the outstanding potentially dilutive securities that have been excluded in the calculation of diluted net loss per share because to do so would be anti-dilutive:


	As of December 31,
	2019	2018	2017
Unvested restricted common stock awards	176,471	235,294	557,979
Unvested restricted common stock units	455,404	—	—
Outstanding stock options	5,317,326	4,225,152	3,143,566
Total	5,949,201	4,460,446	3,701,545

Concentrations of Credit Risk and Off Balance Sheet Risk & Concentration of Suppliers

Concentrations of Credit Risk and Off-Balance Sheet Risk

Concentration of Suppliers

Segment Information

Recent Accounting Pronouncements

Recently Adopted Accounting Pronouncements

Consolidated Statements of Operations and Comprehensive Loss


	Year ended December 31, 2018
	Under ASC 606		Under ASC 605		Effect of change
	(in thousands, except per share data)
Collaboration revenue	$	7,619	$	11,095	$	(3,476)
Loss before income taxes		(88,468)		(84,992)		(3,476)
Net loss		(88,288)		(84,812)		(3,476)
Net loss per share, basic and diluted		(2.75)		(2.64)		(0.11)

Consolidated Statements of Cash Flows


	Year ended December 31, 2018
	Under ASC 606		Under ASC 605		Effect of change
	(in thousands)
Net loss	$	(88,288)	$	(84,812)	$	(3,476)
Adjustments to reconcile net loss to net cash used in operating activities:
Deferred revenue		61,380		57,904		3,476

Recent Accounting Pronouncements

Summary of significant accounting policies (Tables)

12 Months Ended

Dec. 31, 2019

New Accounting Pronouncements or Change in Accounting Principle [Line Items]

Cash, cash equivalents and marketable securities

Cash, cash equivalents, and marketable securities as of December 31, 2019 and 2018 consist of the following:


	Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses		Value
	(in thousands)
As of December 31, 2019
Money market funds included in cash and cash equivalents	$	78,303	$	—	$	—	$	78,303
Marketable securities:
U.S. Treasury notes		195,467		52		28		195,491
Equity securities		1,220		700		—		1,920
Total marketable securities	$	196,687	$	752	$	28	$	197,411
Total money market funds and marketable securities	$	274,990	$	752	$	28	$	275,714
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

Reconciliation of cash, cash equivalents, and restricted cash


	As of December 31,
	2019		2018		2017
	(in thousands)
Cash and cash equivalents	$	86,042	$	46,859	$	31,530
Restricted cash included in deposits and other noncurrent assets		735		735		735
Total cash, cash equivalents, and restricted cash	$	86,777	$	47,594	$	32,265

Outstanding potentially dilutive securities excluded in the calculation of diluted net loss per share

The following table sets forth the outstanding potentially dilutive securities that have been excluded in the calculation of diluted net loss per share because to do so would be anti-dilutive:


	As of December 31,
	2019	2018	2017
Unvested restricted common stock awards	176,471	235,294	557,979
Unvested restricted common stock units	455,404	—	—
Outstanding stock options	5,317,326	4,225,152	3,143,566
Total	5,949,201	4,460,446	3,701,545

ASU 2014-09

New Accounting Pronouncements or Change in Accounting Principle [Line Items]

Schedule of impact of adoption of financial statement line items shows comparative balances under ASC 606 and ASC 605

Consolidated Statements of Operations and Comprehensive Loss


	Year ended December 31, 2018
	Under ASC 606		Under ASC 605		Effect of change
	(in thousands, except per share data)
Collaboration revenue	$	7,619	$	11,095	$	(3,476)
Loss before income taxes		(88,468)		(84,992)		(3,476)
Net loss		(88,288)		(84,812)		(3,476)
Net loss per share, basic and diluted		(2.75)		(2.64)		(0.11)

Consolidated Statements of Cash Flows


	Year ended December 31, 2018
	Under ASC 606		Under ASC 605		Effect of change
	(in thousands)
Net loss	$	(88,288)	$	(84,812)	$	(3,476)
Adjustments to reconcile net loss to net cash used in operating activities:
Deferred revenue		61,380		57,904		3,476

Fair value measurements (Tables)

12 Months Ended

Dec. 31, 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 December 31, 2019 and 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)
	(in thousands)
December 31, 2019
Money market funds included in cash and cash equivalents	$	78,303	$	78,303	$	—	$	—
Marketable securities:
U.S. Treasury notes		195,491		195,491		—		—
Equity securities		1,920		1,920		—		—
Total marketable securities	$	197,411	$	197,411	$	—	$	—
Warrants to purchase equity securities		554		—		554		—
Total	$	276,268	$	275,714	$	554	$	—
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


	As of December 31,
	2019		2018		2017
Risk-free interest rate	1.6	%	2.5	%	2.0	%
Expected dividend yield	—	%	—	%	—	%
Expected term (in years)	1.7		2.7		3.7
Expected volatility	71.6	%	112.7	%	103.5	%

Stock based compensation (Tables)

12 Months Ended

Dec. 31, 2019

Stock based compensation

Compensation cost recognized for all stock-based compensation awards


	Year ended December 31,
	2019		2018		2017
	(in thousands)
Research and development	$	7,383	$	4,717	$	5,367
General and administrative		8,257		10,993		3,871
Total stock-based compensation expense	$	15,640	$	15,710	$	9,238

Summary of stock-based compensation expense by classification


	Year ended December 31,
	2019		2018		2017
	(in thousands)
Stock options	$	13,380	$	14,956	$	5,787
Restricted stock awards and units		1,935		482		3,244
Employee stock purchase plan awards		325		272		207
Total stock-based compensation expense	$	15,640	$	15,710	$	9,238

Summary of status and changes in unvested restricted stock


		Weighted
		Average
		Grant Date
		Fair Value
	Units	Per Unit
Unvested restricted stock units as of December 31, 2018	—		—
Awarded	484,514	$	12.00
Vested	—		—
Forfeited	(29,110)	$	9.47
Unvested restricted stock units as of December 31, 2019	455,404

Summary of status and changes in stock options


		Weighted		Remaining	Aggregate
		Average		Contractual	Intrinsic
		Exercise		Life	Value
	Shares	Price		(in years)	(in thousands)
Outstanding at December 31, 2018	4,225,152	$	15.48
Granted	1,703,880	$	15.42
Exercised	(250,276)	$	10.84
Cancelled or forfeited	(361,430)	$	12.12
Outstanding at December 31, 2019	5,317,326	$	15.98	8.1	$	8,469
Exercisable at December 31, 2019	2,482	$	14.67	7.3	$	5,194
Vested and expected to vest at December 31, 2019	5,317,326	$	15.98	8.1	$	8,469

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:


	Year ended December 31,
	2019		2018		2017
Risk-free interest rate	2.2	%	2.8	%	2.0	%
Expected dividend yield	—	%	—	%	—	%
Expected term (in years)	6.0		6.0		6.0
Expected volatility	74.7	%	74.4	%	73.7	%

Income taxes (Tables)

12 Months Ended

Dec. 31, 2019

Income taxes

Schedule of components of income expense (benefit)


	Year ended December 31,
	2019		2018
	(in thousands)
Current
Federal	$	—	$	180
State		—		—
Total current		—		180

Deferred
Federal		—		—
State		—		—
Total deferred		—		—
Total tax expense	$	—	$	180

A reconciliation of the expected income tax (benefit) computed using the federal statutory income tax rate at the Company’s effective tax rate is as follows:


	Year ended December 31,
	2019			2018			2017
Income tax computed at federal statutory tax rate		21.0	%		21.0	%		34.0	%
General business credit carryovers		9.4	%		3.1	%		5.0	%
State taxes, net of federal benefit		8.0	%		6.3	%		6.1	%
Deferred rate change		—	%		—	%		(21.8)	%
Non-deductible expenses		(2.2)	%		(2.1)	%		(4.1)	%
Change in valuation allowance		(36.2)	%		(28.1)	%		(19.2)	%
Total		—	%		0.2	%		—	%

Schedule of reconciliation of the expected income tax (benefit) computed using the federal statutory income tax rate to the effective income tax rate

Schedule of principal components of the Company's deferred tax assets and liabilities


	Year ended December 31,
	2019		2018
	(in thousands)
Deferred tax assets:
Net operating loss carryforwards	$	49,713	$	44,556
Tax credit carryforwards		17,297		12,021
Deferred rent		—		1,560
Lease liability		9,335		—
Deferred revenue		16,805		13,926
Non-deductible accruals and reserves		1,502		1,105
Intangibles		776		930
Stock compensation		5,157		2,802
Total deferred tax assets		100,585		76,900
Less valuation allowance		(90,920)		(75,213)
Net deferred tax assets		9,665		1,687
Deferred tax liabilities
Unrealized gain on available-for-sale securities		(8)		—
Depreciation and amortization		(1,878)		(1,687)
Right of use asset		(7,779)		—
Net deferred taxes	$	—	$	—

Summary of significant accounting policies - Recently adopted accounting pronouncements (Details) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019 USD ($) $ / shares	Sep. 30, 2019 USD ($) $ / shares	Jun. 30, 2019 USD ($) $ / shares	Mar. 31, 2019 USD ($) $ / shares	Dec. 31, 2018 USD ($) $ / shares	Sep. 30, 2018 USD ($) $ / shares	Jun. 30, 2018 USD ($) $ / shares	Mar. 31, 2018 USD ($) $ / shares	Dec. 31, 2019 USD ($) item $ / shares	Dec. 31, 2018 USD ($) $ / shares	Dec. 31, 2017 USD ($) $ / shares
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of open contracts \| item									1
Lease, Practical Expedients, Package [true false]									true
Operating lease, right-of-use asset	$ 28,472								$ 28,472
Operating lease liability	34,168								34,168
Increase to deferred revenue with an offset to accumulated deficit									20,000
Consolidated Statements of Operations and Comprehensive Loss
Collaboration revenue	32,674	$ 20,433	$ 46,087	$ 5,197	$ 2,008	$ 2,094	$ 2,575	$ 942	104,391	$ 7,619	$ 10,135
Loss before income taxes									(43,597)	(88,468)	(70,698)
Net loss	$ (12,574)	$ (15,006)	$ 11,153	$ (27,170)	$ (22,532)	$ (20,289)	$ (25,541)	$ (19,926)	$ (43,597)	$ (88,288)	$ (70,698)
Net loss per share, basic and diluted \| $ / shares	$ (0.34)	$ (0.41)	$ 0.30	$ (0.81)	$ (0.70)	$ (0.63)	$ (0.80)	$ (0.63)	$ (1.21)	$ (2.75)	$ (2.64)
Consolidated Statement of Cash Flows
Net loss									$ (43,597)	$ (88,288)	$ (70,698)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Deferred revenue									80,831	61,380	$ (10,135)
ASU 2016-02 \| Restatement Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, right-of-use asset	$ 31,000								31,000
Operating lease liability	$ 36,700								$ 36,700
ASU 2014-09 \| Under ASC 605
Consolidated Statements of Operations and Comprehensive Loss
Collaboration revenue										11,095
Loss before income taxes										(84,992)
Net loss										$ (84,812)
Net loss per share, basic and diluted \| $ / shares										$ (2.64)
Consolidated Statement of Cash Flows
Net loss										$ (84,812)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Deferred revenue										57,904
ASU 2014-09 \| Effect of change
Consolidated Statements of Operations and Comprehensive Loss
Collaboration revenue										(3,476)
Loss before income taxes										(3,476)
Net loss										$ (3,476)
Net loss per share, basic and diluted \| $ / shares										$ (0.11)
Consolidated Statement of Cash Flows
Net loss										$ (3,476)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Deferred revenue										$ 3,476

Lease obligation (Details) $ in Thousands	1 Months Ended	12 Months Ended
Lease obligation (Details) $ in Thousands	Apr. 30, 2014 item	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Lessee, Operating Lease, Existence of Option to Extend [true false]		true
Rent expense		$ 5,700	$ 4,000	$ 2,900
Restricted cash included in deposits and other noncurrent assets		$ 735	$ 735	$ 735
Weighted average remaining lease term		6 years 10 months 24 days
Weighted average incremental borrowing rate		8.5
Total minimum lease payments
2020		$ 5,960
2021		6,138
2022		6,323
2023		6,512
2024		6,707
2025+		14,190
Total future minimum lease payments		45,830
Less: imputed interest		(11,662)
Total lease liability		$ 34,168
Operating Lease, Liability, Statement of Financial Position [Extensible List]		us-gaap:OtherLiabilitiesCurrent us-gaap:OtherLiabilitiesNoncurrent
Current lease liabilities		$ 3,193
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]		Other Liabilities, Current
Non-current lease liabilities		$ 30,975
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]		Other Liabilities, Noncurrent
75 Sidney Street
Number of renewal options \| item	2
Term of each renewal option	5 years
Leasehold improvements		$ 1,300
Entitled leasehold improvements		100
64 Sidney Street
Leasehold improvements		$ 3,500

Commitments and contingencies - Neurocrine Collaboration Agreement - (Details) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended	12 Months Ended
	Jun. 30, 2019 USD ($) shares	Mar. 31, 2019 USD ($) item $ / shares shares	Dec. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2017 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Purchase of common stock					$ 57,994
Neurocrine \| FA Program
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage of profit or loss under co-co option		60.00%
Neurocrine Collaboration Agreement \| Parkinson's Program
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		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
Programs added later \| 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	$ 5,000	$ 50,000
Price per share \| $ / shares		$ 11.9625
Aggregate maximum milestone payments to be received from collaborative partner		$ 170,000
Estimated cost reimbursement	431,100		$ 365,800
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
Allocation of Transaction Price
Allocation of variable consideration			365,802	$ 365,802
Allocation of fixed consideration	92,400		92,382	92,382
Revenue recognized				60,000
Deferred revenue			70,000	70,000
Reimbursement costs expected to be received				18,500
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 \| Parkinson's Program
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			111,098	111,098
Allocation of fixed consideration			80,373	80,373
Neurocrine Collaboration Agreement \| Neurocrine \| FA Program
Allocation of Transaction Price
Allocation of variable consideration			112,417	112,417
Allocation of fixed consideration			6,005	6,005
Neurocrine Collaboration Agreement \| Neurocrine \| Discovery program 1
Allocation of Transaction Price
Allocation of variable consideration			71,206	71,206
Allocation of fixed consideration			3,002	3,002
Neurocrine Collaboration Agreement \| Neurocrine \| Discovery program 2
Allocation of Transaction Price
Allocation of variable consideration			71,081	71,081
Allocation of fixed consideration			$ 3,002	$ 3,002
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) $ / shares in Units, $ in Thousands						1 Months Ended			12 Months Ended
	Jan. 01, 2020 shares	Jan. 01, 2019 shares	Jan. 01, 2018 shares	Jan. 01, 2017 shares	Jan. 01, 2016 shares	Dec. 31, 2019 USD ($) $ / shares shares	Oct. 31, 2015 shares	Jan. 31, 2014 $ / shares shares	Dec. 31, 2019 USD ($) item $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($)	Dec. 31, 2016 item	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]
Shares available for future issuance (in shares)						9,043,155			9,043,155	7,397,059
Stock-based compensation \| $									$ 15,640	$ 15,710	$ 9,238
Stock options granted (in shares)									1,703,880
Exercise price \| $ / shares						$ 15.98			$ 15.98	$ 15.48
Granted (in dollars per share) \| $ / shares									$ 15.42
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]
New stock options issued									70,217
Number of shares authorized for stock-based compensation plan (in shares)	370,155	325,707	321,300	267,658	267,492		262,362
Period to purchase shares									6 months
2015 Employee Stock Purchase Plan \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of payroll deduction							1
2015 Employee Stock Purchase Plan \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of payroll deduction							10
2015 Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future issuance (in shares)						1,875,078	1,311,812		1,875,078
Percentage limit of issued and outstanding shares up to which additional shares may be issued							4.00%
Additional shares added to stock option plan	1,480,621	1,302,830	1,285,200	1,070,635	1,069,971
Outstanding stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation \| $									$ 13,380	$ 14,956	5,787
Outstanding stock options \| Inducement Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
New stock options issued									58,125
Number of executives issued awards \| item									2
Vesting period									4 years
Outstanding stock options \| Inducement Awards \| Vesting period, tranche one
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage									25.00%
Outstanding 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%
Unvested restricted common stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation \| $									$ 1,935	482	3,244
Unrecognized stock-based compensation expense \| $						$ 4,900			$ 4,900
Vesting period									3 years
Granted (in shares)									484,514
Restricted stock granted, original issued price (in dollars per share) \| $ / shares									$ 12.00
Unvested restricted common stock units \| Inducement Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period									3 years
Unvested restricted common stock units \| Inducement Awards \| Vesting period, tranche one
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage									33.00%
Unvested restricted common stock units \| Inducement Awards \| Vesting period, tranche two
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 Repurchase Program, Remaining Number of Shares Authorized to be Repurchased						58,823			58,823
Stock-based compensation \| $										300	1,400
Vesting period						3 years
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
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
Employees and directors stock options \| 2014 Stock Option and Grant Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period									4 years
Employees and directors stock options \| 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%
Employees and directors stock options \| 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
Vesting percentage									75.00%
Employees and directors stock options \| 2015 Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted (in shares)									1,365,130
Non-employees stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted (in shares)									0
Non-employees stock options \| 2014 Stock Option and Grant Plan \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period									1 year
Non-employees stock options \| 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, Employee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation \| $									$ 13,300	14,600	5,400
Share-based Payment Arrangement, Employee \| Unvested restricted common stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation \| $									1,900	100	500
Share-based Payment Arrangement, Nonemployee \| Outstanding stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation \| $									100	300	400
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation \| $									7,383	4,717	5,367
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation \| $									$ 8,257	$ 10,993	$ 3,871

Stock based compensation - Stock Options - (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding, beginning balance (in shares)	4,225,152
Granted (in shares)	1,703,880
Exercised (in shares)	(250,276)
Cancelled or forfeited (in shares)	(361,430)
Outstanding, ending balance (in shares)	5,317,326	4,225,152
Exercisable (in shares)	2,482
Vested and expected to vest (in shares)	5,317,326
Weighted Average Exercise Price
Outstanding (in dollars per share)	$ 15.48
Granted (in dollars per share)	15.42
Exercised (in dollars per share)	10.84
Cancelled or forfeited (in dollars per share)	12.12
Outstanding (in dollars per share)	15.98	$ 15.48
Exercisable (in dollars per share)	14.67
Vested and expected to vest (in dollars per share)	$ 15.98
Remaining Contractual Life
Outstanding	8 years 1 month 6 days
Exercisable	7 years 3 months 18 days
Vested and expected to vest	8 years 1 month 6 days
Aggregate Intrinsic Value
Outstanding	$ 8,469
Exercisable	5,194
Vested and expected to vest	8,469
Options disclosures
Stock-based compensation	15,640	$ 15,710	$ 9,238
Outstanding stock options
Options disclosures
Stock-based compensation	$ 13,380	14,956	5,787
Non-employees stock options
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Granted (in shares)	0
Share-based Payment Arrangement, Employee
Options disclosures
Weighted average fair value of grants (in dollars per share)	$ 10.22
Stock-based compensation	$ 13,300	14,600	5,400
Share-based Payment Arrangement, Nonemployee \| Outstanding stock options
Options disclosures
Stock-based compensation	$ 100	$ 300	$ 400

Income taxes - Deferred tax assets (liabilities) and unrecognized tax benefits (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Income taxes
Unrecognized tax benefits	$ 0	$ 0
Amounts in uncertain tax position	0
Accrued interest	0	0
Deferred tax assets:
Net operating loss carryforwards	49,713	44,556
Tax credit carryforwards	17,297	12,021
Deferred rent		1,560
Lease liability	9,335
Deferred revenue	16,805	13,926
Non-deductible accruals and reserves	1,502	1,105
Intangibles	776	930
Stock compensation	5,157	2,802
Total deferred tax assets	100,585	76,900
Less valuation allowance	(90,920)	(75,213)
Net deferred tax assets	9,665	1,687
Deferred tax liabilities
Accrued expenses	(8)
Depreciation and amortization	(1,878)	(1,687)
Right of use asset	(7,779)
Net deferred taxes	$ 0	$ 0

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2019	Dec. 31, 2018
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	36,865,116	32,364,895
Common Stock, Shares, Outstanding	36,865,116	32,364,895

Consolidated Statements of Stockholders' Equity (Parenthetical) $ in Thousands	Dec. 31, 2017 USD ($)
Consolidated Statements of Stockholders' Equity
Discounts and issuance costs	$ 4,100

Summary of significant accounting policies - Marketable Securities (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Amortized Cost
Cash and cash equivalents	$ 86,042,000	$ 46,859,000	$ 31,530,000
Marketable securities, amortized cost	196,687,000	110,171,000
Total money market funds and marketable securities	274,990,000	156,344,000
Fair Value
Marketable securities, fair value	197,411,000	109,575,000
Total money market funds and marketable securities	275,714,000	155,748,000
Unrealized Gains and Losses
Marketable securities, unrealized gains	752,000	1,000
Total money market funds and marketable securities	752,000	1,000
Marketable securities, unrealized losses	28,000	597,000
Total money market funds and marketable securities	28,000	$ 597,000
Other than temporary losses	$ 0
Maximum
Unrealized Gains and Losses
Debt securities, contractual maturity period	1 year	1 year
Money market funds
Amortized Cost
Cash and cash equivalents	$ 78,303,000	$ 46,173,000
Fair Value
Cash and cash equivalents	78,303,000	46,173,000
U.S. Treasury notes
Amortized Cost
Marketable securities, amortized cost	195,467,000	108,951,000
Fair Value
Marketable securities, fair value	195,491,000	108,947,000
Unrealized Gains and Losses
Marketable securities, unrealized gains	52,000	1,000
Marketable securities, unrealized losses	28,000	5,000
Equity securities
Amortized Cost
Marketable securities, amortized cost	1,220,000	1,220,000
Fair Value
Marketable securities, fair value	1,920,000	628,000
Unrealized Gains and Losses
Marketable securities, unrealized gains	$ 700,000
Marketable securities, unrealized losses		$ 592,000

Prepaid expenses and other current assets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Prepaid expense and other current assets
Prepaid research and development contracts	$ 1,999	$ 4,497
Other current assets	1,952	1,360
Accrued interest receivable	203	617
Prepaid insurance	476	201
Total	$ 4,630	$ 6,675

Property and equipment, net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 25,643	$ 17,878
Less: accumulated depreciation	(7,657)	(5,107)
Property and equipment, net	17,986	12,771
Depreciation expense	2,765	2,117	$ 1,595
Laboratory equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	13,748	8,843
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	7,129	7,035
Construction in progress
Property, Plant and Equipment [Line Items]
Property and equipment, gross	2,188	19
Furniture and office equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,888	1,675
Other
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 690	$ 306

Nature of business (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Nature of business
Accumulated deficit	$ (312,648)	$ (269,051)

Summary of significant accounting policies - Basis of Presentation - (Details) - shares	Dec. 31, 2019	Dec. 31, 2018
Summary of significant accounting policies
Common stock sales	36,865,116	32,364,895

Fair value measurements - Assets measured on a recurring basis - (Details) $ in Thousands	Dec. 31, 2019 USD ($) item	Dec. 31, 2018 USD ($) item	Dec. 31, 2017 USD ($) item
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	$ 86,042	$ 46,859	$ 31,530
Measurement Input, Risk-Free Interest Rate
Fair value assumptions
Warrants, measurement input \| item	0.016	0.025	0.020
Measurement Input, Expected Dividend Yield
Fair value assumptions
Warrants, measurement input	0
Measurement Input, Expected Term
Fair value assumptions
Warrants, measurement input \| item	1.7	2.7	3.7
Measurement Input, Expected Volatility
Fair value assumptions
Warrants, measurement input \| item	0.716	1.127	1.035
Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Marketable securities	$ 197,411	$ 109,575
Total assets measured at fair value	276,268	155,982
Level 1 \| Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Marketable securities	197,411	109,575
Total assets measured at fair value	275,714	155,748
Level 2 \| Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Total assets measured at fair value	554	234
U.S. Treasury notes \| Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Marketable securities	195,491	108,947
U.S. Treasury notes \| Level 1 \| Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Marketable securities	195,491	108,947
Equity securities \| Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Marketable securities	1,920	628
Equity securities \| Level 1 \| Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Marketable securities	1,920	628
Warrants \| Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Warrants to purchase equity securities	554	234
Warrants \| Level 2 \| Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Warrants to purchase equity securities	554	234
Money market funds
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	78,303	46,173
Money market funds \| Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	78,303	46,173
Money market funds \| Level 1 \| Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	$ 78,303	$ 46,173

Accrued expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Accrued expenses
Research and development costs	$ 13,248	$ 3,555
Employee compensation costs	5,733	3,780
Accrued goods and services	1,386	784
Professional services	897	1,448
Other	177	101
Patent costs	75	120
Total	$ 21,516	$ 9,788

Other liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Other current liabilities
Lease liability	$ 3,193
Total other current liabilities	3,193
Other non-current liabilities
Lease liabilities	30,975
Deferred rent		$ 5,710
Other	1,001	1,001
Total other non-current liabilities	$ 31,976	$ 6,711

Commitments and contingencies - Significant Agreements - (Details) - Sanofi Genzyme - USD ($) $ in Millions		1 Months Ended
	Jun. 14, 2019	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
Up-front fee paid on date of termination	$ 10.0
Milestone payable upon achievement	10.0
Termination Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Non-refundable upfront payment received	$ 1.0
Spinal Muscular Atrophy Program \| Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Maximum potential in-kind services to be provided by collaborative partner		$ 5.0
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

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
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) $ in Millions		1 Months Ended		12 Months Ended
	Jun. 14, 2019 USD ($)	Feb. 28, 2018 USD ($) item	Feb. 28, 2015 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Sanofi Genzyme \| Huntington's Program
Income Statement Related Disclosures [Abstract]
Deferred revenue				$ 10.0
Sanofi Genzyme \| Collaborative Arrangement
Allocable arrangement consideration
Non-refundable upfront payment received			$ 65.0
Additional consideration, premium over fair value on temporary equity issued			$ 5.0
Income Statement Related Disclosures [Abstract]
Revenue recognized	$ 28.7			0.8	$ 0.7	$ 10.1
Deferred revenue	48.7
Up-front fee paid on date of termination	10.0
Milestone payable upon achievement	10.0
Total payable amount	20.0
Sanofi Genzyme \| Collaborative Arrangement \| Research and Development Services
Income Statement Related Disclosures [Abstract]
Revenue recognized				31.8
Sanofi Genzyme \| Termination Agreement
Allocable arrangement consideration
Non-refundable upfront payment received	$ 1.0
Income Statement Related Disclosures [Abstract]
Deferred revenue				10.0
AbbVie \| AbbVie Tau Collaboration Agreement
Allocable arrangement consideration
Non-refundable upfront payment received		$ 69.0
Income Statement Related Disclosures [Abstract]
Revenue recognized				11.3	$ 6.9
Deferred revenue				$ 50.8
Number of development options \| item		3

Commitments and contingencies - AbbVie Alpha Synuclein Collaboration Agreement - (Details) - AbbVie Alpha Synuclein Collaboration Agreement - AbbVie $ in Thousands	1 Months Ended	12 Months Ended
	Feb. 28, 2019 USD ($) item	Dec. 31, 2019 USD ($) 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
Deferred revenue		$ 63,700
Revenue recognized		$ 1,300
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	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

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

Common stock (Details)	12 Months Ended
Common stock (Details)	Dec. 31, 2019 Vote $ / shares shares	Dec. 31, 2018 $ / shares shares	Oct. 31, 2015 shares
Class of Stock [Line Items]
Common Stock, Shares Authorized	120,000,000	120,000,000
Common stock, par value (in dollars per share) \| $ / shares	$ 0.001	$ 0.001
Number of votes entitled for each share of common stock \| Vote	1
Dividends declared \| $ / shares	$ 0
Dividends paid \| $ / shares	$ 0
Shares available for future issuance (in shares)	9,043,155	7,397,059
2015 Stock Option Plan
Class of Stock [Line Items]
Shares available for future issuance (in shares)	1,875,078		1,311,812
Vesting of restricted stock awards \| Founder Awards
Class of Stock [Line Items]
Shares available for future issuance (in shares)	176,471	235,294
Exercise of stock options
Class of Stock [Line Items]
Shares available for future issuance (in shares)	5,317,326	4,225,152
Vesting of restricted stock units
Class of Stock [Line Items]
Shares available for future issuance (in shares)	455,404
Issuance under share based compensation plans \| 2015 Stock Option Plan
Class of Stock [Line Items]
Shares available for future issuance (in shares)	1,875,078	1,973,227
Issuance under share based compensation plans \| 2015 Employee Stock Purchase Plan
Class of Stock [Line Items]
Shares available for future issuance (in shares)	1,218,876	963,386

401(k) Savings Plan (Details) - USD ($) $ in Millions	12 Months Ended
401(k) Savings Plan (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
401(k) Savings Plan
Employer contribution expense	$ 1.0	$ 0.8	$ 0.5

Income taxes (Details) $ in Thousands	12 Months Ended
Income taxes (Details) $ in Thousands	Dec. 31, 2018 USD ($)
Current
Federal	$ 180
Total current	180
Total tax expense	$ 180

Income taxes - Net operating loss carryforwards (Details) $ in Thousands			12 Months Ended
	May 03, 2019 item	Dec. 31, 2017	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017	Dec. 31, 2016 item
Operating Loss Carryforwards [Line Items]
Valuation Allowance			$ 90,920	$ 75,213
Change in the valuation allowance			$ 15,700
Duration for payable unrepatriated earnings					8 years
Number of ownership changes \| item	0					3
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Income tax computed at federal statutory tax rate		35.00%	21.00%	21.00%	34.00%
General business credit carryovers			9.40%	3.10%	5.00%
State taxes, net of federal benefit			8.00%	6.30%	6.10%
Deferred rate change					(21.80%)
Nondeductible expenses			(2.20%)	(2.10%)	(4.10%)
Change in valuation allowance			(36.20%)	(28.10%)	(19.20%)
Total				0.20%
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards			$ 182,400
Maximum NOL carryforwards (as a percent)			80.00%
State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards			$ 180,400
Investment Tax Credit expiring in 2019			600
Tax Year 2019 \| Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards			19,100
Tax Year 2019 \| State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards			16,100
Research and development tax credits carryforwards \| Federal
Operating Loss Carryforwards [Line Items]
Tax credits carryforwards			13,400
Research and development tax credits carryforwards \| State
Operating Loss Carryforwards [Line Items]
Tax credits carryforwards			$ 4,300

Related party transactions (Details) $ in Millions	12 Months Ended
Related party transactions (Details) $ in Millions	Dec. 31, 2019 USD ($) item	Dec. 31, 2018 USD ($) item
Investor \| Consulting and management services
Related party transactions
Number of individuals providing services \| item	1	1
Former Executives \| Board and scientific advisory services
Related party transactions
Number of individuals providing services \| item	2	2
Total amount of services received \| $	$ 0.4	$ 0.1
Neurocrine Collaboration Agreement \| Neurocrine
Related party transactions
Reimbursement costs expected to be received \| $	$ 18.5

Selected quarterly financial data (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Selected quarterly financial data (unaudited)
Collaboration revenue	$ 32,674	$ 20,433	$ 46,087	$ 5,197	$ 2,008	$ 2,094	$ 2,575	$ 942	$ 104,391	$ 7,619	$ 10,135
Total operating expenses	46,442	38,240	36,898	34,490	25,169	23,241	28,269	22,035	156,070	98,714	81,998
Loss from operations	(13,768)	(17,807)	9,189	(29,293)	(23,161)	(21,147)	(25,694)	(21,093)	(51,679)	(91,095)	(71,863)
Net (loss) income	$ (12,574)	$ (15,006)	$ 11,153	$ (27,170)	$ (22,532)	$ (20,289)	$ (25,541)	$ (19,926)	$ (43,597)	$ (88,288)	$ (70,698)
Net (loss) income per share	$ (0.34)	$ (0.41)	$ 0.30	$ (0.81)	$ (0.70)	$ (0.63)	$ (0.80)	$ (0.63)	$ (1.21)	$ (2.75)	$ (2.64)