Voyager Therapeutics (VYGR) 10-Q 7 May 19 2019 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2019	May 03, 2019
Document and Entity Information
Entity Registrant Name	Voyager Therapeutics, Inc.
Entity Central Index Key	0001640266
Document Type	10-Q
Document Period End Date	Mar. 31, 2019
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Common Stock, Shares Outstanding		36,832,397
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 113,261	$ 46,859
Marketable securities, current	245,238	108,947
Prepaid expenses and other current assets	6,668	6,675
Total current assets	365,167	162,481
Property and equipment, net	13,146	12,771
Deposits and other non-current assets	1,462	1,149
Operating lease, right-of-use asset	30,294
Marketable securities, non-current	1,280	628
Total assets	411,349	177,029
Current liabilities:
Accounts payable	2,261	1,038
Accrued expenses	9,276	9,788
Other current liabilities	2,673
Deferred revenue, current portion	44,566	20,847
Total current liabilities	58,776	31,673
Deferred revenue, net of current portion	217,483	92,199
Other non-current liabilities	34,396	6,711
Total liabilities	310,655	130,583
Commitments and contingencies (see note 7)
Stockholders’ equity:
Preferred stock, $0.001 par value: 5,000,000 shares authorized at March 31, 2019 and December 31, 2018; no shares issued and outstanding at March 31, 2019 and December 31, 2018
Common stock, $0.001 par value: 120,000,000 shares authorized at March 31, 2019 and December 31, 2018; 36,575,983 and 32,364,895 shares issued and outstanding at March 31, 2019 and December 31, 2018, respectively	37	32
Additional paid-in capital	396,953	315,598
Accumulated other comprehensive loss	(75)	(133)
Accumulated deficit	(296,221)	(269,051)
Total stockholders’ equity	100,694	46,446
Total liabilities and stockholders’ equity	$ 411,349	$ 177,029

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2019	Dec. 31, 2018
Condensed Consolidated Balance Sheets
Preferred Stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred Stock, Shares Authorized	5,000,000	5,000,000
Preferred Stock, Shares Issued	0	0
Preferred Stock, Shares Outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common Stock, Shares Authorized	120,000,000	120,000,000
Common Stock, Shares, Issued	36,575,983	32,364,895
Common Stock, Shares, Outstanding	36,575,983	32,364,895

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Collaboration revenue	$ 5,197	$ 942
Operating expenses:
Research and development	24,831	14,853
General and administrative	9,659	7,182
Total operating expenses	34,490	22,035
Operating loss	(29,293)	(21,093)
Other income:
Interest income	1,145	588
Other income	978	399
Total other income	2,123	987
Loss before income taxes	(27,170)	(20,106)
Income tax benefit		180
Net loss	(27,170)	(19,926)
Other comprehensive income
Net unrealized gain on available-for-sale-securities	58	5
Cumulative-effect adjustment resulting from ASU No. 2016-01		(20,050)
Total other comprehensive income	58	125
Comprehensive loss	$ (27,112)	$ (19,801)
Net loss per share, basic and diluted	$ (0.81)	$ (0.63)
Weighted-average common shares outstanding, basic and diluted	33,353,061	31,759,870
ASU 2016-01
Other comprehensive income
Cumulative-effect adjustment resulting from ASU No. 2016-01		$ 120

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit	Total
Stockholders' Equity, Beginning Balance at Dec. 31, 2017	$ 32	$ 295,019	$ (287)	$ (160,713)	$ 134,051
Shares, Outstanding, Beginning Balance at Dec. 31, 2017	31,572,044
Vesting of restricted stock		3			3
Vesting of restricted stock (in shares)	145,829
Exercises of vested stock options		1,412			1,412
Exercises of vested stock options (in shares)	132,733
Issuance of common stock under ESPP		418			418
Issuance of common stock under ESPP (in shares)	38,392
Stock based compensation expense		2,260			2,260
Unrealized gain (loss) on available for-sale securities, net of tax			5		5
Impact of adopting new accounting standards | ASU 2016-01			120	(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				(19,926)	(19,926)
Stockholders' Equity, Ending Balance at Mar. 31, 2018	$ 32	299,112	(162)	(200,689)	98,293
Shares, Outstanding, Ending Balance at Mar. 31, 2018	31,888,998
Stockholders' Equity, Beginning Balance at Dec. 31, 2018	$ 32	315,598	(133)	(269,051)	46,446
Shares, Outstanding, Beginning Balance at Dec. 31, 2018	32,364,895
Exercises of vested stock options	$ 1	283			$ 284
Exercises of vested stock options (in shares)	31,360				31,360
Issuance of common stock in connection with Neurocrine Collaboration Agreement	$ 4	77,613			$ 77,617
Issuance of common stock in connection with Neurocrine Collaboration Agreement (in shares)	4,179,728
Stock based compensation expense		3,459			3,459
Unrealized gain (loss) on available for-sale securities, net of tax			58		58
Net loss				(27,170)	(27,170)
Stockholders' Equity, Ending Balance at Mar. 31, 2019	$ 37	$ 396,953	$ (75)	$ (296,221)	$ 100,694
Shares, Outstanding, Ending Balance at Mar. 31, 2019	36,575,983

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flow from operating activities
Net loss	$ (27,170)	$ (19,926)
Adjustments to reconcile net loss to net cash provided by operating activities:
Stock-based compensation expense	3,518	2,322
Depreciation	616	456
Amortization of premiums and discounts on marketable securities	(554)	(309)
In-kind research and development expenses	392	176
Other non-cash items	(965)	(591)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	7	305
Operating lease, right-of-use asset	670
Accounts payable	1,223	352
Accrued expenses	(580)	(2,232)
Operating lease liabilities	(606)
Deferred revenue	148,611	68,057
Net cash provided by operating activities	125,162	48,610
Cash flow from investing activities
Purchases of property and equipment	(1,104)	(1,607)
Loss from sale of equipment	122
Purchases of marketable securities	(214,979)	(9,991)
Proceeds from maturities of marketable securities	79,300	70,000
Net cash (used in) provided by investing activities	(136,661)	58,402
Cash flow from financing activities
Proceeds from the exercise of stock options	284	1,411
Proceeds from the issuance of common stock in connection with the Neurocrine Collaboration Agreement	77,617
Proceeds from the purchase of common stock under ESPP		418
Net cash provided by financing activities	77,901	1,829
Net increase in cash and cash equivalents	66,402	108,841
Cash, cash equivalents, and restricted cash beginning of period	47,594	32,265
Cash, cash equivalents, and restricted cash end of period	113,996	141,106
Supplemental disclosure of cash and non-cash activities
Capital expenditures incurred but not yet paid	$ 9	25
Impact of adopting new accounting standards		$ 20,050

Nature of business

Nature of business	3 Months Ended
	Mar. 31, 2019
Nature of business
Nature of business	VOYAGER THERAPEUTICS INC. NOTE 1. Nature of business Voyager Therapeutics, Inc. (the “Company”) is a clinical-stage gene therapy company focused on developing life-changing treatments for patients suffering from severe neurological diseases. The Company is focused on neurological diseases where it believes an adeno-associated virus (“AAV”) gene therapy approach that either increases or decreases the production of a specific protein can slow or reduce the symptoms experienced by patients, and therefore have a clinically meaningful impact. The Company has built a gene therapy platform that it believes positions itself to be a leading company at the intersection of AAV gene therapy and severe neurological disease. The Company’s gene therapy platform enables it to engineer, optimize, manufacture and deliver its AAV-based gene therapies that have the potential to provide durable efficacy following a single administration. Additionally, the Company is working to identify novel AAV capsids, which are the outer viral protein shells that enclose the genetic material of the virus payload. The Company’s team of experts in the fields of AAV gene therapy and neuroscience first identifies and selects severe neurological diseases that are well-suited for treatment using AAV gene therapy. The Company then engineers and optimizes AAV vectors for delivery of the virus payload to the targeted tissue or cells. The Company’s manufacturing process employs an established system that it believes will enable production of high quality AAV vectors at commercial-scale. I n addition to the Company’s capsid optimization efforts, it leverages novel delivery paradigms, established routes of administration, and advances in dosing techniques to optimize delivery of its AAV gene therapies to target tissues, regions and cell types that are critical to the disease of interest. The Company believes it can achieve this directly, with targeted infusions to discrete regions of the brain or spinal cord, or systemically, in conjunction with its novel capsids. The Company’s business strategy focuses on discovering, developing, manufacturing, and commercializing its gene therapy programs. As part of this strategy, the Company has developed core competencies specific to AAV gene therapy development and manufacturing and is beginning to build its commercial infrastructure. This business strategy also includes business development activities that may include in-licensing activities or partnering certain programs in certain geographies with collaborators, as the Company has demonstrated through its collaboration with Sanofi Genzyme (the “ Sanofi Genzyme Collaboration”), its collaboration with AbbVie Biotechnology Ltd (the “ AbbVie Tau Collaboration”), its collaboration with AbbVie Ireland Unlimited Company (the “AbbVie Alpha-Synuclein Collaboration”), and its collaboration with Neurocrine Biosciences, Inc. (the “Neurocrine Collaboration”). The Company is devoting substantially all of its efforts to product research and development, market development, and raising capital. The Company is subject to risks common to companies in the biotechnology and gene therapy industry, including but not limited to, the need to obtain sufficient capital to continue to fund its operations, risks of failure of preclinical studies and clinical trials, the need to obtain marketing approval for its product candidates, the need to successfully commercialize and gain market acceptance of its product candidates, dependence on key personnel, protection of proprietary technology, compliance with government regulations, development by competitors of technological innovations, and ability to transition from pilot-scale manufacturing to large-scale production of products. The Company has incurred annual net operating losses in every year since inception. As of March 31, 2019, the Company had an accumulated deficit of $296.2 million. The Company has not generated any product revenue and has financed its operations primarily through public offerings, private placements of its equity securities, and funding from its collaborations with Sanofi Genzyme, AbbVie Biotechnology Ltd and AbbVie Ireland Unlimited Company (collectively, “AbbVie”), and Neurocrine . Through March 31, 2019, the Company has raised approximately $635.0 million of proceeds from sales of convertible preferred stock and common stock, including its initial public offering and follow-on public offering, and proceeds from collaboration agreements. The Company believes that its cash, cash equivalents, and marketable debt securities of $358.5 million as of March 31, 2019, as well as amounts expected to be received for reimbursement of development costs from the Neurocrine Collaboration Agreement, are sufficient to fund its operating expenses and capital expenditure requirements into mid-2022. There can be no assurance that the Company will be able to obtain additional debt or equity financing or generate product revenue or revenue from collaborative partners on terms acceptable to the Company, on a timely basis or at all. The failure of the Company to obtain sufficient funds on acceptable terms when needed could have a material adverse effect on the Company’s business, results of operations, and financial condition.

Summary of significant accounti

Summary of significant accounting policies	3 Months Ended
	Mar. 31, 2019
Summary of significant accounting policies
Summary of significant accounting policies	2. Summary of significant accounting policies and basis of presentation Basis of presentation The accompanying unaudited condensed consolidated financial statements of the Company have been prepared in accordance with accounting principles generally accepted in the United States (“GAAP”) for interim financial reporting and as required by Regulation S-X, Rule 10-01. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. For further information, refer to the consolidated financial statements and footnotes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018 as filed with the Securities and Exchange Commission (“SEC”) on February 26, 2019. These interim condensed consolidated financial statements, in the opinion of management, reflect all normal recurring adjustments necessary for a fair presentation of the Company’s financial position and results of operations for the periods presented. Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASU”) of the Financial Accounting Standards Board (“FASB”). See “ Recently Adopted Accounting Pronouncements ” below for discussion of the Company’s adoption of new guidance effective January 1, 2019. All amounts and disclosures set forth in this Quarterly Report on Form 10-Q reflect adoption of these changes. Principles of consolidation The unaudited interim consolidated financial statements include the accounts of the Company and its wholly owned subsidiary as disclosed in Note 2, Summary of Significant Accounting Policies, within the “Notes to Consolidated Financial Statements” accompanying the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2018. Intercompany accounts and transactions have been eliminated. Use of estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. On an ongoing basis, the Company’s management evaluates its estimates, which include, but are not limited to, estimates related to revenue recognition, accrued expenses, stock-based compensation expense, and income taxes. The Company bases its estimates on historical experience and other market specific or other relevant assumptions that it believes to be reasonable under the circumstances. Actual results may differ from those estimates or assumptions. Certain reclassifications have been made to prior periods to conform to current period presentation. Leases Effective January 1, 2019, the Company accounted for its operating leases in accordance with ASC Topic 842 Leases (“ASC 842”). ASC 842 provides guidance on accounting for lease arrangements by both lessors and lessees and requires lessees to recognize a lease liability and a right-of-use asset for most leases. The Company determines if an arrangement is a lease at inception. The Company’s operating leases are included in operating lease right-of-use (“ROU”) assets, other current liabilities, and other non-current liabilities on the consolidated balance sheets. ROU assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating lease ROU assets and liabilities are recognized at adoption date based on the present value of lease payments over the lease term. As the Company’s leases do not provide an implicit rate, an incremental borrowing rate was used based on the information available at the lease commencement date in determining the present value of lease payments. On future lease obligations, the implicit rate will be set when readily determinable. The operating lease ROU assets also include the effect of any lease payments made and exclude lease incentives. The Company’s lease terms may include options to extend or terminate the lease even when it is not reasonably certain that the option will be exercised. Lease expense for lease payments is recognized on a straight-line basis over the lease term. The Company has lease agreements with lease and non-lease components, which are accounted for separately. Non-lease components generally refer to common area maintenance charges related to the premises. Revenue recognition The Company enters into collaboration agreements which are within the scope of ASC 606, Revenue from Contracts with Customers (“ASC 606”), under which the Company licenses rights to certain of the Company’s product candidates and performs research and development services. The terms of these arrangements typically include payment of one or more of the following: non-refundable, upfront fees; reimbursement of research and development costs; development, regulatory, and commercial milestone payments; and royalties on net sales of licensed products. Under ASC 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine the appropriate amount of revenue to be recognized for arrangements determined to be within the scope of ASC 606, the Company performs the following five steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect consideration it is entitled to in exchange for the goods or services it transfers to the customer. The promised goods or services in 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. Stock‑based compensation expense The Company accounts for its stock‑based compensation awards in accordance with ASC Topic 718 Compensation—Stock Compensation (“ASC 718”). ASC 718 requires all stock‑based payments to employees, nonemployees, and directors, including grants of restricted stock units and stock options, to be recognized as expense in the statements of operations based on their grant date fair values. The Company estimates the fair value of options granted using the Black‑Scholes option pricing model. The Company uses the fair value of its common stock on the grant date to determine the fair value of restricted stock units. The Black‑Scholes option pricing model requires inputs based on certain subjective assumptions, including (a) the expected stock price volatility, (b) the calculation of expected term of the award, (c) the risk‑free interest rate and (d) expected dividends. Due to a lack of company-specific historical and implied volatility data, the Company bases the estimate of expected volatility on the historical volatility of a group of similar companies that are publicly traded, blended with the most recent period of historic volatility of its common stock. The historical volatility is calculated based on a period of time commensurate with the expected term assumption. The computation of expected volatility is based on the historical volatility of a representative group of companies with similar characteristics to the Company, including stage of product development and life science industry focus. The Company uses the simplified method as prescribed by the SEC Staff Accounting Bulletin No. 107, Share‑Based Payment , to calculate the expected term for stock options granted to employees as it does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term. For stock options granted to non‑employees, the Company utilizes the contractual term of the arrangement as the basis for the expected term assumption. The risk‑free interest rate is based on a treasury instrument whose term is consistent with the expected term of the stock options. The expected dividend yield is assumed to be zero as the Company has never paid dividends and has no current plans to pay any dividends on its common stock. The Company expenses the fair value of its stock‑based compensation awards on a straight‑line basis over the associated service period, which is generally the period in which the related services are received. The Company records the expense for stock‑based compensation awards subject to performance conditions over the remaining service period when management determines that achievement of the performance condition is probable. Management evaluates if the achievement of a performance condition is probable based on the expected satisfaction of the performance conditions as of the reporting date. Recently Adopted Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, a comprehensive new lease accounting standard, which provides revised guidance on accounting for lease arrangements by both lessors and lessees and requires lessees to recognize a lease liability and a right-of-use asset for most leases. In July 2018, the FASB issued ASU No. 2018-11, Leases (“ASC 842”), Targeted Improvements , which provides an additional transition method that allowed entities to initially apply the new lease requirements at the adoption date, not the earliest period presented, and recognize a cumulative effect adjustment to the opening balance of retained earnings in the period of adoption. The Company elected this transition method at the adoption date of January 1, 2019. The Company elected a package of practical expedients, under which an entity need not reassess whether any expired or existing contracts are or contain leases, the lease classification for any expired or existing leases, or initial direct costs for any existing leases. The impact of adopting ASC 842 was represented as a capitalization of a right-of-use asset of approximately $31.0 million with a corresponding lease liability of approximately $36.7 million to be recognized over the remaining life of the Company’s leases. In June 2018, the FASB issued ASU No. 2018-07, Compensation-Stock Compensation: Improvements to Nonemployee Share-Based Payment Accounting (“ASC 718”). 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 this ASC on January 1, 2019 did not have a material impact on the Company's consolidated financial statements. Recent Accounting Pronouncements In August 2018, the FASB issued ASU No. 2018-13, Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement (“ASU 2018-13”). This standard eliminates, adds and modifies certain disclosure requirements for fair value measurements as part of its disclosure framework project. ASU 2018-13 is effective for annual reporting periods beginning after December 15, 2019 and interim periods within those annual periods and early adoption is permitted. The Company is currently evaluating the potential impact that this guidance may have on its consolidated financial statements. In June 2016, the FASB issued ASU No. 2016-13, Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”). ASU 2016-13 will change how companies account for credit losses for most financial assets and certain other instruments. For trade receivables, loans and held-to-maturity debt securities, companies will be required to recognize an allowance for credit losses rather than reducing the carrying value of the asset. ASU 2016-13 is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted. The Company is currently evaluating the potential impact that this guidance may have on its consolidated financial statements.

Fair value measurements

Fair value measurements	3 Months Ended
	Mar. 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 March 31, 2019 and December 31, 2018 are as follows: Quoted Prices Significant in Active Other Significant Markets for Observable Unobservable Identical Assets Inputs Inputs Assets Total (Level 1) (Level 2) (Level 3) March 31, 2019 (in thousands) Money market funds included in cash and cash equivalents $ 112,872 $ 112,872 $ — $ — Marketable securities: U.S. Treasury notes 245,238 245,238 — — Equity securities 1,280 1,280 — — Total marketable securities $ 246,518 $ 246,518 $ — $ — Warrants to purchase equity securities 547 — 547 — Total $ 359,937 $ 359,390 $ 547 $ — December 31, 2018 Money market funds included in cash and cash equivalents $ 46,173 $ 46,173 $ — $ — Marketable securities: U.S. Treasury notes 108,947 108,947 — — Equity securities 628 628 — — Total marketable securities $ 109,575 $ 109,575 $ — $ — Warrants to purchase equity securities 234 — 234 — Total $ 155,982 $ 155,748 $ 234 $ — The Company measures the fair value of money market funds, U.S. Treasury notes and equity securities based on quoted prices in active markets for identical securities. The Level 2 equity securities include warrants used to purchase equity securities that are valued using the Black-Scholes model. The Black-Scholes option pricing model requires inputs based on certain subjective assumptions, including (a) the expected stock price volatility, (b) the calculation of expected term of the awards, (c) the risk-free interest rate, and (d) expected dividends. The assumptions utilized to value the warrants to purchase equity securities as of March 31, 2019 and December 31, 2018 are as follows: As of March 31, As of December 31, 2019 2018 Risk-free interest rate 2.2 % 2.5 % Expected dividend yield — % — % Expected term (in years) 2.4 2.7 Expected volatility 103.7 % 112.7 % The expected volatility is based on the historic volatility for the equity securities underlying the warrants and is calculated based on a period of time commensurate with the expected term assumption. The expected term is based on the remaining contractual life of the warrants on each measurement date. The risk-free interest rate is based on a treasury instrument whose term is consistent with the expected term of the warrants. The expected dividend yield is assumed to be zero as the entity that issued the warrants has never paid and has not indicated any intention to pay dividends.

Cash, cash equivalents, restric

Cash, cash equivalents, restricted cash, and available for sale marketable securities	3 Months Ended
	Mar. 31, 2019
Cash, cash equivalents, restricted cash, and available for sale marketable securities
Cash, cash equivalents, restricted cash, and available for sale marketable securities	4. Cash, cash equivalents, restricted cash, and available-for-sale marketable securities Cash equivalents include all highly liquid investments maturing within 90 days from the date of purchase. Investments consist of securities with original maturities greater than 90 days when purchased. The Company classifies these investments as available-for-sale and records them at fair value in the accompanying condensed consolidated balance sheets. Unrealized gains or losses are included in accumulated other comprehensive income (loss). Premiums or discounts from par value are amortized to investment income over the life of the underlying investment. The Company classifies marketable debt securities with a remaining maturity when purchased of greater than three months as available ‑ for ‑ sale. Marketable debt securities with a remaining maturity date greater than one year and marketable equity securities are classified as non ‑ current where the Company has the intent and ability to hold these securities for at least the next 12 months. Available ‑ for ‑ sale debt securities are maintained by an investment manager and consist of U.S. Treasury notes. In 2016, the Company invested in a supplier and received common stock and warrants to purchase common stock in that entity. The common stock is included in non-current marketable securities and the warrants are included in non-current assets. All available ‑ for ‑ sale securities are carried at fair value with the unrealized gains and losses included in other comprehensive income (loss) as a component of stockholders’ equity until realized. Any premium or discount arising at purchase is amortized and/or accreted to interest income and/or expense. Realized gains and losses are determined using the specific identification method and are included in other income (expense). If any adjustment to fair value reflects a decline in value of the investment, the Company considers all available evidence to evaluate the extent to which the decline is “other ‑ than ‑ temporary” and, if so, recognizes the unrealized loss through a charge to the Company’s statement of operations and comprehensive loss. No other than temporary losses have been recognized. Cash, cash equivalents, and marketable securities included the following at March 31, 2019 and December 31, 2018: Amortized Unrealized Unrealized Fair Cost Gains Losses Value (in thousands) As of March 31, 2019 Money market funds included in cash and cash equivalents $ 112,872 $ — $ — $ 112,872 Marketable securities: U.S. Treasury notes 245,186 52 — 245,238 Equity securities 1,220 60 — 1,280 Total marketable securities $ 246,406 $ 112 $ — $ 246,518 Total money market funds and marketable securities $ 359,278 $ 112 $ — $ 359,390 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 March 31, 2019, have a contractual maturity of one year or less. The following table provides a reconciliation of cash, cash equivalents, and restricted cash within the condensed consolidated balance sheets that sum to the total of the same such amounts shown in the condensed consolidated statements of cash flows: As of March 31, 2019 2018 (in thousands) Cash and cash equivalents $ 113,261 $ 140,371 Restricted cash included in deposits and other non-current assets 735 735 Total cash, cash equivalents, and restricted cash $ 113,996 $ 141,106

Accrued expenses

Accrued expenses	3 Months Ended
	Mar. 31, 2019
Accrued expenses
Accrued expenses	5. Accrued expenses Accrued expenses as of March 31, 2019 and December 31, 2018 consist of the following: As of March 31, As of December 31, 2019 2018 (in thousands) Research and development costs $ 4,922 $ 3,555 Employee compensation costs 1,904 3,780 Professional services 1,445 1,448 Accrued goods and services 879 784 Patent costs 70 120 Other 56 101 Total $ 9,276 $ 9,788

Right-of-use asset and lease li

Right-of-use asset and lease liabilities	3 Months Ended
	Mar. 31, 2019
Right-of-use asset and lease liabilities
Right-of-use asset and lease liabilities	6. Right-of-use asset and lease liabilities The Company adopted ASC 842, which requires balance sheet recognition for leases. The Company adopted the standard using the modified retrospective approach with an effective date as of the beginning of the Company’s fiscal year, January 1, 2019. Prior year interim periods were not recast under the new standard and therefore, those amounts are not presented below. The Company elected to utilize practical expedients available for expired or existing contracts which allowed the Company to carryforward historical assessments of (1) whether contracts are or contain leases, (2) lease classification, and (3) initial direct costs. Operating Leases During April 2014, the Company entered into an agreement to lease its 75 Sidney Street facility under a non‑cancelable operating lease that would have expired, if not subsequently extended, on December 15, 2019. The lease includes two renewal options, each for five-year terms and at fair market value upon exercise. The lease contains escalating rent clauses which require higher rent payments in future years. The Company expenses rent on a straight‑line basis over the term of the lease, including any rent‑free periods. In December 2015, the Company executed an amendment to extend the term of the 75 Sidney Street lease and also executed an agreement to lease an additional facility at 64 Sidney Street until December 31, 2024. The facility at 64 Sidney Street includes laboratory and office space and was ready for occupancy in early 2017. In February 2018, the Company executed a second amendment to the 75 Sidney Street lease to lease additional space to support its continued growth. The additional facility includes laboratory and office space and was ready for occupancy in mid-2018. In June 2018, the Company executed a third amendment to the 75 Sidney Street lease to lease additional space to further support its continued growth. The additional facility includes laboratory and office space, and was ready for occupancy in late 2018. The third amendment extended the term of the 75 Sidney Street lease to November 30, 2026. Additionally, the Company executed a second amendment to the 64 Sidney Street lease to extend that lease to November 30, 2026. The Company has received leasehold improvement incentives from the landlord totaling $1.3 million and $3.5 million for 75 Sidney Street and 64 Sidney Street, respectively. The Company recorded these incentives as a component of its ROU asset and is amortizing these incentives as a reduction of rent expense over the life of the leases. The leasehold improvements have been capitalized as fixed assets. The Company is entitled to receive approximately $0.3 million of leasehold improvements for the additional space at 75 Sidney Street acquired under the third amendment to the 75 Sidney Street lease. The Company’s lease agreements require the Company to maintain a cash deposit or irrevocable letter of credit of $0.7 million payable to the landlord as security for the performance of its obligations under the leases. These amounts are recorded as restricted cash and included in deposits and other non-current assets in the accompanying balance sheets. The following table summarizes the Company’s significant contractual obligations under operating leases as of payment due date by period at March 31, 2019: Total Minimum Lease Payments (in thousands) 2019 (remainder of year) $ 4,134 2020 5,960 2021 6,138 2022 6,323 2023 6,512 2024+ 20,897 $ 49,964 During the three months ended March 31, 2019 and 2018, the Company incurred rent expense of $1.4 million and $0.8 million, respectively, for operating leases. As of March 31, 2019, the weighted average remaining lease term was 7.7 years and the weighted average incremental borrowing rate used to determine the operating lease liability was 8.5%.

Commitments and contingencies

Commitments and contingencies	3 Months Ended
	Mar. 31, 2019
Commitments and contingencies
Commitments and contingencies	7. Commitments and contingencies Significant Agreements Sanofi Genzyme Collaboration Agreement Summary of Agreement In February 2015, the Company entered into a collaboration agreement with Sanofi Genzyme (the “Sanofi Genzyme Collaboration Agreement”) which included a non‑refundable upfront payment of $65.0 million. In addition, contemporaneously with entering into the Sanofi Genzyme Collaboration Agreement, Sanofi Genzyme entered into a Series B Stock Purchase Agreement, under which Sanofi Genzyme purchased 10,000,000 shares of Series B Preferred Stock for $30.0 million. The fair value of the Series B Preferred Stock at the time of issuance was approximately $25.0 million. The $5.0 million premium over the fair value was accounted for as additional consideration under the Sanofi Genzyme Collaboration Agreement. Under the Sanofi Genzyme Collaboration Agreement, the Company granted Sanofi Genzyme an exclusive option to license, develop, and commercialize (i) ex‑U.S. rights to the following programs, which are referred to as “Split Territory Programs”; VY‑AADC (“Parkinson’s Program”), VY‑FXN01 (“Friedreich’s ataxia Program”), a future program to be designated by Sanofi Genzyme (“ Future Program”), and VY‑HTT01 (“Huntington’s Program”), with an incremental option to co‑commercialize VY‑HTT01 in the United States and (ii) worldwide rights to VY‑SMN101 (“Spinal Muscular Atrophy Program”). Sanofi Genzyme ’s option for the Split Territory Programs and the Spinal Muscular Atrophy Program is triggered following the completion of the first proof‑of‑principle human clinical study (“POP Study”), on a program-by-program basis. Prior to any option exercise by Sanofi Genzyme , the Company will collaborate with Sanofi Genzyme in the development of products under each Split Territory Program and the Spinal Muscular Atrophy Program pursuant to a written development plan and under the guidance of an Alliance Joint Steering Committee (“AJSC”), comprised of an equal number of employees from the Company and Sanofi Genzyme . The Company is required to use commercially reasonable efforts to develop products under each Split Territory Program and the Spinal Muscular Atrophy Program through the completion of the applicable POP Study. During the development of these joint programs, the activities are guided by a Development Advisory Committee (“DAC”). The DAC may elect to utilize certain Sanofi Genzyme technology relating to the Parkinson’s Program, the Huntington’s Program, or generally with the manufacture of Split Territory Program products. The Company is 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 will provide “in‑kind” services valued at up to $5.0 million and (ii) Sanofi Genzyme shall be responsible for the costs and expenses of activities under the Huntington’s Program development plan to the extent such activities are covered by financial support Sanofi Genzyme is entitled to receive from a patient advocacy group. Other than the Parkinson’s Program (for which a POP Study has already been completed), if the Company does not initiate a POP Study for a given Split Territory Program by December 31, 2026 (or for the Future Program by the tenth anniversary of the date the Future Program is nominated by Sanofi Genzyme ), and Sanofi Genzyme has not terminated the Sanofi Genzyme Collaboration Agreement with respect to the collaboration program, then Sanofi Genzyme shall be entitled, as its sole and exclusive remedy, to a credit of $10.0 million for each such program against other milestone or royalty payments payable by Sanofi Genzyme under the Sanofi Genzyme Collaboration Agreement. However, if the POP Study is not initiated due to a regulatory delay or a force majeure event, such time period shall be extended for so long as such delay continues. With the exception of the Parkinson’s Program, Sanofi Genzyme is required to pay an option exercise payment of $20.0 million or $30.0 million for each Split Territory Program and Spinal Muscular Atrophy Program. Upon Sanofi Genzyme ’s exercise of its option to license a given product in a Split Territory Program (“Split Territory Licensed Product”), the Company will have sole responsibility for the development of such Split Territory Licensed Product in the United States and Sanofi Genzyme shall have sole responsibility for development of such Split Territory Licensed Product in the rest of the world. The Company and Sanofi Genzyme will have shared responsibility for execution of ongoing development of such Split Territory Licensed Product that is not specific to either territory, including costs associated therewith. The Company is responsible for all commercialization activities relating to Split Territory Licensed Products in the United States, including all of the associated costs. Sanofi Genzyme is responsible for all commercialization activities relating to the Split Territory Licensed Products in the rest of the world, including all of the associated costs. If Sanofi Genzyme exercises its co‑commercialization rights with respect to VY-HTT01, Sanofi Genzyme will be the lead party responsible for all commercialization activities related to the VY-HTT01 product in the United States. Upon exercise of the option to license a product in the Spinal Muscular Atrophy Program, Sanofi Genzyme shall have the sole right to develop the Spinal Muscular Atrophy licensed product worldwide. Sanofi Genzyme shall be responsible for all of the development costs that occur after the option exercise date for the Spinal Muscular Atrophy Program. Sanofi Genzyme is also responsible for commercialization activities relating to the Spinal Muscular Atrophy licensed product worldwide. Sanofi Genzyme is required to pay the Company for specified regulatory and commercial milestones, if achieved, up to $540.0 million across all programs. The Company is no longer entitled to receive a total of $105.0 million related to regulatory and commercial milestone payments for VY-AADC as a result of Sanofi Genzyme’s decision in October 2017 to not exercise its option for the Parkinson’s Program (the “PD Opt-Out”). The remaining regulatory approval milestones are payable upon either regulatory approval in the United States or regulatory and reimbursement approval in the European Union and range from $40.0 million to $50.0 million per milestone, with an aggregate total of $220.0 million, after accounting for the PD Opt-Out. The remaining commercial milestones are payable upon achievement of specified annual net sales in each program and range from $50.0 million to $100.0 million per milestone, with an aggregate total of $320.0 million, after accounting for the PD Opt-Out . In addition, to the extent any Split Territory Licensed Products or the Spinal Muscular Atrophy licensed product are commercialized, the Company is entitled to tiered royalty payments ranging from the mid‑single digits to mid‑teens based on a percentage of net sales by Sanofi Genzyme . Sanofi Genzyme is entitled to receive tiered royalty payments related to sales of the Split Territory Licensed Product ranging from the low‑single digits to mid‑single digits based on a percentage of net sales by the Company depending on whether the Company uses Sanofi Genzyme technology in the Split Territory Licensed Product. If Sanofi Genzyme elects to co‑commercialize VY‑HTT01 in the United States, the Company and Sanofi Genzyme will share in any profits or losses from VY‑HTT01 product sales. The Sanofi Genzyme Collaboration Agreement will continue in effect until the later of (i) the expiration of the last to expire of the option rights and (ii) the expiration of all payment obligations unless sooner terminated by the Company or Sanofi Genzyme . The Company and Sanofi Genzyme have customary termination rights including the right to terminate for an uncured material breach of the agreement committed by the other party and Sanofi Genzyme has the right to terminate for convenience. Accounting Analysis At inception, the Sanofi Genzyme Collaboration Agreement included the following performance obligations: (i) research and development services for each of the Split Territory Programs and the Spinal Muscular Atrophy Program, (ii) participation in the AJSC, (iii) participation in the DAC and (iv) a material right associated with an option to obtain a development and commercial license in the Parkinson’s Program (“PD Material Right”). The Company determined that the option to obtain a development and commercial license in the Parkinson’s Program was a material right under ASC 606 primarily because there were no additional option exercise payments payable by Sanofi Genzyme at the time of option exercise. Therefore, the PD Material Right was considered a performance obligation at the inception of the arrangement. The options in the other Split Territory Programs and the Spinal Muscular Atrophy Program do not provide a material right to the customer that it would receive without entering into the contract principally because the option fees are at least equal to the standalone selling price for the underlying goods. Therefore, the other Split Territory Programs and the Spinal Muscular Atrophy Program options are not performance obligations at inception. The Company has identified $74.6 million of total transaction price consisting of the $65.0 million upfront fee, the $5.0 million premium paid in excess of fair value of the Series B Preferred Stock and $4.6 million of Sanofi Genzyme “in‑kind” funding, which represents the transaction price at inception. Additional consideration to be paid to the Company upon the exercise of the license options by Sanofi Genzyme or upon reaching certain milestones are excluded from the transaction price as they relate to option fees and milestones that can only be achieved subsequent to the option exercise or are outside of the initial contract term. The Company has allocated the transaction price to the separate performance obligations based on their relative standalone selling price. For all performance obligations, the Company determined the standalone selling price at contract inception based on each obligation’s estimated standalone selling price (“ESP”). The Company determined the ESP for the service related deliverable for the research and development activities based on internal estimates of the costs to perform the services, including expected internal expenses and expenses with third parties for services and supplies, marked up to include a reasonable profit margin and adjusted for the scope of the potential license. Significant inputs used to determine the total expense of the research and development activities include, the length of time required and the number and costs of various studies that will be performed to complete the applicable POP Study. The ESP for the AJSC and DAC have been estimated based on the costs incurred to participate in the committees, marked up to include a reasonable profit margin. The ESP for the PD Material Right was determined based on the estimated value of the license adjusted for the estimated probability that the option would be exercised by Sanofi Genzyme. Based on the relative standalone selling price allocation, the allocation of the transaction price to the separate performance obligations was as follows: Performance Obligation Amount (in thousands) Research and Development Services for: Huntington’s Program $ 14,228 Parkinson’s Program 6,040 Friedreich’s ataxia Program 14,821 Spinal Muscular Atrophy Program 29,116 Future Program 2,239 Committee Obligations: AJSC 133 DAC 207 PD Material Right 7,855 Total $ 74,639 The Company recognizes the amounts associated with research and development services and committee obligations on a proportional performance basis over the period of service using input-based measurements such as costs incurred to date, to estimate proportion performed, and remeasures its progress towards completion at the end of each reporting period. The amount allocated to the PD Material Right was initially deferred and recognized in full prior to the adoption of ASC 606. During the three months ended March 31, 2019 and 2018, the Company recognized $1.4 million and $0.5 million of revenue, respectively, associated with its collaboration with Sanofi Genzyme related to research and development services and committee obligations performed during the period. As of March 31, 2019, there was $50.0 million of deferred revenue related to the Sanofi Genzyme Collaboration Agreement, which is classified as either current or non-current in the accompanying balance sheet based on the period the services are expected to be delivered. Costs incurred relating to the programs that Sanofi Genzyme has the option to license under the Sanofi Genzyme Collaboration Agreement consist of internal and external research and development costs, which primarily include: salaries and benefits, lab supplies and preclinical research studies. These costs are included in research and development expenses in the Company’s statement of operations during the three months ended March 31, 2019 and 2018. AbbVie Tau Collaboration Agreement Summary of Agreement In February 2018, the Company entered into an exclusive collaboration and option agreement (the “AbbVie Tau Collaboration Agreement”) with AbbVie for the research, development and commercialization of AAV and other virus-based gene therapy products for the treatment of diseases of the central nervous system and other neurodegenerative diseases related to defective or excess aggregation of tau protein in the human brain, including Alzheimer’s disease. Under the AbbVie Tau Collaboration Agreement, the Company and AbbVie have agreed to collaborate on the research and development of specified vectorized antibody compounds comprised of an AAV or other viral capsid and a virus vector genome that encodes one or more antibodies that target and bind to a tau protein. The collaboration is comprised of a research period (the “Research Period”), a development period (the “Development Period”), and an exclusive license option (the “License Option”). The AbbVie Tau Collaboration Agreement included a non-refundable upfront payment of $69.0 million for services during the Research Period. During the Research Period, each party has agreed to identify up to five antibodies for inclusion in the collaboration. Subject to certain conditions and exceptions, the parties will select up to three antibodies (each, a “Research Antibody”) as candidates for creation of research compounds (each, a “Research Compound”), with AbbVie having the right to select two of the three Research Antibodies. The Company is required to use diligent efforts to conduct antibody engineering and other research activities to create Research Compounds and to develop product candidates containing or comprised of such Research Compounds (“Product Candidates”). The Company is solely responsible for its costs and expenses during the Research Period. During a specified portion of the Research Period, AbbVie may exercise one or more of its exclusive development options (each, a “Development Option”) to select up to a total of three Research Compounds (the “Selected Research Compounds”) and their corresponding Product Candidates (the “Selected Product Candidates”) to proceed to the Development Period. Upon AbbVie’s exercise of a Development Option, AbbVie will pay the Company $80.0 million for the first Selected Research Compound and $30.0 million each for up to two additional Selected Research Compounds. During the Development Period, the Company is obligated to use diligent efforts to conduct development activities, including Investigational New Drug application-enabling and Phase 1 clinical trial activities, for the Selected Research Compounds and corresponding Selected Product Candidates. The Company will be solely responsible for the costs and expenses during the Development Period. During a specified portion of the Development Period (the “License Option Period”), AbbVie may exercise its License Option to further develop and commercialize all of the Research Compounds (the “Licensed Compounds”), and corresponding product candidates (the “Licensed Products”). Upon AbbVie’s exercise of its License Option, AbbVie will provide a one-time payment of $75.0 million to the Company, and the Company will grant to AbbVie an exclusive, worldwide license, with the right to sublicense, under certain of the Company’s intellectual property rights to develop and commercialize the Licensed Compounds and the Licensed Products for all human diagnostic, prophylactic and therapeutic uses. In addition, after AbbVie’s exercise of the License Option, the Company has certain obligations to complete any remaining research and development activities that have not been completed for any Research Compounds and Product Candidates. The Company’s research and development activities will be conducted pursuant to the plans agreed to by the parties and overseen by a joint governance committee (“JGC”) as detailed in the AbbVie Tau Collaboration Agreement. Any material amendment to the research or development plans must be mutually agreed to by the Company and AbbVie, which may be through the JGC. Under the AbbVie Tau Collaboration Agreement, AbbVie is required to use commercially reasonable efforts to develop and commercialize at least one Licensed Product in each of the United States, Japan, the United Kingdom, Germany, France, Italy, and Spain. After exercise of the License Option, AbbVie is solely responsible for all development and commercialization activities relating to Licensed Compounds and Licensed Products at its sole cost and expense, subject to the agreed-upon research and development plans. The Company may elect to share in AbbVie’s development costs relating to a Licensed Product on an indication-by-indication basis in exchange for a specified increase in royalties (a “Cost-Sharing Option”). If the Company exercises a Cost-Sharing Option, the Company may either reimburse AbbVie for AbbVie’s applicable development costs or, in the case of certain budget overruns, AbbVie may instead deduct applicable development costs, up to a specified cap, from milestone and royalty payments owed by AbbVie to the Company. Under the AbbVie Tau Collaboration Agreement, the Company is eligible to receive specified development and first-sale milestone payments for each Licensed Compound of up to an aggregate of $550.0 million in the case of an Alzheimer’s disease indication, up to $230.0 million in the case of the first indication other than Alzheimer’s disease and up to $115.0 million for a subsequent non-Alzheimer’s disease indication. Additionally, the Company is eligible to receive tiered, escalating royalties, in a range from a high-single digit to a mid-to-high teen (or, if the Company has exercised its Cost-Sharing Option, low-twenties) percentage of aggregate net sales of Licensed Products on a Licensed Compound by Licensed Compound basis, subject to potential reductions in certain circumstances. For each Licensed Product, AbbVie also has the right to decrease or eliminate its royalty payments on such Licensed Product in exchange for a one-time payment by AbbVie at a fair market value to be negotiated by the parties or determined pursuant to dispute resolution procedures specified in the AbbVie Collaboration Agreement. Unless earlier terminated, the AbbVie Tau Collaboration Agreement will expire on the earliest to occur of the expiration of (i) the Development Option Period, without AbbVie’s exercise of a Development Option; (ii) the License Option Period, without AbbVie’s exercise of its License Option; and (iii) the last-to-expire royalty term with respect to all Licensed Products in all countries. The Company and AbbVie have customary termination rights including the right to terminate for an uncured material breach of the agreement committed by the other party, and AbbVie has the right to terminate for convenience. Accounting Analysis The Company assessed the promised goods and services under the AbbVie Tau Collaboration Agreement, in accordance with ASC 606, and determined that the AbbVie Tau Collaboration Agreement includes the following performance obligations: (i) research services during the Research Period (through the delivery of the final research report) including the identification of the Research Antibodies, conduct of research activities and provision of information to AbbVie to allow AbbVie to determine whether to exercise up to three development options to be rendered (“Research Services”), and (ii) a material right associated with the Development Option on the first Research Compound and associated Product Candidates (“First Development Option Material Right”). The first Development Option provides AbbVie with (i) additional development services on a selected Research Compound and (ii) the ability to exercise the License Option. The Company has concluded the option provides a material right as the consideration paid by AbbVie upon exercise of the first Development Option is less than the amount that the Company would otherwise expect to receive outside the context of the contract. The Company has concluded that the First Development Option Material Right is a separate performance obligation under ASC 606 as AbbVie is provided additional services and a License Option for additional consideration that represents a significant discount from amounts that would otherwise be offered outside the context of the contract. The First Development Option Material Right is distinct from the other performance obligations in the arrangement as it is an option in the contract that is not required for AbbVie to obtain the benefit of the other promised goods or services in the arrangement. The First Development Option Material Right does not include the underlying goods or services that are delivered upon exercise of the option, but rather represents the value to the customer of having the right to obtain development services and the right to the License Option at an advantageous price. The Company received a nonrefundable, upfront payment of $69.0 million as consideration under the AbbVie Collaboration Agreement, which represents the transaction price at inception. Additional consideration to be paid to the Company upon the exercise of the Development and License Options by AbbVie or upon reaching certain milestones are excluded from the transaction price as they relate to option fees and milestones that can only be achieved subsequent to the option exercise or are outside of the initial contact term. The Company has allocated the transaction price to the separate performance obligations based on their relative standalone selling price. The Company determined the standalone selling price at contract inception based on each obligation’s ESP. The Company determined the ESP for the research services obligation based on internal estimates of the costs to perform the services, including expected internal expenses and expenses with third parties for services and supplies, inclusive of a reasonable profit margin. Significant inputs used to determine the total expense of the research services include the length of time required, the internal hours expected to be incurred on the services and the number and costs of various studies that will be performed to complete the Research Plan. The ESP for the First Development Option Material Right was determined based on the fees AbbVie would pay to exercise the Development and License Options, the estimated costs to perform the development services, inclusive of a reasonable profit margin, the estimated value of the License Option using comparable transactions, and the probability that the Development and License Options would be exercised by AbbVie. Based on the relative standalone selling price, the allocation of the transaction price to the separate performance obligations was as follows: Performance Obligation Amount (in thousands) Research Services $ 34,482 First Development Option Material Right 34,518 Total $ 69,000 The Company recognizes the amounts associated with Research Services on a proportional performance basis over the period of service using input-based measurements of total cost of research incurred to estimate proportion performed and remeasures its progress towards completion at the end of each reporting period. The amount allocated to the First Development Option Material Right is recorded as deferred revenue and will be recognized either over the period in which goods and services underlying the option are transferred or upon expiry of the option. During the three months ended March 31, 2019 and 2018, the Company recognized $1.7 million and $0.4 million of revenue, respectively, associated with the AbbVie Tau Collaboration related to research services performed during the period. As of March 31, 2019, there is $60.4 million of deferred revenue related to the AbbVie Tau Collaboration Agreement, which is classified as either current or non-current in the accompanying 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 statement of operations during the three months ended March 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 of $65.0 million for services during the ASN Research Period. During the ASN Research Period, the Company is obligated to conduct research activities directed to constructing one or more virus vectors that encode antibodies designated by AbbVie (the “AbbVie Designated Antibodies”) which initially are to be antibodies provided by AbbVie. The Company is obligated to use diligent efforts to conduct research activities to create research compounds (“ASN Research Compounds”) and to develop product candidates containing or comprised of the ASN Research Compounds (“ASN Product Candidates”). The Company is solely responsible for the costs and expenses during the ASN Research Period. During a specified portion of the ASN Research Period, AbbVie may exercise one or more of its exclusive development options to select up to a total of four ASN Research Compounds and their corresponding ASN Product Candidates to proceed to the ASN Development Period. Upon AbbVie’s exercise of an option to proceed to the ASN Development Period (an “ASN Development Option”), AbbVie will pay the Company $80.0 million for the first ASN Research Compound and $30.0 million each for up to three additional ASN Research Compounds. During the ASN Development Period, the Company is obligated to use diligent efforts to conduct development activities, including IND application-enabling and Phase 1 clinical trial activities, for each selected ASN Research Compound and corresponding selected ASN Product Candidates. The Company is solely responsible for the costs and expenses during the ASN Development Period. During a specified portion of the ASN Development Period, AbbVie may exercise its ASN License Option to further develop and commercialize all of the ASN Research Compounds and corresponding ASN Product Candidates. Upon AbbVie’s exercise of its ASN License Option, the Company has agreed to grant to AbbVie an exclusive, worldwide license, with the right to sublicense, under certain of the Company’s intellectual property rights to develop and commercialize the licensed compounds and the licensed products for all human diagnostic, prophylactic and therapeutic uses. In addition, after AbbVie’s exercise of the ASN License Option, the Company has certain obligations to complete any remaining research and development activities that have not been completed for any ASN Research Compounds and ASN Product Candidates. The Company’s research and development activities are to be conducted pursuant to the plans agreed to by the parties and overseen by a joint governance committee (or “ASN JGC”) as detailed in the AbbVie Alpha-Synuclein Collaboration Agreement. Any material amendment to the research or development plans, however, must be mutually agreed to by the parties, which may be through the ASN JGC. Under the AbbVie Alpha-Synuclein Collaboration Agreement, AbbVie is required to use commercially reasonable efforts to develop and commercialize at least one licensed product in each of the United States, Japan, the United Kingdom, Germany, France, Italy and Spain. After exercise of the ASN License Option, AbbVie is solely responsible for all development and commercialization activities relating to licensed compounds and licensed products at its sole cost and expense, subject to the Company’s obligation to complete any remaining research and development activities set forth in the agreed-upon research and development plans. Under the terms of the AbbVie Alpha-Synuclein Collaboration Agreement, the Company is eligible to receive (i) specified development and first-sale milestone payments for each licensed compound of up to an aggregate of $450.0 million in the case of a Parkinson’s disease indication and up to $185.0 million in the case of the first indication other than Parkinson’s disease and $92.5 million for a subsequent non-Parkinson’s disease indication; (ii) specified commercial milestone payments based on net sales for all licensed products and all indications up to an aggregate of $500.0 million; and (iii) tiered, escalating royalties, in the mid-single digit percentage range for aggregate net sales of licensed products on a licensed compound by licensed compound basis, subject to potential reductions in certain circumstances. Unless earlier terminated, the AbbVie Alpha-Synuclein Collaboration Agreement expires on the earliest to occur of the expiration of (i) the ASN Development Period, without AbbVie’s exercise of an ASN Development Option; (ii) the license option period, without AbbVie’s exercise of its ASN License Option; and (iii) the last-to-expire royalty term with respect to all licensed products in all countries. The Company and AbbVie have customary termination rights including the right to terminate for an uncured material breach of the agreement committed by the other party, and AbbVie has the right to terminate for convenience. Upon termination in certain cases, the vectorized antibody exclusivity and AbbVie designated exclusivity survives until the third anniversary of the termination date. If the parties mutually agree to terminate for infeasibility or AbbVie terminates for the Company’s failure to deliver a final research or development report, neither the Company nor any of its affiliates may directly or indirectly exploit a vectorized antibody compound that targets or binds to the alpha-synuclein protein for 18 months after the termination date. Accounting Analysis The Company assessed the promised goods and services under the AbbVie Alpha-Synuclein Collaboration Agreement, in accordance with ASC 606, and determined that the AbbVie Alpha-Synuclein Collaboration Agreement includes the

Preferred stock

Preferred stock	3 Months Ended
	Mar. 31, 2019
Preferred stock
Preferred stock	8. Preferred stock The Company has authorized preferred stock amounting to 5,000,000 shares as of March 31, 2019 and December 31, 2018. The authorized preferred stock was classified under stockholders’ equity at March 31, 2019 and December 31, 2018.

Stock based compensation

Stock based compensation	3 Months Ended
	Mar. 31, 2019
Stock based compensation
Stock based compensation	9. Stock‑based compensation 2014 Stock Option and Grant Plan In January 2014, the Company adopted the 2014 Stock Option and Grant Plan (the “2014 Plan”), under which it could grant incentive stock options, non‑qualified stock options, restricted stock awards, unrestricted stock awards, or restricted stock units to purchase up to 823,529 shares of common stock to employees, officers, directors and consultants of the Company. In April 2014, the Company amended the 2014 Plan to allow for the issuance of up to 1,411,764 shares of common stock. In August 2014, April 2015, August 2015, and October 2015, the Company further amended the 2014 Plan to allow for the issuance of up to 2,000,000, 2,047,058, 2,669,411, and 2,998,823 shares of common stock, respectively. During 2014 the Company issued only restricted stock awards under the 2014 Plan and during 2015 the Company only granted stock options under the 2014 Plan. The terms of stock option agreements, including vesting requirements, were determined by the Board of Directors and were subject to the provisions of the 2014 Plan. Restricted stock awards granted by the Company generally vest based on each grantee’s continued service with the Company during a specified period following grant. Stock options granted to employees generally vest over four years, with 25% vesting on the one year anniversary and 75% vesting ratably, on a monthly basis, over the remaining three years. Stock options granted to non‑employee consultants generally vest monthly over a period of one to four years. Founder Awards In January 2014, the Company issued 1,188,233 shares of restricted stock to its founders at an original issuance price of $0.0425 per share. Of the total restricted shares awarded to the founders, 835,292 shares generally vested over one to four years, based on each founder’s continued service to the Company in varying capacity as a Scientific Advisory Board member, consultant, director, officer or employee, as set forth in each grantee’s individual restricted stock purchase agreement. These shares were fully vested as of March 31, 2019. Stock-based compensation expense associated with these time-based awards was recognized over the vesting period. The remaining 352,941 of the shares issued begin vesting upon the achievement of certain performance objectives as well as continued service to the Company, as set forth in the agreements. These performance conditions are tied to certain milestone events specific to the Company’s corporate goals, including but not limited to preclinical and clinical development milestones related to the Company’s product candidates. Stock‑based compensation expense associated with these performance‑based awards is recognized when the achievement of the performance condition is considered probable, using management’s best estimates. During 2016, management determined that the achievement of the performance milestone for one of the three performance‑based awards had become probable. Accordingly, stock-based compensation expense was recorded related to this award in the amount of $0.2 million and $1.5 million, during the three months ended and term to date ended March 31, 2018. No stock‑based compensation expense was recorded in 2019 related to this award as it was fully vested during 2018. No stock‑based compensation expense was recorded for the remaining two founders’ awards with performance-based vesting as of March 31, 2019 as the performance-based milestones related to these awards were not considered probable of being achieved. 2015 Stock Option Plan In October 2015, the Company’s board of directors and stockholders approved the 2015 Stock Option and Incentive Plan (the “2015 Stock Option Plan”), which became effective upon the completion of the Company’s initial public offering (the “IPO”). The 2015 Stock Option Plan provides the Company with the flexibility to use various equity-based incentive and other awards as compensation tools to motivate its workforce. These tools include stock options, stock appreciation rights, restricted stock, restricted stock units, unrestricted stock, performance share awards and cash-based awards. The 2015 Stock Option Plan replaced the 2014 Plan. Any options or awards outstanding under the 2014 Plan remained outstanding and effective. The number of shares initially reserved for issuance under the 2015 Stock Option Plan is the sum of (i) 1,311,812 shares of common stock and (ii) the number of shares under the 2014 Plan that are not needed to fulfill the Company’s obligations for awards issued under the 2014 Plan as a result of forfeiture, expiration, cancellation, termination or net issuances of awards thereunder. The number of shares of common stock that may be issued under the 2015 Stock Option Plan is also subject to increase on the first day of each fiscal year by up to 4% of the Company’s issued and outstanding shares of common stock on the immediately preceding December 31. Effective January 1, 2016, 2017, 2018, and 2019 an additional 1,069,971, 1,070,635, 1,285,200, and 1,302,830 shares, respectively, were added to the Company’s 2015 Stock Option Plan for future issuance. As of March 31, 2019, there were 2,275,140 shares of common stock available for future issuance under the 2015 Stock Option Plan. During the three months ended March 31, 2019, the Company granted both stock options and restricted stock units to employees under the 2015 Stock Option Plan. The Company issued 753,340 stock options and 354,405 restricted stock units to employees during the three months ended March 31, 2019. There were no new equity awards to non-employees under the 2015 Stock Option Plan during the three months ended March 31, 2019. 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. The number of shares of common stock that may be issued under the 2015 ESPP is also subject to increase on the first day of each fiscal year by up to 1% of the Company’s issued and outstanding shares of common stock on the immediately preceding December 31. Effective January 1, 2016, 2017, 2018, and 2019, 267,492, 267,658, 321,300, and 325,707 shares of common stock, respectively, were added to the 2015 ESPP. 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: Three Months Ended March 31, 2019 2018 (in thousands) Research and development $ 1,416 $ 1,198 General and administrative 2,102 1,124 Total stock-based compensation expense $ 3,518 $ 2,322 Stock-based compensation expense by type of award included within the consolidated statements of operations and comprehensive loss was as follows: Three Months Ended March 31, 2019 2018 (in thousands) Stock options $ 2,776 $ 1,966 Restricted stock awards and units 683 294 Employee stock purchase plan awards 59 62 Total stock-based compensation expense $ 3,518 $ 2,322 Restricted Stock Units A summary of the status of and changes in unvested restricted stock unit activity under the Company’s equity award plan for the three months ended March 31, 2018 was as follows: Weighted Average Grant Date Fair Value Units Per Unit Unvested restricted stock units as of December 31, 2018 — — Granted 354,405 $ 9.10 Vested — — Forfeited (2,790) $ 9.10 Unvested restricted stock units as of March 31, 2019 351,615 $ 9.10 Stock-based compensation of restricted stock units is based on the fair value of the Company’s common stock on the date of grant and recognized over the vesting period. The weighted average fair value of restricted stock units granted to employees during the three months ended March 31, 2019 was $9.10 per share. The restricted stock units granted in the three months ended March 31, 2019 vest in equal amounts, annually over three years. There were no restricted stock units granted to employees in the three months ended March 31, 2018. The expense related to restricted stock units granted to employees was $0.7 million for the three months ended March 31, 2019. As of March 31, 2019, the Company had unrecognized stock-based compensation expense related to its unvested restricted stock units of $2.5 million, which is expected to be recognized over the remaining average vesting period of 2.8 years. Stock Options The following is a summary of stock option activity for the three months ended March 31, 2019: Weighted Remaining Aggregate Average Contractual Intrinsic Exercise Life Value Shares Price (in years) (in thousands) Outstanding at December 31, 2018 4,225,152 $ 15.91 Granted 753,340 $ 9.32 Exercised (31,360) $ 9.05 Cancelled or forfeited (104,038) $ 12.93 Outstanding at March 31, 2019 4,843,094 $ 14.99 8.5 $ 25,251 Exercisable at March 31, 2019 1,674,666 $ 13.07 7.5 11,684 Vested and expected to vest at March 31, 2019 4,843,094 $ 14.99 8.5 $ 25,251 Using the Black ‑ Scholes option pricing model, the weighted-average fair value of options granted to employees and directors during the three months ended March 31, 2019 was $6.23 per share. The expense related to awards granted to employees and directors was $2.8 million for the three months ended March 31, 2019. The weighted-average fair value of options granted to employees and directors during the three months ended March 31, 2018 was $16.49 per share. The expense related to awards granted to employees and directors was $1.9 million for the three months ended March 31, 2018. The fair value of each option issued to employees and directors was estimated at the date of grant using the Black‑Scholes option pricing model with the following weighted‑average assumptions: Three Months Ended March 31, 2019 2018 Risk-free interest rate 2.5 % 2.7 % Expected dividend yield — % — % Expected term (in years) 6.0 6.0 Expected volatility 75.0 % 74.3 % There were no new equity awards granted to non ‑ employees during the three months ended March 31, 2019 and 2018. The expense related to awards granted to non ‑ employees was $32.0 thousand and $0.1 million for the three months ended March 31, 2019 and 2018, respectively. As of March 31, 2019, the Company had unrecognized stock-based compensation expense related to its unvested stock options of $27.5 million which is expected to be recognized over the remaining weighted-average vesting period of 2.8 years .

Income taxes

Income taxes	3 Months Ended
	Mar. 31, 2019
Income taxes
Income taxes	10. Income taxes Deferred tax assets and deferred tax liabilities are recognized based on temporary differences between the financial reporting and tax basis of assets and liabilities using statutory rates. A valuation allowance is recorded against deferred tax assets if it is more likely than not that some or all of the deferred tax assets will not be realized. Due to the uncertainty surrounding the realization of the favorable tax attributes in future tax returns, the Company has recorded a full valuation allowance against the Company’s otherwise recognizable net deferred tax assets. For the three months ended March 31, 2019 and 2018, the Company recognized a de minimis tax expense in other comprehensive income related to the unrealized gain on available-for-sale securities.

Net loss per share

Net loss per share	3 Months Ended
	Mar. 31, 2019
Net loss per share
Net loss per share	11. 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 so include them would be anti-dilutive: As of March 31, 2019 2018 Unvested restricted common stock awards 235,294 412,150 Unvested restricted common stock units 351,615 — Outstanding stock options 4,843,094 6,810,806 Total 5,430,003 7,222,956

Related party transactions

Related party transactions	3 Months Ended
	Mar. 31, 2019
Related party transactions
Related party transactions	12. Related‑party transactions Historically, the Company has received consulting and management services from one of its investors. During the three months ended March 31, 2019 and 2018, there were no consulting and management services provided by this investor, and as of March 31, 2019, there were no amounts payable related to consulting and management service fees provided by this investor.

Summary of significant accoun_2

Summary of significant accounting policies (Policies)	3 Months Ended
	Mar. 31, 2019
Summary of significant accounting policies
Basis of presentation	Basis of presentation The accompanying unaudited condensed consolidated financial statements of the Company have been prepared in accordance with accounting principles generally accepted in the United States (“GAAP”) for interim financial reporting and as required by Regulation S-X, Rule 10-01. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. For further information, refer to the consolidated financial statements and footnotes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018 as filed with the Securities and Exchange Commission (“SEC”) on February 26, 2019. These interim condensed consolidated financial statements, in the opinion of management, reflect all normal recurring adjustments necessary for a fair presentation of the Company’s financial position and results of operations for the periods presented. Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASU”) of the Financial Accounting Standards Board (“FASB”). See “ Recently Adopted Accounting Pronouncements ” below for discussion of the Company’s adoption of new guidance effective January 1, 2019. All amounts and disclosures set forth in this Quarterly Report on Form 10-Q reflect adoption of these changes.
Principles of consolidation	Principles of consolidation The unaudited interim consolidated financial statements include the accounts of the Company and its wholly owned subsidiary as disclosed in Note 2, Summary of Significant Accounting Policies, within the “Notes to Consolidated Financial Statements” accompanying the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2018. Intercompany accounts and transactions have been eliminated.
Use of estimates	Use of estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. On an ongoing basis, the Company’s management evaluates its estimates, which include, but are not limited to, estimates related to revenue recognition, accrued expenses, stock-based compensation expense, and income taxes. The Company bases its estimates on historical experience and other market specific or other relevant assumptions that it believes to be reasonable under the circumstances. Actual results may differ from those estimates or assumptions. Certain reclassifications have been made to prior periods to conform to current period presentation.
Leases	Leases Effective January 1, 2019, the Company accounted for its operating leases in accordance with ASC Topic 842 Leases (“ASC 842”). ASC 842 provides guidance on accounting for lease arrangements by both lessors and lessees and requires lessees to recognize a lease liability and a right-of-use asset for most leases. The Company determines if an arrangement is a lease at inception. The Company’s operating leases are included in operating lease right-of-use (“ROU”) assets, other current liabilities, and other non-current liabilities on the consolidated balance sheets. ROU assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating lease ROU assets and liabilities are recognized at adoption date based on the present value of lease payments over the lease term. As the Company’s leases do not provide an implicit rate, an incremental borrowing rate was used based on the information available at the lease commencement date in determining the present value of lease payments. On future lease obligations, the implicit rate will be set when readily determinable. The operating lease ROU assets also include the effect of any lease payments made and exclude lease incentives. The Company’s lease terms may include options to extend or terminate the lease even when it is not reasonably certain that the option will be exercised. Lease expense for lease payments is recognized on a straight-line basis over the lease term. The Company has lease agreements with lease and non-lease components, which are accounted for separately. Non-lease components generally refer to common area maintenance charges related to the premises.
Revenue recognition	Revenue recognition The Company enters into collaboration agreements which are within the scope of ASC 606, Revenue from Contracts with Customers (“ASC 606”), under which the Company licenses rights to certain of the Company’s product candidates and performs research and development services. The terms of these arrangements typically include payment of one or more of the following: non-refundable, upfront fees; reimbursement of research and development costs; development, regulatory, and commercial milestone payments; and royalties on net sales of licensed products. Under ASC 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine the appropriate amount of revenue to be recognized for arrangements determined to be within the scope of ASC 606, the Company performs the following five steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect consideration it is entitled to in exchange for the goods or services it transfers to the customer. The promised goods or services in 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.
Stock-based compensation expense	Stock‑based compensation expense The Company accounts for its stock‑based compensation awards in accordance with ASC Topic 718 Compensation—Stock Compensation (“ASC 718”). ASC 718 requires all stock‑based payments to employees, nonemployees, and directors, including grants of restricted stock units and stock options, to be recognized as expense in the statements of operations based on their grant date fair values. The Company estimates the fair value of options granted using the Black‑Scholes option pricing model. The Company uses the fair value of its common stock on the grant date to determine the fair value of restricted stock units. The Black‑Scholes option pricing model requires inputs based on certain subjective assumptions, including (a) the expected stock price volatility, (b) the calculation of expected term of the award, (c) the risk‑free interest rate and (d) expected dividends. Due to a lack of company-specific historical and implied volatility data, the Company bases the estimate of expected volatility on the historical volatility of a group of similar companies that are publicly traded, blended with the most recent period of historic volatility of its common stock. The historical volatility is calculated based on a period of time commensurate with the expected term assumption. The computation of expected volatility is based on the historical volatility of a representative group of companies with similar characteristics to the Company, including stage of product development and life science industry focus. The Company uses the simplified method as prescribed by the SEC Staff Accounting Bulletin No. 107, Share‑Based Payment , to calculate the expected term for stock options granted to employees as it does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term. For stock options granted to non‑employees, the Company utilizes the contractual term of the arrangement as the basis for the expected term assumption. The risk‑free interest rate is based on a treasury instrument whose term is consistent with the expected term of the stock options. The expected dividend yield is assumed to be zero as the Company has never paid dividends and has no current plans to pay any dividends on its common stock. The Company expenses the fair value of its stock‑based compensation awards on a straight‑line basis over the associated service period, which is generally the period in which the related services are received. The Company records the expense for stock‑based compensation awards subject to performance conditions over the remaining service period when management determines that achievement of the performance condition is probable. Management evaluates if the achievement of a performance condition is probable based on the expected satisfaction of the performance conditions as of the reporting date.
Recent accounting pronouncements	Recently Adopted Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, a comprehensive new lease accounting standard, which provides revised guidance on accounting for lease arrangements by both lessors and lessees and requires lessees to recognize a lease liability and a right-of-use asset for most leases. In July 2018, the FASB issued ASU No. 2018-11, Leases (“ASC 842”), Targeted Improvements , which provides an additional transition method that allowed entities to initially apply the new lease requirements at the adoption date, not the earliest period presented, and recognize a cumulative effect adjustment to the opening balance of retained earnings in the period of adoption. The Company elected this transition method at the adoption date of January 1, 2019. The Company elected a package of practical expedients, under which an entity need not reassess whether any expired or existing contracts are or contain leases, the lease classification for any expired or existing leases, or initial direct costs for any existing leases. The impact of adopting ASC 842 was represented as a capitalization of a right-of-use asset of approximately $31.0 million with a corresponding lease liability of approximately $36.7 million to be recognized over the remaining life of the Company’s leases. In June 2018, the FASB issued ASU No. 2018-07, Compensation-Stock Compensation: Improvements to Nonemployee Share-Based Payment Accounting (“ASC 718”). 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 this ASC on January 1, 2019 did not have a material impact on the Company's consolidated financial statements. Recent Accounting Pronouncements In August 2018, the FASB issued ASU No. 2018-13, Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement (“ASU 2018-13”). This standard eliminates, adds and modifies certain disclosure requirements for fair value measurements as part of its disclosure framework project. ASU 2018-13 is effective for annual reporting periods beginning after December 15, 2019 and interim periods within those annual periods and early adoption is permitted. The Company is currently evaluating the potential impact that this guidance may have on its consolidated financial statements. In June 2016, the FASB issued ASU No. 2016-13, Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”). ASU 2016-13 will change how companies account for credit losses for most financial assets and certain other instruments. For trade receivables, loans and held-to-maturity debt securities, companies will be required to recognize an allowance for credit losses rather than reducing the carrying value of the asset. ASU 2016-13 is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted. The Company is currently evaluating the potential impact that this guidance may have on its consolidated financial statements.

Fair value measurements (Tables

Fair value measurements (Tables)	3 Months Ended
	Mar. 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 March 31, 2019 and December 31, 2018 are as follows: Quoted Prices Significant in Active Other Significant Markets for Observable Unobservable Identical Assets Inputs Inputs Assets Total (Level 1) (Level 2) (Level 3) March 31, 2019 (in thousands) Money market funds included in cash and cash equivalents $ 112,872 $ 112,872 $ — $ — Marketable securities: U.S. Treasury notes 245,238 245,238 — — Equity securities 1,280 1,280 — — Total marketable securities $ 246,518 $ 246,518 $ — $ — Warrants to purchase equity securities 547 — 547 — Total $ 359,937 $ 359,390 $ 547 $ — 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 $ —
Summary of fair value assumptions	The assumptions utilized to value the warrants to purchase equity securities as of March 31, 2019 and December 31, 2018 are as follows: As of March 31, As of December 31, 2019 2018 Risk-free interest rate 2.2 % 2.5 % Expected dividend yield — % — % Expected term (in years) 2.4 2.7 Expected volatility 103.7 % 112.7 %

Cash, cash equivalents, restr_2

Cash, cash equivalents, restricted cash, and available for sale marketable securities (Tables)	3 Months Ended
	Mar. 31, 2019
Cash, cash equivalents, restricted cash, and available for sale marketable securities
Cash, cash equivalents and marketable securities	Cash, cash equivalents, and marketable securities included the following at March 31, 2019 and December 31, 2018: Amortized Unrealized Unrealized Fair Cost Gains Losses Value (in thousands) As of March 31, 2019 Money market funds included in cash and cash equivalents $ 112,872 $ — $ — $ 112,872 Marketable securities: U.S. Treasury notes 245,186 52 — 245,238 Equity securities 1,220 60 — 1,280 Total marketable securities $ 246,406 $ 112 $ — $ 246,518 Total money market funds and marketable securities $ 359,278 $ 112 $ — $ 359,390 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 March 31, 2019 2018 (in thousands) Cash and cash equivalents $ 113,261 $ 140,371 Restricted cash included in deposits and other non-current assets 735 735 Total cash, cash equivalents, and restricted cash $ 113,996 $ 141,106

Accrued expenses (Tables)

Accrued expenses (Tables)	3 Months Ended
	Mar. 31, 2019
Accrued expenses
Schedule of accrued expenses	Accrued expenses as of March 31, 2019 and December 31, 2018 consist of the following: As of March 31, As of December 31, 2019 2018 (in thousands) Research and development costs $ 4,922 $ 3,555 Employee compensation costs 1,904 3,780 Professional services 1,445 1,448 Accrued goods and services 879 784 Patent costs 70 120 Other 56 101 Total $ 9,276 $ 9,788

Right-of-use asset and lease _2

Right-of-use asset and lease liabilities (Tables)	3 Months Ended
	Mar. 31, 2019
Right-of-use asset and lease liabilities
Summary of total minimum lease payments	Total Minimum Lease Payments (in thousands) 2019 (remainder of year) $ 4,134 2020 5,960 2021 6,138 2022 6,323 2023 6,512 2024+ 20,897 $ 49,964

Commitments and contingencies (

Commitments and contingencies (Tables)	3 Months Ended
	Mar. 31, 2019
Sanofi Genzyme Collaboration Agreement
Schedule of allocation of transaction price	Performance Obligation Amount (in thousands) Research and Development Services for: Huntington’s Program $ 14,228 Parkinson’s Program 6,040 Friedreich’s ataxia Program 14,821 Spinal Muscular Atrophy Program 29,116 Future Program 2,239 Committee Obligations: AJSC 133 DAC 207 PD Material Right 7,855 Total $ 74,639
AbbVie Tau Collaboration Agreement
Schedule of allocation of transaction price	Performance Obligation Amount (in thousands) Research Services $ 34,482 First Development Option Material Right 34,518 Total $ 69,000
AbbVie Alpha Synuclein Collaboration Agreement
Schedule of allocation of transaction price	Performance Obligation Amount (in thousands) ASN Research Services $ 23,768 ASN First Development Option Material Right 41,232 Total $ 65,000
Neurocrine Collaboration Agreement
Schedule of allocation of variable consideration	Performance Obligation Amount (in thousands) Variable Consideration AADC Program $ 170,418 FA Program 114,023 Discovery Program 1 73,416 Discovery Program 2 73,416 Total $ 431,273
Schedule of allocation of fixed consideration	Performance Obligation Amount (in thousands) Fixed Consideration AADC Program $ 76,023 FA Program 5,680 Discovery Program 1 2,840 Discovery Program 2 2,840 Total $ 87,383

Stock based compensation (Table

Stock based compensation (Tables)	3 Months Ended
	Mar. 31, 2019
Stock based compensation
Compensation cost recognized for all stock-based compensation awards	Total compensation cost recognized for all stock‑based compensation awards in the statements of operations and comprehensive loss is as follows: Three Months Ended March 31, 2019 2018 (in thousands) Research and development $ 1,416 $ 1,198 General and administrative 2,102 1,124 Total stock-based compensation expense $ 3,518 $ 2,322
Summary of stock-based compensation expense by classification	Three Months Ended March 31, 2019 2018 (in thousands) Stock options $ 2,776 $ 1,966 Restricted stock awards and units 683 294 Employee stock purchase plan awards 59 62 Total stock-based compensation expense $ 3,518 $ 2,322
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 — — Granted 354,405 $ 9.10 Vested — — Forfeited (2,790) $ 9.10 Unvested restricted stock units as of March 31, 2019 351,615 $ 9.10
Summary of status and changes in stock options	The following is a summary of stock option activity for the three months ended March 31, 2019: Weighted Remaining Aggregate Average Contractual Intrinsic Exercise Life Value Shares Price (in years) (in thousands) Outstanding at December 31, 2018 4,225,152 $ 15.91 Granted 753,340 $ 9.32 Exercised (31,360) $ 9.05 Cancelled or forfeited (104,038) $ 12.93 Outstanding at March 31, 2019 4,843,094 $ 14.99 8.5 $ 25,251 Exercisable at March 31, 2019 1,674,666 $ 13.07 7.5 11,684 Vested and expected to vest at March 31, 2019 4,843,094 $ 14.99 8.5 $ 25,251
Assumptions	The fair value of each option issued to employees and directors was estimated at the date of grant using the Black‑Scholes option pricing model with the following weighted‑average assumptions: Three Months Ended March 31, 2019 2018 Risk-free interest rate 2.5 % 2.7 % Expected dividend yield — % — % Expected term (in years) 6.0 6.0 Expected volatility 75.0 % 74.3 %

Net loss per share (Tables)

Net loss per share (Tables)	3 Months Ended
	Mar. 31, 2019
Net loss per share
Outstanding potentially dilutive securities excluded in the calculation of diluted net loss per share	As of March 31, 2019 2018 Unvested restricted common stock awards 235,294 412,150 Unvested restricted common stock units 351,615 — Outstanding stock options 4,843,094 6,810,806 Total 5,430,003 7,222,956

Nature of business (Details)

Nature of business (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Nature of business
Accumulated deficit	$ (296,221)	$ (269,051)
Proceeds raised	635,000
Cash, cash equivalents, and marketable debt securities	$ 358,500

Summary of significant accoun_3

Summary of significant accounting policies - ASU (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stock-based compensation, fair value assumptions, expected dividend rate	0.00%
Operating lease, right-of-use asset	$ 30,294
ASU 2016-02 | Restatement Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, right-of-use asset		$ 31,000
Operating lease liability		$ 36,700

Fair value measurements - Asset

Fair value measurements - Assets measured on a recurring basis - (Details) $ in Thousands	Mar. 31, 2019USD ($)item	Dec. 31, 2018USD ($)item	Mar. 31, 2018USD ($)
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	$ 113,261	$ 46,859	$ 140,371
Measurement Input, Risk-Free Interest Rate
Fair value assumptions
Warrants, measurement input	0.022	0.025
Measurement Input, Expected Term
Fair value assumptions
Warrants, measurement input | item	0.024	0.027
Measurement Input, Expected Volatility
Fair value assumptions
Warrants, measurement input | item	1.037	1.127
Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Marketable securities	$ 246,518	$ 109,575
Total assets measured at fair value	359,937	155,982
Level 1 | Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Marketable securities	246,518	109,575
Total assets measured at fair value	359,390	155,748
Level 2 | Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Total assets measured at fair value	547	234
U.S. Treasury notes | Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Marketable securities	245,238	108,947
U.S. Treasury notes | Level 1 | Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Marketable securities	245,238	108,947
Equity securities | Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Marketable securities	1,280	628
Equity securities | Level 1 | Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Marketable securities	1,280	628
Warrants to purchase equity securities | Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Warrants to purchase equity securities	547	234
Warrants to purchase equity securities | Level 2 | Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Warrants to purchase equity securities	547	234
Money market funds
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	112,872	46,173
Money market funds | Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	112,872	46,173
Money market funds | Level 1 | Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	$ 112,872	$ 46,173

Cash, cash equivalents, restr_3

Cash, cash equivalents, restricted cash, and available for sale marketable securities (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Amortized Cost
Cash and cash equivalents	$ 113,261,000	$ 46,859,000	$ 140,371,000
Total marketable securities, amortized cost	246,406,000	110,171,000
Total money market funds and marketable securities	359,278,000	156,344,000
Fair Value
Total marketable securities	246,518,000	109,575,000
Total money market funds and marketable securities	359,390,000	155,748,000
Unrealized Gains and Losses
Total marketable securities, unrealized gains	112,000	1,000
Total money market funds and marketable securities	$ 112,000	1,000
Total marketable securities, unrealized losses		597,000
Total money market funds and marketable securities		$ 597,000
Debt securities, contractual maturity period	1 year	1 year
Other than temporary losses	$ 0
Money market funds
Amortized Cost
Cash and cash equivalents	112,872,000	$ 46,173,000
U.S. Treasury notes
Amortized Cost
Marketable securities, amortized cost	245,186,000	108,951,000
Fair Value
Marketable debt securities, fair value	245,238,000	108,947,000
Unrealized Gains and Losses
Marketable securities, unrealized gains	52,000	1,000
Marketable securities, unrealized losses		5,000
Equity securities
Amortized Cost
Marketable equity securities, amortized cost	1,220,000	1,220,000
Fair Value
Marketable equity securities, fair value	1,280,000	628,000
Unrealized Gains and Losses
Equity securitiess, unrealized gains	$ 60,000
Equity securitiess, unrealized losses		$ 592,000

Cash, cash equivalents, restr_4

Cash, cash equivalents, restricted cash, and available for sale marketable securities - Restricted cash (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Cash, cash equivalents, restricted cash, and available for sale marketable securities
Cash and cash equivalents	$ 113,261	$ 46,859	$ 140,371
Restricted cash included in deposits and other non-current assets	735		735
Total cash, cash equivalents, and restricted cash	$ 113,996	$ 47,594	$ 141,106	$ 32,265

Accrued expenses (Details)

Accrued expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accrued expenses
Research and development costs	$ 4,922	$ 3,555
Employee compensation costs	1,904	3,780
Professional services	1,445	1,448
Accrued goods and services	879	784
Patent costs	70	120
Other	56	101
Total	$ 9,276	$ 9,788

Right-of-use asset and lease _3

Right-of-use asset and lease liabilities (Details) $ in Thousands	1 Months Ended	3 Months Ended
	Apr. 30, 2014item	Mar. 31, 2019USD ($)	Mar. 31, 2018USD ($)
Lease, Practical Expedients, Package [true false]		true
Lessee, Operating Lease, Existence of Option to Extend [true false]		true
Rent expense		$ 1,400	$ 800
Restricted cash included in deposits and other non-current assets		$ 735	$ 735
Weighted average remaining lease term		7 years 8 months 12 days
Weighted average incremental borrowing rate		8.5
Total minimum lease payments
2019 (remainder)		$ 4,134
2020		5,960
2021		6,138
2022		6,323
2023		6,512
2024+		20,897
Total		49,964
75 Sidney Street
Number of renewal options | item	2
Term of each renewal option	5 years
Leasehold improvements		1,300
Entitled leasehold improvements		300
64 Sidney Street
Leasehold improvements		$ 3,500

Commitments and contingencies -

Commitments and contingencies - Significant Agreements - (Details) $ in Millions	1 Months Ended
	Feb. 28, 2015USD ($)shares
Sanofi Genzyme
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Non-refundable upfront payment received	$ 65
Amount of reduction in milestone or royalty payments to be made by collaborative partner for each program specified	10
Collaborative Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Per Milestone, maximum milestone payments to be received from collaborative partner	540
Collaborative Arrangement | Sanofi Genzyme
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Non-refundable upfront payment received	65
Collaborative Arrangement | Regulatory approval milestone
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Aggregate maximum milestone payments to be received from collaborative partner	220
Collaborative Arrangement | Regulatory approval milestone | Minimum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Per Milestone, maximum milestone payments to be received from collaborative partner	40
Collaborative Arrangement | Regulatory approval milestone | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Per Milestone, maximum milestone payments to be received from collaborative partner	50
Collaborative Arrangement | Commercial Milestone
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Aggregate maximum milestone payments to be received from collaborative partner	320
Collaborative Arrangement | Commercial Milestone | Minimum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Per Milestone, maximum milestone payments to be received from collaborative partner	50
Collaborative Arrangement | Commercial Milestone | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Per Milestone, maximum milestone payments to be received from collaborative partner	100
Parkinson's Program | Regulatory and commercial milestone
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments no longer receivable	105
Spinal Muscular Atrophy Program | Sanofi Genzyme
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Maximum potential in-kind services to be provided by collaborative partner	5
Option exercise payment required from collaborative partner for each program specified	30
Split Territory Program | Sanofi Genzyme
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Option exercise payment required from collaborative partner for each program specified	20
Redeemable Convertible Preferred Stock Series B | Sanofi Genzyme
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Non-refundable upfront payment received	$ 30
Temporary equity issued (in shares) | shares	10,000,000
Fair value of temporary equity issued	$ 25
Premium over fair value on temporary equity issued	5
Redeemable Convertible Preferred Stock Series B | Collaborative Arrangement | Sanofi Genzyme
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Premium over fair value on temporary equity issued	$ 5

Commitments and contingencies_2

Commitments and contingencies - Accounting Analysis - (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Feb. 28, 2015	Mar. 31, 2019	Mar. 31, 2018
Allocable arrangement consideration allocation
Committee Obligations: Alliance Joint Steering Committee ("AJSC")	$ 133
Committee Obligations: Development Advisory Committee ("DAC")	207
PD Material Right	7,855
Total allocable arrangement consideration allocations.	74,639
Huntington's Program
Allocable arrangement consideration allocation
Research and development services	14,228
Parkinson's Program
Allocable arrangement consideration allocation
Research and development services	6,040
Friedreich's ataxia Program
Allocable arrangement consideration allocation
Research and development services	14,821
Spinal Muscular Atrophy Program
Allocable arrangement consideration allocation
Research and development services	29,116
Future Program
Allocable arrangement consideration allocation
Research and development services	2,239
Sanofi Genzyme
Allocable arrangement consideration
Collaborative Arrangement Nonredeemable Up Front Fee Received	65,000
Sanofi Genzyme | Collaborative Arrangement
Allocable arrangement consideration
Collaborative Arrangement Nonredeemable Up Front Fee Received	65,000
In-kind services and other funding to be provided by collaborative partner	4,600
Total allocable arrangement consideration	74,600
Income Statement Related Disclosures [Abstract]
Revenue recognized		$ 1,400	$ 500
Deferred revenue		$ 50,000
Redeemable Convertible Preferred Stock Series B | Sanofi Genzyme
Allocable arrangement consideration
Collaborative Arrangement Nonredeemable Up Front Fee Received	30,000
Additional consideration, premium over fair value on temporary equity issued	5,000
Redeemable Convertible Preferred Stock Series B | Sanofi Genzyme | Collaborative Arrangement
Allocable arrangement consideration
Additional consideration, premium over fair value on temporary equity issued	$ 5,000

Commitments and contingencies_3

Commitments and contingencies - AbbVie Tau Collaboration Agreement - (Details) $ in Millions	1 Months Ended		3 Months Ended
	Feb. 28, 2018USD ($)item	Feb. 28, 2015USD ($)	Mar. 31, 2019USD ($)item	Mar. 31, 2018USD ($)
Sanofi Genzyme
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Non-refundable upfront payment received		$ 65
AbbVie Tau Collaboration Agreement | AbbVie
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Non-refundable upfront payment received	$ 69
First Research Compound payment	80
Two additional research compounds payment to be received for each	$ 30
Number of additional research compounds | item	2
One-time payment upon exercise of license option	$ 75
Milestone payments to be received for licensed compound in case Alzheimer disease indication	550
Milestone payments to be received for licensed compound in case first indication other than Alzheimer disease	230
Milestone payments to be received for licensed compound for subsequent non-Alzheimer disease indication	$ 115
Number of development options | item			3
Number of research antibodies | item	1
Deferred revenue			$ 60.4
Revenue recognized			1.7	$ 0.4
Allocation of Transaction Price
Allocation of Transaction Price			69,000
AbbVie Tau Collaboration Agreement | AbbVie | Minimum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Antibodies to include in Research Period | item	2
The number of Licensed Products | item	1
AbbVie Tau Collaboration Agreement | AbbVie | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of antibodies encoded by virus | item	5
Antibodies to include in Research Period | item	3
AbbVie Tau Collaboration Agreement | AbbVie | Research Services
Allocation of Transaction Price
Allocation of Transaction Price			34,482
AbbVie Tau Collaboration Agreement | AbbVie | First Development Option Material Right
Allocation of Transaction Price
Allocation of Transaction Price			$ 34,518

Commitments and contingencies_4

Commitments and contingencies - AbbVie Alpha Synuclein Collaboration Agreement - (Details) - AbbVie Alpha Synuclein Collaboration Agreement - AbbVie $ in Thousands	1 Months Ended	3 Months Ended
	Feb. 28, 2019USD ($)item	Mar. 31, 2019USD ($)item
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of antibodies encoded by virus | item	1
Number of research antibodies | item	1
Non-refundable upfront payment received	$ 65,000
First Research Compound payment	80,000
Three additional research compounds payment to be received for each	$ 30,000
Number of additional research compounds | item	3
Milestone payments to be received for licensed compound in case Parkinson's disease indication	$ 450,000
Milestone payments to be received for licensed compound in case first indication other than Parkinson's disease	185,000
Milestone payments to be received for licensed compound for subsequent non-Parkinson's disease indication	$ 92,500
Binds to alpha-synuclein protein, after the termination date (in months)	18 months
Number of development options | item		4
Deferred revenue		$ 64,800
Revenue recognized		$ 200
Allocation of Transaction Price
Allocation of Transaction Price	$ 65,000
Minimum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Antibodies to include in Research Period | item	1
The number of Licensed Products | item	1
Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Antibodies to include in Research Period | item	4
Research Services
Allocation of Transaction Price
Allocation of Transaction Price	$ 23,768
First Development Option Material Right
Allocation of Transaction Price
Allocation of Transaction Price	41,232
Commercial Milestone
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Specified commercial milestone payments	$ 500,000

Commitments and contingencies_5

Commitments and contingencies - Neurocrine Collaboration Agreement - (Details) - Neurocrine Collaboration Agreement $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended
	Mar. 31, 2019USD ($)item$ / sharesshares	Mar. 31, 2019USD ($)$ / shares
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of collaboration programs | item	4
Number of discovery programs | item	2
Allocation of Transaction Price
Costs to obtain collaboration agreement		$ 800
AADC
Collaborative Arrangements and Non-collaborative Arrangement Transactions [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	45.00%
FA Program
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of profit or loss under co-co option after paying rate-shifting fee	40.00%
Neurocrine
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of targets | item	8
Upfront payment	$ 115,000
Purchase of common stock, shares | shares	4,179,728
Purchase of common stock	$ 50,000
Price per share | $ / shares	$ 11.9625	$ 11.9625
Estimated cost reimbursement		$ 431,300
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
Allocation of Transaction Price
Allocation of variable consideration	$ 431,273	431,273
Allocation of fixed consideration	87,383	87,383
Revenue recognized		1,900
Deferred revenue	$ 86,900	86,900
Neurocrine | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of reduction in royalty payments	50.00%
Neurocrine | AADC
Collaborative Arrangements and Non-collaborative Arrangement Transactions [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	55.00%
Allocation of Transaction Price
Allocation of variable consideration	$ 170,418	170,418
Allocation of fixed consideration	$ 76,023	76,023
Neurocrine | FA Program
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of profit or loss under co-co option after paying rate-shifting fee	60.00%
Allocation of Transaction Price
Allocation of variable consideration	$ 114,023	114,023
Allocation of fixed consideration	5,680	5,680
Neurocrine | Discovery program 1
Allocation of Transaction Price
Allocation of variable consideration	73,416	73,416
Allocation of fixed consideration	2,840	2,840
Neurocrine | Discovery program 2
Allocation of Transaction Price
Allocation of variable consideration	73,416	73,416
Allocation of fixed consideration	2,840	$ 2,840
Neurocrine | Development and regulatory milestones | AADC
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Aggregate maximum milestone payments to be received from collaborative partner	170,000
Neurocrine | Development and regulatory milestones | FA Program
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Aggregate maximum milestone payments to be received from collaborative partner	195,000
Neurocrine | Development and regulatory milestones | Discovery program 1
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Aggregate maximum milestone payments to be received from collaborative partner	130,000
Neurocrine | Development and regulatory milestones | Discovery program 2
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Aggregate milestone payments	130,000
Neurocrine | Commercial Milestone
Collaborative Arrangements and Non-collaborative Arrangement Transactions [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

Commitments and contingencies_6

Commitments and contingencies - Other Agreements - (Details) $ in Millions	1 Months Ended	3 Months Ended	12 Months Ended
	Feb. 28, 2015USD ($)	Mar. 31, 2019	Dec. 31, 2016USD ($)multiple	Dec. 31, 2017USD ($)	Sep. 30, 2016USD ($)
Collaborative Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Per Milestone, maximum milestone payments to be received from collaborative partner	$ 540
Various contract research organizations and institutions | Minimum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of days written notice required by reporting entity to terminate agreement		30 days
Various contract research organizations and institutions | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of days written notice required by reporting entity to terminate agreement		90 days
Non-profit organization agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Maximum funding			$ 4
Funding multiple | multiple			2.6
Milestone payment liability				$ 1
MRIC
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Amount of investment					$ 2

Preferred stock (Details)

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

Stock based compensation (Detai

Stock based compensation (Details)

Jan. 01, 2019shares

Jan. 01, 2018shares

Jan. 01, 2017shares

Jan. 01, 2016shares

Oct. 31, 2015shares

Jan. 31, 2014$ / sharesshares

Mar. 31, 2019USD ($)item$ / sharesshares

Mar. 31, 2018USD ($)shares

Dec. 31, 2016item

Dec. 31, 2018USD ($)$ / shares

Aug. 31, 2015shares

Apr. 30, 2015shares

Aug. 31, 2014shares

Apr. 30, 2014shares

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

Stock-based compensation | $

$ 3,518,000

$ 2,322,000

Stock options granted (in shares)

753,340

Exercise price | $ / shares

$ 14.99

$ 15.91

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]

Shares available for future issuance (in shares)

262,362

Common stock shares authorized for issuance

325,707

321,300

267,658

267,492

Period to purchase shares

6 months

Increase in ESSP shares (as a percent)

1.00%

2015 Employee Stock Purchase Plan | Minimum

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

Payroll deduction percentage

1.00%

2015 Employee Stock Purchase Plan | Maximum

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

Payroll deduction percentage

10.00%

2015 Stock Option Plan

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

Shares available for future issuance (in shares)

1,311,812

2,275,140

Percentage limit of issued and outstanding shares up to which additional shares may be issued

4.00%

Number of shares authorized for stock-based compensation plan (in shares)

1,302,830

1,285,200

1,070,635

1,069,971

Restricted stock units

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

Stock-based compensation | $

$ 683,000

294,000

Unrecognized stock-based compensation expense | $

$ 2,500,000

Vesting period

3 years

Restricted stock granted, original issued price (in dollars per share) | $ / shares

$ 9.10

Restricted stock units | 2015 Stock Option Plan

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

Restricted stock granted (in shares)

354,405

Founders restricted stock

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

Probable performance milestones | item

1

Performance milestones | item

3

Stock-based compensation | $

$ 0

200,000

$ 1,500,000

Compensation expense for remaining founders' awards | $

$ 0

Restricted stock granted (in shares)

1,188,233

Restricted stock granted, original issued price (in dollars per share) | $ / shares

$ 0.0425

Number of awards | item

2

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

Employees and directors stock options

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

Stock-based compensation | $

$ 2,800,000

1,900,000

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)

753,340

Non-employees stock options

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

Stock-based compensation | $

$ 32,000

$ 100,000

Stock options granted (in shares)

0

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

Non-employees stock options | 2015 Stock Option Plan

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

New stock options issued

0

Research and development

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

Stock-based compensation | $

$ 1,416,000

$ 1,198,000

General and administrative

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

Stock-based compensation | $

$ 2,102,000

$ 1,124,000

Stock based compensation - Comp

Stock based compensation - Compensation expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 3,518	$ 2,322
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	2,776	1,966
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	683	294
Employee stock purchase plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	59	62
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	1,416	1,198
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 2,102	$ 1,124

Stock based compensation - Rest

Stock based compensation - Restricted Stock - (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Restricted stock disclosures
Stock-based compensation	$ 3,518	$ 2,322
Restricted stock units
Shares
Granted (in shares)	354,405	0
Forfeited (in shares)	(2,790)
Balance, ending (in shares)	351,615
Weighted Average Grant Date Fair Value Per Share
Issued (in dollars per share)	$ 9.10
Forfeited (in dollars per share)	9.10
Balance, ending (in dollars per share)	$ 9.10
Restricted stock disclosures
Stock-based compensation	$ 683	$ 294
Unrecognized stock-based compensation expense	$ 2,500
Remaining weighted-average remaining vesting period	2 years 9 months 18 days
Employees restricted stock
Restricted stock disclosures
Stock-based compensation	$ 700

Stock based compensation - Stoc

Stock based compensation - Stock Options - (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding, beginning balance (in shares)	4,225,152
Granted (in shares)	753,340
Exercised (in shares)	(31,360)
Cancelled or forfeited (in shares)	(104,038)
Outstanding, ending balance (in shares)	4,843,094
Exercisable (in shares)	1,674,666
Vested and expected to vest (in shares)	4,843,094
Weighted Average Exercise Price
Outstanding (in dollars per share)	$ 15.91
Granted (in dollars per share)	9.32
Exercised (in dollars per share)	9.05
Cancelled or forfeited (in dollars per share)	12.93
Outstanding (in dollars per share)	14.99
Exercisable (in dollars per share)	13.07
Vested and expected to vest (in dollars per share)	$ 14.99
Remaining Contractual Life
Outstanding	8 years 6 months
Exercisable	7 years 6 months
Vested and expected to vest	8 years 6 months
Aggregate Intrinsic Value
Outstanding	$ 25,251,000
Exercisable	11,684,000
Vested and expected to vest	25,251,000
Options disclosures
Stock-based compensation	3,518,000	$ 2,322,000
Stock options
Options disclosures
Stock-based compensation	$ 2,776,000	$ 1,966,000
Employees and directors stock options
Options disclosures
Weighted average fair value of grants (in dollars per share)	$ 6.23	$ 16.49
Stock-based compensation	$ 2,800,000	$ 1,900,000
Non-employees stock options
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Granted (in shares)	0	0
Options disclosures
Stock-based compensation	$ 32,000	$ 100,000

Stock based compensation - Blac

Stock based compensation - Black-Scholes options pricing model - (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Fair value assumptions
Expected dividend yield	0.00%
Options disclosures
Stock-based compensation	$ 3,518,000	$ 2,322,000
Stock options granted (in shares)	753,340
Employees and directors stock options
Fair value assumptions
Risk-free interest rate	2.50%	2.70%
Expected term	6 years	6 years
Expected volatility	75.00%	74.30%
Options disclosures
Weighted average fair value of grants (in dollars per share)	$ 6.23	$ 16.49
Stock-based compensation	$ 2,800,000	$ 1,900,000
Non-employees stock options
Options disclosures
Stock-based compensation	$ 32,000	$ 100,000
Stock options granted (in shares)	0	0
Unvested stock options
Options disclosures
Unrecognized stock-based compensation expense	$ 27,500,000
Remaining weighted-average remaining vesting period	2 years 9 months 18 days

Net loss per share (Details)

Net loss per share (Details) - shares	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	5,430,003	7,222,956
Restricted common stock awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	235,294	412,150
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	351,615
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	4,843,094	6,810,806

Related party transactions (Det

Related party transactions (Details) - Investor - Consulting and management services - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Related Party Transaction [Line Items]
Total amount of services received	$ 0	$ 0
Accounts payable to related party	$ 0