Adverum Biotechnologies (ADVM) 10-K 12 Mar 20 2019 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Feb. 28, 2020	Jun. 30, 2019
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Entity Registrant Name	Adverum Biotechnologies, Inc.
Entity Central Index Key	0001501756
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Well-known Seasoned Issuer	Yes
Entity Public Float			$ 674.5
Entity Emerging Growth Company	false
Entity Small Business	true
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		79,681,257
Entity File Number	001-36579
Entity Tax Identification Number	20-5258327
Entity Incorporation, State or Country Code	DE
Entity Address, Address Line One	800 Saginaw Drive
Entity Address, City or Town	Redwood City
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94063
City Area Code	650
Local Phone Number	656-9323
Document Annual Report	true
Document Transition Report	false
Title of 12(b) Security	Common Stock, par value $0.0001 per share
Trading Symbol	ADVM
Security Exchange Name	NASDAQ
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Portions of the definitive proxy statement (the Proxy Statement) for the 2020 Annual Meeting of Stockholders of the registrant are incorporated by reference into Part III of this Annual Report on Form 10-K. If the Proxy Statement is not filed by April 29, 2020, then the registrant will file an amendment to this Form 10-K on Form 10-K/A to include the Part III information in this Form 10-K.

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 65,897	$ 154,949
Short-term investments	100,138	50,130
Prepaid expenses and other current assets	9,835	3,675
Total current assets	175,870	208,754
Operating lease right-of-use assets	20,963
Property and equipment, net	24,884	3,586
Restricted cash	999	999
Deposit and other non-current assets	11	156
Total assets	222,727	213,495
Current liabilities:
Accounts payable	4,103	1,707
Accrued expenses and other current liabilities	11,271	8,784
Lease liability, current portion	4,034
Deferred rent, current portion		228
Total current liabilities	19,408	10,719
Long-term liabilities:
Deferred rent, net of current portion		1,366
Lease liability, net of current portion	28,214
Other non-current liabilities	148	243
Total liabilities	47,770	12,328
Commitments and contingencies (Note 8)
Stockholders’ equity:
Preferred stock, $0.0001 par value, 5,000 shares authorized; no shares issued and outstanding
Common stock, $0.0001 par value, 300,000 shares authorized at December 31, 2019: 67,329 and 62,965 shares issued and outstanding at December 31, 2019 and 2018, respectively	7	6
Additional paid-in capital	560,704	522,503
Accumulated other comprehensive loss	(725)	(799)
Accumulated deficit	(385,029)	(320,543)
Total stockholders’ equity	174,957	201,167
Total liabilities and stockholders’ equity	$ 222,727	$ 213,495

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
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	$ 0.0001	$ 0.0001
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	67,329,000	62,965,000
Common stock, shares outstanding	67,329,000	62,965,000

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Statement [Abstract]
Collaboration and license revenue	$ 250,000	$ 1,612,000
Type of Revenue [Extensible List]	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Operating expenses:
Research and development	$ 40,419,000	$ 50,133,000
General and administrative	28,376,000	24,560,000
Impairment of goodwill and intangible assets		5,000,000
Total operating expenses	68,795,000	79,693,000
Operating loss	(68,545,000)	(78,081,000)
Other income:
Other income, net	4,059,000	4,204,000
Net loss before income taxes	(64,486,000)	(73,877,000)
Income tax benefit	0	1,250,000
Net loss	(64,486,000)	(72,627,000)
Other comprehensive income:
Net unrealized gain on marketable securities	33,000	168,000
Foreign currency translation adjustment	41,000	(4,000)
Comprehensive loss	$ (64,412,000)	$ (72,463,000)
Net loss per share - basic and diluted	$ (1.01)	$ (1.18)
Weighted-average common shares outstanding-basic and diluted	64,102	61,375

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Private Placement [Member]	Common Stock [Member]	Common Stock [Member]Private Placement [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member]Private Placement [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]
Balance at Dec. 31, 2017	$ 184,028		$ 5		$ 439,048		$ (963)	$ (254,062)
Balance, shares at Dec. 31, 2017			49,015
Issuance of common stock net of issuance costs	70,187		$ 1		70,186
Issuance of common stock net of issuance costs, shares			11,642
Adoption of Topic 606	6,146							6,146
Stock-based compensation expense	13,432				13,432
Common stock issued upon exercise of stock options	688				688
Common stock issued upon exercise of stock options, shares			1,606
Common stock issued under employee stock purchase plan	340				340
Common stock issued under employee stock purchase plan, shares			120
Common stock issued upon release of restricted stock units, shares			774
Restricted stock surrendered for taxes	(1,191)				(1,191)
Restricted stock surrendered for taxes, shares			(192)
Net unrealized gain on marketable securities	168						168
Foreign currency translation adjustments	(4)						(4)
Net loss	(72,627)							(72,627)
Balance at Dec. 31, 2018	201,167		$ 6		522,503		(799)	(320,543)
Balance, shares at Dec. 31, 2018			62,965
Issuance of common stock net of issuance costs	25,755	$ 134	$ 1		25,754	$ 134
Issuance of common stock net of issuance costs, shares			2,436	20
Stock-based compensation expense	9,899				9,899
Common stock issued upon exercise of stock options	3,442				3,442
Common stock issued upon exercise of stock options, shares			1,397
Common stock issued under employee stock purchase plan	442				442
Common stock issued under employee stock purchase plan, shares			86
Common stock issued upon release of restricted stock units, shares			663
Restricted stock surrendered for taxes	(1,470)				(1,470)
Restricted stock surrendered for taxes, shares			(238)
Net unrealized gain on marketable securities	33						33
Foreign currency translation adjustments	41						41
Net loss	(64,486)							(64,486)
Balance at Dec. 31, 2019	$ 174,957		$ 7		$ 560,704		$ (725)	$ (385,029)
Balance, shares at Dec. 31, 2019			67,329

Consolidated Statements of St_2

Consolidated Statements of Stockholders' Equity (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Statement Of Stockholders Equity [Abstract]
Issuance costs	$ 1,065	$ 4,140

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net loss	$ (64,486)	$ (72,627)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,573	1,750
Stock-based compensation expense	9,899	13,432
Amortization of premium and discounts on marketable securities, net	(1,273)	24
Accreted interest on BPI	22	95
Impairment of goodwill and intangible assets		5,000
Other	36	(17)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(5,954)	(793)
Deposit and other long-term assets		(16)
Operating lease right-of-use assets	2,168
Accounts payable	(650)	(67)
Accrued expenses and other current liabilities	1,909	215
Deferred revenue		(953)
Deferred rent		1,243
Lease liability	7,586
Deferred tax liability		(1,250)
Net cash used in operating activities	(49,170)	(53,964)
Cash flows from investing activities:
Purchases of marketable securities	(197,343)	(78,726)
Maturities of marketable securities	148,517	148,979
Purchases of property and equipment	(19,247)	(809)
Net cash provided by (used in) provided by investing activities	(68,073)	69,444
Cash flows from financing activities:
Proceeds from offering of common stock, net of issuance costs	25,755	70,187
Proceeds from issuance of common stock through private placement	134
Proceeds from issuance of common stock pursuant to option exercises	3,442	688
Taxes paid related to net share settlement of restricted stock units	(1,470)	(1,191)
Proceeds from employee stock purchase plan	442	340
Repayment of BPI loan	(112)	(175)
Proceeds from a financing arrangement		100
Net cash provided by financing activities	28,191	69,949
Net increase (decrease) in cash and cash equivalents and restricted cash	(89,052)	85,429
Cash and cash equivalents and restricted cash at beginning of period	155,948	70,519
Cash and cash equivalents and restricted cash at end of period	66,896	155,948
Supplemental schedule of noncash investing information
Fixed assets in accounts payable and current liabilities	$ 5,242	$ 1,616

Description of the Business

Description of the Business	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Description of the business	1. Description of the business Nature of Business —Adverum Biotechnologies, Inc. (the “Company” or “Adverum”) was incorporated in Delaware on July 17, 2006 and is headquartered in Redwood City, California. The Company is a clinical-stage gene therapy company targeting unmet medical needs in ocular and rare diseases. The Company develops gene therapy product candidates designed to provide durable efficacy by inducing sustained expression of a therapeutic protein. The Company’s core capabilities include clinical development, novel vector discovery, and in house manufacturing expertise, specifically in scalable process development, assay development, and current Good Manufacturing Practices (“cGMP”) quality control. Since the Company’s inception, it has devoted its efforts to performing research and development activities, filing patent applications, hiring personnel and raising capital to support these activities The Company has not generated any revenue from the sale of products since its inception. The Company has experienced net losses since its inception and had an accumulated deficit of $385.0 million as of December 31, 2019. The Company expects to incur losses and have negative net cash flows from operating activities as it engages in further research and development activities. The Company believes that it has sufficient funds to continue operations into 2022.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of significant accounting policies Basis of Presentation and Principles of Consolidation — The Company’s consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”). The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All inter-company transactions and balances have been eliminated in consolidation. Use of Estimates —The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, and the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of income and expenses during the reporting period. The Company bases estimates and assumptions on historical experience when available and on various factors that it believes to be reasonable under the circumstances. The Company evaluates its estimates and assumptions, including those related to research and development expense accruals, stock-based compensation expense, income taxes, fair values of financial instruments, and incremental borrowing rate. The Company’s actual results may differ from these estimates under different assumptions or conditions. There have been no significant changes from the Company’s original estimates in any periods presented. Foreign Currency Translation —The Company’s consolidated financial statements are prepared in U.S. dollars. The Company’s foreign subsidiaries use the Euro and Australian dollar as their functional currencies and maintain their records in their local currencies, except its Ireland subsidiary that uses the U.S. dollar as its functional currency. Assets and liabilities are re-measured at exchange rates in effect at the end of the reporting period for the Company’s French and Australian subsidiaries, and at historical exchange rates for its Irish subsidiary. Equity is measured at historical rates and income and expenses are re-measured at average exchange rates for the reporting period. The resulting foreign currency translation adjustment is recorded in accumulated other comprehensive loss in the consolidated balance sheet. Transactions denominated in foreign currency are translated at exchange rates at the date of transaction with foreign currency gains (losses) recorded in other comprehensive income, net in the consolidated statements of operations and comprehensive loss. Cash and Cash Equivalents —The Company considers all highly liquid investments purchased with original maturities of three months or less at the date of purchase to be cash equivalents. Cash and cash equivalents include cash held in banks, money market accounts and highly liquid debt securities. Cash equivalents are stated at fair value. Restricted Cash —Restricted cash primarily consists of cash collateral to letter of credit provided to the landlord in relation to a lease agreement (see Note 5). Short-Term Investments —All short-term investments, which consist of debt securities and certificates of deposit, have been classified as “available for sale” and are carried at fair value. Unrealized gains and losses, net of any related tax effects, are excluded from earnings and are included in other comprehensive loss and reported as a separate component of stockholders’ equity until realized. Realized gains and losses and declines in value judged to be other than temporary, if any, on available-for-sale securities are included in other income (expense), net in the Company’s consolidated statements of operations and comprehensive loss. The cost of securities sold is based on the specific-identification method. The amortized cost of securities is adjusted for amortization of premiums and accretion of discounts to maturity. Interest on short-term investments is included in other income, net in the Company’s consolidated statements of operations and comprehensive loss. In accordance with the Company’s investment policy, management invests to diversify credit risk and only invests in securities with high credit quality, including U.S. government securities. The Company periodically evaluates whether declines in the fair value of its investments below their cost are other than temporary. The evaluation includes consideration of the cause of the impairment, including the creditworthiness of the security issuers, the number of securities in an unrealized loss position, the severity and duration of the unrealized losses, whether the Company has the intent to sell the securities, and whether it is more likely than not that the Company will be required to sell the securities before the recovery of their amortized cost basis. If the Company determines that the decline in fair value of an investment is below its accounting basis and this decline is other than temporary, the Company would reduce the carrying value of the security it holds and records a loss for the amount of such decline. The Company has not recorded any realized losses or declines in value judged to be other than temporary on its investments. Segment Reporting —The Company operates and manages its business as one reporting and operating segment, which is the business of developing and commercializing gene therapeutics. The Company’s chief executive officer, who is the chief operating decision maker, reviews financial information on an aggregate basis for purposes of allocating resources and evaluating financial performance. Concentrations of Credit Risk and Other Uncertainties —Financial instruments that potentially subject the Company to significant concentrations of credit risk consists primarily of cash, cash equivalents and short-term investments. Risks associated with cash, cash equivalents, short-term investments are mitigated by the Company’s investment policy, which limits the Company’s investing to only those marketable securities rated at least A-1/P-1 Short Term Rating and A/A2 Long Term Rating, as determined by independent credit rating agencies. Management believes that the Company is not exposed to significant credit risk. The Company is subject to certain risks and uncertainties, including, but not limited to changes in any of the following areas that the Company believes could have a material adverse effect on future financial position or results of operations: ability to obtain future financing; regulatory approval and market acceptance of, and reimbursement for, the Company’s product candidates; performance of third-party clinical research organizations and manufacturers; development of sales channels; protection of the intellectual property; litigation or claims against the Company based on intellectual property, patent, product, regulatory or other factors; and the Company’s ability to attract and retain employees necessary to support the growth. Property and Equipment —Property and equipment are recorded at cost, net of accumulated depreciation and amortization. Depreciation is recorded using the straight-line method over the estimated useful lives of the assets, generally three to five years. Leasehold improvements are capitalized and amortized over the shorter period of their expected lives or the lease term. Major replacements and improvements are capitalized, while general repairs and maintenance are expensed as incurred. Valuation of Long-Lived Assets and Purchased Intangible Assets —The Company evaluates the carrying value of amortizable long‑lived assets, whenever events, or changes in business circumstances or the planned use of long‑lived assets indicate that their carrying amounts may not be fully recoverable or that their useful lives are no longer appropriate. If these facts and circumstances exist, the Company assesses for recovery by comparing the carrying values of long‑lived assets with their future undiscounted net cash flows. If the comparison indicates that impairment exists, long‑lived assets are written down to their respective fair values based on discounted cash flows. Significant management judgment is required in the forecasting of future operating results that is used in the preparation of expected undiscounted cash flows. If management’s assumptions about future operating results were to change as a result of events or circumstances, the Company may be required to record an impairment loss on these assets. There were no impairment indicators noted for the Company’s amortizable long-lived assets, fixed assets, in the year ended December 31, 2019. The Company also evaluates the carrying value of intangible asset (not subject to amortization) related to in‑process research and development (“IPR&D”) asset, which is considered to be indefinite‑lived until the completion or abandonment of the associated research and development efforts. Accordingly, amortization of the IPR&D assets will not occur until the product reaches commercialization. During the period the intangible asset is considered indefinite‑lived, it will be tested for impairment on an annual basis, as well as between annual tests if the Company becomes aware of any events occurring or changes in circumstances that would indicate that the fair value of the IPR&D asset is less than its carrying amount. If and when development is complete, which generally occurs when regulatory approval to market the product is obtained, the associated IPR&D asset would be deemed definite‑lived and would then be amortized based on its estimated useful life at that point in time based on respective patent term. If a potential impairment exists, an impairment loss is measured as the excess of the asset’s carrying value over its fair value. During the year ended December 31, 2018, the Company recorded an impairment charge of $5.0 million related to its intangible assets. Revenue Recognition —The Company has primarily generated revenue through license, research and collaboration arrangements with its strategic partners. Under Topic 606, the Company recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the Company expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that the Company determines are within the scope of ASC 606, the Company performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the Company satisfies a performance obligation. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. The Company’s license and collaboration arrangements with Editas Medicine, Inc. (“Editas”) and GenSight Biologics (“GenSight”) are within the scope of Topic 606. Collaboration Agreement with Editas — Under Topic 606, the transaction price at contract inception was determined to be $1.0 million, which was related to the non-refundable upfront payment for license and research services. The transaction price of $1.0 million at contract inception was allocated to a single performance obligation. During the year ended December 31, 2018, the Company recognized revenue of $1.5 million associated with the Editas collaboration agreement. The remaining performance obligations for Editas were completed during 2018. During the year ended December 31, 2019, the Company had no recognized revenue from the Editas collaboration agreement. There was no outstanding deferred revenue associated with Editas as of December 31, 2019 and 2018. License Agreement with GenSight — On February 2014, the Company entered into an agreement with GenSight, where the Company granted GenSight a non-exclusive license to its proprietary AAV.7m8 vector. Under the agreement, the Company is eligible to receive development, regulatory and commercial milestones. Also, the Company is eligible to receive low to mid-single digit royalties on sales of GenSight’s licensed products. During the years ended December 31, 2019 and 2018, GenSight achieved clinical development milestones pursuant to the agreement. This milestone was previously constrained under Topic 606. The Company earned milestone payments of $250,000 and $150,000, which were recognized as revenue for the years ended December 31, 2019 and 2018, respectively. Research and Development Expenses —Research and development expenses are charged to expense as incurred. Research and development expenses include primarily personnel-related costs, stock-based compensation expense, laboratory supplies, consulting costs, external contract research and development expenses, including expenses incurred under agreements with CROs, the cost of acquiring, developing and manufacturing clinical trial materials, and overhead expenses, such as rent, equipment depreciation, insurance and utilities. Advance payments for goods or services for future research and development activities are deferred and expensed as the goods are delivered or the related services are performed. The Company estimates preclinical studies and clinical trial expenses based on the services performed pursuant to contracts with research institutions and clinical research organizations that conduct and manage preclinical studies and clinical trials on the Company’s behalf. In accruing service fees, the Company estimates the time period over which services will be performed and the level of effort to be expended in each period. These estimates are based on communications with the third-party service providers and the Company’s estimates of accrued expenses and on information available at each balance sheet date. If the actual timing of the performance of services or the level of effort varies from the estimate, the Company will adjust the accrual accordingly. There have been no significant changes from the Company’s original estimates in any of the periods presented. Fair Value Measurements —Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. The carrying amounts of the Company’s financial instruments, including cash equivalents, prepaid and other current assets, accounts payable, accrued expenses and other current liabilities approximate their fair values due to their short-term maturities. Refer to Note 3 for the methodologies and assumptions used in valuing financial instruments. Stock-based Compensation Expense —Stock-based compensation expense related to stock awards to employees is measured at fair value of the award on the date of the grant. The Company estimates the grant-date fair value, and the resulting stock-based compensation expense, using the Black-Scholes valuation model for stock options and using intrinsic value, which is the closing price of its common stock on the date of the grant, for the restricted stock units (“RSUs”). The fair value of the award that is ultimately expected to vest is recognized as expense on a straight-line basis over the requisite service period, which is generally the vesting period. The Black-Scholes valuation model requires the use of following assumptions: Expected Term —The expected term assumption represents the period that the Company’s stock-based awards are expected to be outstanding and is determined using the simplified method. Expected Volatility —Expected volatility is estimated using a weighing of comparable public companies’ volatility for similar terms and the Company’s historical volatility. Expected Dividend —The Black-Scholes valuation model calls for a single expected dividend yield as an input. The Company has never paid dividends and has no plans to pay dividends. Risk-Free Interest Rate —The risk-free interest rate is based on the U.S. Treasury zero-coupon issues in effect at the time of grant for periods corresponding with the expected term of option. Income Taxes —The Company accounts for income taxes using the asset and liability method. The Company recognizes deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements or tax returns. Deferred tax assets and liabilities are determined based on the difference between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. In evaluating the ability to recover its deferred income tax assets, the Company considers all available positive and negative evidence, including its operating results, ongoing tax planning and forecasts of future taxable income on a jurisdiction-by-jurisdiction basis. In the event the Company determines that it would be able to realize its deferred income tax assets in the future in excess of their net recorded amount, it would make an adjustment to the valuation allowance that would reduce the provision for income taxes. Conversely, in the event that all or part of the net deferred tax assets are determined not to be realizable in the future, an adjustment to the valuation allowance would be charged to earnings in the period when such determination is made. As of December 31, 2019 and 2018, the Company has recorded a full valuation allowance on its deferred tax assets. Tax benefits related to uncertain tax positions are recognized when it is more likely than not that a tax position will be sustained upon examination. Interest and penalties related to unrecognized tax liabilities are included within the provision for income tax. Comprehensive Loss —Comprehensive loss comprises net loss and other comprehensive income. Other comprehensive income consists of foreign currency translation adjustments related to translation of the financial statements of the Company’s Australia and France subsidiaries and unrealized gain on marketable securities. The Company did not record reclassifications from other comprehensive income (loss) to the income (loss) during the years ended December 31, 2019 and 2018. Basic and Diluted Net Loss Per Share — Basic net loss per share is calculated by dividing the net loss by the weighted-average number of shares of common stock outstanding for the period. Diluted net loss per share is computed by giving effect to all potential dilutive common stock equivalents outstanding for the period using the treasury stock method. Outstanding stock options, restricted stock units (“RSUs”), employee stock purchase plan (“ESPP”) and warrants are considered to be common stock equivalents and are only included in the calculation of diluted net loss per share when their effect is dilutive. Recently Adopted Accounting Pronouncements Leases The Company adopted Accounting Standards Update (ASU) No. 2016-02, Leases (Topic 842) (“Topic 842”) on January 1, 2019. For its long-term operating leases, the Company recognizes a right-of-use asset and a lease liability on its consolidated balance sheets. The Company adopted the new standard using the modified retrospective approach and, upon adoption, recorded a lease liability of $24.7 million, and a right‑to‑use asset of $23.1 million, and made no adjustment to the accumulated deficit. In connection with the adoption of the lease standard, the Company also derecognized deferred rent of $1.5 million. The adoption of Topic 842 did not have an impact on the consolidated statement of operations. The lease liability is determined as the present value of future lease payments using an estimated rate of interest that the Company would pay to borrow equivalent funds on a collateralized basis at the lease commencement date. In order to estimate the incremental borrowing rate, management estimated its credit rating, adjusted the credit rating for the nature of the collateral, and benchmarked the borrowing rate against observable yields on comparable securities with a similar term. As of the adoption date, the Company estimated the incremental borrowing rate to be 8.5%. The Company based the right-of-use asset on the liability adjusted for any prepaid or deferred rent. The Company determined the lease term at the commencement date by considering whether renewal options and termination options are reasonably assured of exercise. Rent expense for the operating lease is recognized on a straight-line basis over the lease term and is included in operating expenses on the statements of operations and comprehensive loss. Variable lease payments include lease operating expenses. The Company elected the practical expedients permitted under Topic 842, which among other things, allowed the Company to carry forward the historical lease classification of those leases in place as of January 1, 2019. The Company elected to exclude from its consolidated balance sheets recognition of leases having a term of 12 months or less (short-term leases) and elected to not separate lease components and non-lease components for its long-term real-estate leases. Share-based payment to nonemployees In June 2018, the FASB issued ASU 2018-07, “Compensation – Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting” (“Topic 718”) that expands the scope of Topic 718 to include share-based payment transactions for acquiring goods and services from nonemployees. The Company adopted ASU 2018–07 on January 1, 2019 and the impact of the adoption resulted in lower stock-based compensation of $1.4 million during the year ended December 31, 2019. Under the new standard, our share-based payment transactions with non-employees have a fixed measurement and are not remeasured over the vesting period.

Fair Value Measurements and Fai

Fair Value Measurements and Fair Value of Financial Instruments	12 Months Ended
	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurements and Fair Value of Financial Instruments	3. Fair Value Measurements and Fair Value of Financial Instruments The authoritative guidance on fair value measurements establishes a three-tier fair value hierarchy for disclosure of fair value measurements as follows: Level 1: Quoted prices in active markets for identical assets or liabilities. Level 2: Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3: Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The Company’s assessment of the significance of a particular input to the fair value measurement in its entirety requires management to make judgments and consider factors specific to the asset or liability. The fair value of Level 1 securities is determined using quoted prices in active markets for identical assets. Level 1 securities consist of highly liquid money market funds. Financial assets and liabilities are considered Level 2 when their fair values are determined using inputs that are observable in the market or can be derived principally from or corroborated by observable market data such as pricing for similar securities, recently executed transactions, cash flow models with yield curves, and benchmark securities. In addition, Level 2 financial instruments are valued using comparisons to like-kind financial instruments and models that use readily observable market data as their basis. U.S. government and agency securities, commercial paper, corporate bond and certificates of deposit are valued primarily using market prices of comparable securities, bid/ask quotes, interest rate yields and prepayment spreads and are included in Level 2. During the periods presented, the Company has not changed the manner in which it values liabilities that are measured at estimated fair value using Level 3 inputs. There were no transfers within the hierarchy during the years ended December 31, 2019 and 2018. The following is a summary of the Company’s cash equivalents and short-term investments (in thousands): December 31, 2019 Amortized Cost Basis Unrealized Gains Unrealized Loses Estimated Fair Value Level 1 Money market funds $ 15,056 $ — $ — $ 15,056 Level 2 U.S. government and agency securities 37,974 14 (2 ) 37,986 Commercial paper 87,983 8 (8 ) 87,983 Corporate bonds 10,495 6 — 10,501 Total cash equivalents and short-term investments 151,508 28 (10 ) 151,526 Less: Cash equivalents (51,391 ) — 3 (51,388 ) Total short-term investments $ 100,117 $ 28 $ (7 ) $ 100,138 December 31, 2018 Amortized Cost Basis Unrealized Gains Unrealized Loses Estimated Fair Value Level 1 Money market funds $ 126 $ — $ — $ 126 Level 2 U.S. government and agency securities 25,792 1 (4 ) 25,789 Commercial paper 147,606 — — 147,606 Corporate bonds 27,778 5 (17 ) 27,766 Certificates of deposit 1,420 — — 1,420 Total cash equivalents and short-term investments 202,722 6 (21 ) 202,707 Less: Cash equivalents (152,577 ) — — (152,577 ) Total short-term investments $ 50,145 $ 6 $ (21 ) $ 50,130 Management determined that the gross unrealized losses on the Company’s marketable securities as of December 31, 2019 were temporary in nature. Therefore, none of the Company’s marketable securities were other-than-temporarily impaired as of December 31, 2019. All investments as of December 31, 2019 have a remaining maturity of one year or less. There were no transfers within the hierarchy during the years ended December 31, 2019 and 2018. Non-financial assets such as intangible assets, property, plant, and equipment are evaluated for impairment and adjusted to their fair value using Level 3 inputs, only when impairment is recognized. Fair values are considered Level 3 when management makes significant assumptions in developing a discounted cash flow model based upon a number of considerations, including projections of revenues, earnings and a discount rate.

Revenue

Revenue	12 Months Ended
	Dec. 31, 2019
Revenue From Contract With Customer [Abstract]
Revenue	4. Revenue Editas — In January 2018, the Company entered into an agreement to amend its collaboration, option and license agreement with Editas Medicine, Inc. The Company originally entered into an agreement with Editas in August 2016 pursuant to which the Company and Editas collaborated on certain studies using AAV vectors in connection with Editas’ genome editing technology and the Company granted to Editas an exclusive option to obtain certain exclusive rights to use the Company’s proprietary vectors in up to five ophthalmic indications. Under the terms of the agreement, as amended, Editas had until November 2018 to exercise the option with respect to a designated initial indication, which Editas declined to do. With respect to the four other indications, Editas had until August 2019 to exercise the option, otherwise all options would expire. Editas did not exercise the option, and the agreement terminated on August 8, 2019. Under Topic 606, the transaction price is $1.5 million, which includes the $1.0 million non-refundable upfront payment for license and research services at contract inception and the one-time, non-refundable cash payment of $0.5 million made by Editas in February 2018 in consideration for extending the agreement. The transaction price of $1.5 million was allocated to a single performance obligation: research and development. During the year ended December 31, 2018, the Company recognized revenue of $1.5 million associated with Editas. The remaining performance obligations for Editas were completed during 2018. During the year ended December 31, 2019, the Company had no recognized revenue from the Editas collaboration agreement. The Company had no deferred revenue balance as of December 31, 2019 and 2018. GenSight — In February 2014, the Company entered into an agreement with GenSight Biologics, S.A, in which the Company granted GenSight a non-exclusive license to its proprietary AAV.7m8 vector to develop gene therapy products to deliver certain therapeutic transgenes. Under the agreement, the Company is eligible to receive development, regulatory and commercial milestones. Also, the Company is eligible to receive low to mid-single digit royalties on sales of GenSight’s licensed products. During the year ended December 31, 2019 and 2018, GenSight achieved clinical development milestones pursuant to the agreement. These milestones were previously constrained under Topic 606. The Company earned milestone payments of $250,000 and $150,000, which was recognized as revenue for the years ended December 31, 2019 and 2018, respectively.

Leases

Leases	12 Months Ended
	Dec. 31, 2019
Leases [Abstract]
Leases	5. Leases In June 2018, the Company entered into an operating lease agreement for new office and laboratory space which consists of approximately 81,000 square feet located in Redwood City, California. The lease term is 10 years beginning September 2018 through February 2029 with two options to extend the lease term for a period of seven years each. The Company has the right to make tenant improvements, including the addition of laboratory space, with a lease incentive allowance of $8.1 million. The rent payments began on March 1, 2019. The lease agreement provides for an escalation of rent payments each year after an abatement period. In connection with the lease, the Company has provided the landlord with a letter of credit in the amount of $1.0 million. The security for the letter of credit of $1.0 million is classified as restricted cash under long term assets on the consolidated balance sheet. The Company also has an operating lease agreement for its Menlo Park office building which expires on May 8, 2020. The Company does not intend to exercise the option to extend the term. The Company adopted Topic 842 (See Note 2) and recorded right-of-use assets of $23.1 million and a lease liability of $24.7 million as of January 1, 2019. The estimated incremental borrowing rate used to measure the lease liability is 8.5%. Rent expense for the year ended December 31, 2019 and 2018 was $6.5 million, and $3.3 million, respectively, which includes variable lease costs for utilities, parking, maintenance, and real estate taxes. Variable lease expenses for the year ended December 31, 2019 was $1.6 million. The undiscounted future non-cancellable lease payments under the Company’s operating leases as of December 31, 2019 is as follows: Years ending December 31, (In thousands) 2020 $ 4,221 2021 4,683 2022 4,846 2023 5,016 2024 5,191 Thereafter 23,646 Total undiscounted lease payments 47,603 Less: Present value adjustments (15,355 ) Total $ 32,248

Balance Sheet Components

Balance Sheet Components	12 Months Ended
	Dec. 31, 2019
Balance Sheet Related Disclosures [Abstract]
Balance Sheet Components	6. Balance Sheet Components Property and Equipment, Net Property and equipment, net consists of the following: December 31, 2019 2018 (In thousands) Computer equipment and software $ 752 $ 646 Laboratory equipment 6,291 5,470 Furniture and fixtures 678 678 Leasehold improvements 1,602 1,602 Construction in progress 23,553 1,612 Total property and equipment 32,876 10,008 Less accumulated depreciation and amortization (7,992 ) (6,422 ) Property and equipment, net $ 24,884 $ 3,586 Construction in progress was $23.6 million as of December 31, 2019 and $1.6 million as of December 31, 2018, representing the construction costs incurred for the Company’s new facility in Redwood City, CA, which the Company began occupying in January 2020. Depreciation and amortization expense related to property and equipment was $1.6 million and $1.8 million and for the years ended December 31, 2019 and 2018, respectively. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consist of the following: December 31, 2019 2018 (In thousands) Compensation expense $ 4,055 $ 2,944 Accrued professional fees 2,607 2,291 Accrued preclinical costs 1,002 289 Accrued clinical and process development costs 971 1,561 Other 2,636 1,699 Total accrued expenses and other current liabilities $ 11,271 $ 8,784

Financing Arrangements

Financing Arrangements	12 Months Ended
	Dec. 31, 2019
Debt Disclosure [Abstract]
Financing Arrangements	7. Financing Arrangements Banque Publique d’Investissement (“BPI France”) Agreement In August 2015, BPI France granted Annapurna a €0.8 million interest-free conditional advance, of which €0.5 million was outstanding as of December 31, 2016. Payments are scheduled in equal quarterly amounts of €25,000 from September 30, 2017 to June 30, 2022. This payment schedule will be modified if the Company will receive revenue from license or product sales before advances are paid in full. The Company calculated 7% imputed interest expense on these advances that was recorded as a discount at the issuance date. The discount is amortized as interest expense over the life of the advances. As of December 31, 2019, the total carrying value, which approximates the fair value, of the conditional advance was $0.2 million, of which $0.1 million was recorded within other non-current liabilities and $0.1 million within accrued expenses and other current liabilities in the Company’s consolidated balance sheets. As of December 31, 2018, the total carrying value, which approximates the fair value, of the conditional advance was $0.3 million, of which $0.2 million was recorded within other non-current liabilities and $0.1 million within accrued expenses and other current liabilities in the Company’s consolidated balance sheets.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2019
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	8. Commitments and Contingencies Collaborations and License Agreements The Company is a party to various agreements, principally relating to licensed technology that requires future payments relating to milestones or royalties on future sales of specified products. Through December 31, 2018, none of the goals had been achieved under the license agreements and no milestones were accrued or payable. Because the achievement of these milestones is not fixed and determinable, such commitments have not been included on the Company’s consolidated balance sheets. The Company was a party to a master services agreement (“MSA”) with Cornell University (“Cornell”) originally established in August 2014 and amended in December 2015. Under the MSA, Cornell provided assistance in regulatory affairs, overall project management, and parameter development. This MSA included services relating to gene therapy programs directed to A1AT deficiency, HAE and severe allergy. The MSA, as amended, provided for the Company to pay Cornell $13.3 million ratably over four years for these services as services were performed. In December 2016, the Company informed Cornell that the Company decided to terminate the MSA for material breach, effective January 6, 2017. Subsequently, Cornell informed the Company that it disputed the validity of the Company’s termination of the MSA. In June 2019, Cornell and the Company entered into a settlement agreement, as a result of which the Company paid Cornell a $2.0 million settlement payment. There was no current period expense from the settlement, as the estimated costs associated with the termination of the MSA were previously accrued during the year ended December 31, 2017. The Company’s license agreements with Cornell for A1AT deficiency and HAE remain in effect. Guarantees and Indemnifications In the normal course of business, the Company enters into contracts and agreements that contain a variety of representation and warranties and provide for indemnification for certain liabilities. The exposure under these agreements is unknown because it involves claims that may be made against the Company in the future but have not yet been made. To date, the Company has not paid any claims or been required to defend any action related to its indemnification obligations. However, the Company may record charges in the future as a result of these indemnification obligations. The Company also has indemnification obligations to its directors and executive officers for specified events or occurrences, subject to some limits, while they are serving at the Company’s request in such capacities. There have been no claims to date and the Company believes the fair value of these indemnification agreements is minimal. Accordingly, the Company has not recorded any liabilities for these agreements as of December 31, 2019 and 2018. Legal Proceedings From time to time, the Company may become involved in litigation and other legal actions. The Company estimates the range of liability related to any pending litigation where the amount and range of loss can be estimated. The Company records its best estimate of a loss when the loss is considered probable. Where a liability is probable and there is a range of estimated loss with no best estimate in the range, the Company records a charge equal to at least the minimum estimated liability for a loss contingency when both of the following conditions are met: (i) information available prior to issuance of the financial statements indicates that it is probable that a liability had been incurred at the date of the financial statements and (ii) the range of loss can be reasonably estimated.

Common Stock Warrants

Common Stock Warrants	12 Months Ended
	Dec. 31, 2019
Warrants And Rights Note Disclosure [Abstract]
Common Stock Warrants	9. Common Stock Warrants The table below represents the outstanding warrants to purchase common stock as of December 31, 2019 and 2018: Issue Date Expiration Date Number of Warrant Shares Outstanding and Exercisable Exercise Price Per Share 12/31/2015 10/15/2020 40,000 $ 10.51 9/28/2017 9/29/2022 40,000 $ 3.65 8/4/2016 8/3/2021 10,000 $ 4.33 90,000 In February 2020, the warrants for the purchase of 10,000 shares of common stock issued in 2016 were net exercised for 7,250 shares of common stock.

Stock Plans

Stock Plans	12 Months Ended
	Dec. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock Plans	10. Stock Plans On December 26, 2006, the Company adopted the 2006 Equity Incentive Plan, which was amended by the board of directors on November 15, 2012 (the “2006 Plan”). The 2006 Plan allowed for the granting of incentive stock options (“ISOs”) and non-qualified stock options (“NSOs”) to the employees, members of the board of directors and consultants of the Company. ISOs were granted only to the Company’s employees, including officers and directors who are also employees. NSOs were granted to the employees and consultants. In July 2014, the Company’s board of directors and its stockholders approved the establishment of the 2014 Equity Incentive Award Plan (the “2014 Plan”). Options may no longer be issued under the 2006 Plan after July 30, 2014. In addition, the 2014 Plan provides for annual increases in the number of shares available for issuance thereunder on the first business day of each fiscal year, beginning with the year ended December 31, 2015, equal to four percent (4%) of the number of shares of the Company’s common stock outstanding as of such date or a lesser number of shares as determined by the Company’s board of directors. In October 2017, the Company adopted the 2017 Inducement Plan (the “Inducement Plan”). The Company reserved 600,000 shares for issuance pursuant to stock options and RSUs under the Inducement Plan. The only persons eligible to receive grants of stock options and RSUs under Inducement Plan are individuals who satisfy the standards for inducement grants under Nasdaq guidance that is, generally, a person not previously an employee or director of Adverum, or following a bona fide period of non-employment, as an inducement material to the individual's entering into employment with Adverum. The 2006 Plan, 2014 Plan and Inducement Plan are referred to collectively as the Plans. As of December 31, 2019, a total of 24,372,087 shares of common stock were reserved for issuance and 4,369,053 shares were available for future grants under the Plans. Stock Options Stock options under the 2014 Plan and the Inducement Plan may be granted for periods of up to 10 years and at prices no less than 100% of the estimated fair value of the shares on the date of grant as determined by the board of directors, provided, however, that the exercise price of an ISO and NSO granted to a 10% stockholder may not be less than 110% of the estimated fair value of the shares on the date of grant. Stock options granted to employees and non-employees generally vest ratably over four years. The following table summarizes stock option activity under the Company’s stock plans and related information: (In thousands, except exercise prices and years) Options Outstanding Weighted- Average Exercise Price Weighted- Average Remaining Contract Life (in years) Aggregate Intrinsic Value (a) Balance at December 31, 2017 6,695 $ 4.51 7.4 $ 9,539 Granted 2,049 5.94 Exercised (1,606 ) 0.43 Cancelled/forfeited (691 ) 5.90 Balance at December 31, 2018 6,447 $ 5.83 7.6 $ 3,594 Granted 4,978 7.16 Exercised (1,397 ) 2.46 Cancelled/forfeited (1,033 ) 4.93 Balance at December 31, 2019 8,995 $ 7.19 7.6 $ 48,073 Vested and expected to vest as of December 31, 2019 8,995 $ 7.19 7.6 $ 48,073 Exercisable at December 31, 2019 3,485 $ 7.77 5.3 $ 19,968 ( a) The aggregate intrinsic value is calculated as the difference between the stock option exercise price and the closing price of the Company’s common stock of $11.52 per share as of December 31, 2019. The total intrinsic value of stock options exercised during the years ended December 31, 2019 and 2018 were $10.7 million and $8.2 million, respectively. The fair value of each stock option issued was estimated at the date of grant using the Black-Scholes valuation model with the following weighted-average assumptions: Options Employee Stock Purchase Plan Years ended December 31, Years ended December 31, 2019 2018 2019 2018 Expected volatility 81% 80% 105% 78% Expected term (in years) 6.2 6.0 0.5 0.5 Expected dividend yield — — — — Risk-free interest rate 2.1% 2.8% 1.9% 2.3% The weighted-average fair values of options granted during the years ended December 31, 2019 and 2018, were $5.04 and $4.15, respectively. As of December 31, 2019, there was $20.7 million of unrecognized stock-based compensation expense related to stock options that is expected to be recognized over a weighted-average period of 2.8 years. RSUs RSUs are share awards that entitle the holder to receive freely tradable shares of the Company’s common stock upon vesting. The fair value of RSUs is based upon the closing sales price of the Company’s common stock on the grant date. RSUs granted to employees generally vest over a 2–4 year period. The following table summarizes the RSU activity under the Company’s stock plans and related information: (In thousands, except grant date fair value and years) Number of Units (in thousands) Weighted- Average Grant Date Fair Value (in dollars) Weighted- Average Remaining Contractual Term (in years) Balance at December 31, 2017 2,515 $ 3.24 1.6 Granted 1,381 5.94 Vested and released (774 ) 3.46 Forfeited (725 ) 4.28 Balance at December 31, 2018 2,397 $ 9.23 4.8 Granted 250 3.95 Vested and released (663 ) 4.84 Forfeited (863 ) 4.86 Balance at December 31, 2019 1,121 $ 4.59 0.9 The weighted-average grant-date fair value of RSUs granted during the years ended December 31, 2019 and 2018, were $3.95 and $5.94, respectively. During the years ended December 31, 2019 and 2018, total fair value of RSUs vested was $3.4 million and $2.7 million, respectively. The number of RSUs vested includes shares of common stock that the Company withheld on behalf of employees to satisfy the minimum statutory tax withholding requirements. As of December 31, 2019, there was $3.0 million of unrecognized compensation cost related to unvested RSUs that is expected to be recognized over a weighted-average period of 1.5 years. ESPP In July 2014, the Company approved the establishment of the 2014 Employee Stock Purchase Plan (the “ESPP”). The Company reserved 208,833 shares of its common stock for issuance and provided for annual increases in the number of shares available for issuance on the first business day of each fiscal year, beginning in 2015, equal to the lesser of one percent (1%) of the number of the Company’s common stock shares outstanding as of such date or a number of shares as determined by the Company’s board of directors. During the year ended December 31, 2019, 86,405 shares were issued under the ESPP. As of December 31, 2019, a total of 1,875,022 shares of common stock were available for future issuance under the ESPP. As of December 31, 2019, there was $222,000 of unrecognized compensation cost related to the ESPP. Stock-Based Compensation Recognized in the Consolidated Statement of Operations and Comprehensive Loss The following table presents, by operating expense, the Company’s stock-based compensation expense: Years ended December 31, 2019 2018 (In thousands) Research and development $ 3,536 $ 4,820 General and administrative 6,363 8,612 Total share-based compensation expense $ 9,899 $ 13,432 During the years ended December 31, 2019 and 2018, the Company recorded approximately $1.2 million and $4.1 million, respectively of stock‑based compensation expense as a result of the modification of the vesting and exercisability of stock awards associated with the departure of its executives, and directors.

401(k) Savings Plan

401(k) Savings Plan	12 Months Ended
	Dec. 31, 2019
Compensation And Retirement Disclosure [Abstract]
401(k) Savings Plan	11. 401(k) Savings Plan The Company established a defined-contribution savings plan under Section 401(k) of the Code. The 401(k) Plan covers all employees who meet defined minimum age and service requirements, and allows participants to defer a portion of their annual compensation on a pretax basis. The amount of contributions that the Company made to the 401(k) Plan during the year ended December 31, 2019 and 2018 was $0.4 million and $0.4 million, respectively.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes	12. Income Taxes Due to the full valuation allowance, no income tax benefit or expense was recorded for the year ended December 31, 2019. The Company recorded $1.3 million income tax benefit related to the change in the deferred tax liabilities balance due to intangible assets impairment recognized in the third quarter of 2018. The following table presents domestic and foreign components of loss before provision for income taxes: Years ended December 31, 2019 2018 (In thousands) U.S. $ (59,426 ) $ (45,024 ) Foreign (5,060 ) (28,853 ) Loss before income taxes $ (64,486 ) $ (73,877 ) A reconciliation of income tax expense computed at the statutory federal income tax rate of 21% during the years ended December 31, 2019 and 2018 to income taxes as reflected in the financial statements is as follows: Years ended December 31, 2019 2018 (In thousands) Federal income tax expense at statutory rate $ (13,542 ) $ (15,514 ) Stock compensation (1,212 ) (1,512 ) Non-deductible expenses 307 75 Other 298 41 Research and development tax credits (948 ) (1,215 ) Change in valuation allowance 18,312 11,219 Foreign rate differential (212 ) (586 ) State deferred tax adjustment 3,239 — Change in state uncertain tax positions (6,242 ) 6,242 Total tax benefit $ — $ (1,250 ) Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. The following table presents significant components of the Company’s deferred tax assets: As of December 31, 2019 2018 (In thousands) Deferred tax assets: Net operating loss carryforwards $ 53,309 $ 37,247 Accruals, reserve and other 834 827 Stock-based compensation 4,767 4,549 Tax credit carryforwards 6,008 4,161 Property and equipment — 310 Intangibles 24 38 Lease obligation 6,896 — Other 151 122 Total deferred tax assets before valuation allowance 71,989 47,254 Valuation allowance (66,201 ) (47,254 ) Total deferred tax assets 5,788 — Deferred tax liabilities: Property and equipment (1,305 ) — Right-of-use assets (4,483 ) — Total deferred tax liabilities $ (5,788 ) $ — Net deferred tax assets $ — $ — The Company has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets. Based on the Company’s history of operating losses, the Company has concluded that it is more likely than not that the benefit of its deferred tax assets will not be realized. Accordingly, the Company has provided a full valuation allowance for deferred tax assets as of December 31, 2019 and 2018. The valuation allowance increased approximately $18.9 million and $11.8 million during the years ended December 31, 2019 and 2018, respectively. As of December 31, 2019, the Company had U.S. federal net operating losses (“NOLs”) carryforwards of approximately $159.5 million to offset any future federal income. Approximately $56.9 million of NOLs expire at various years beginning with 2036. As of December 31, 2019, the Company also had U.S. state NOL carryforwards of approximately $26.9 million to offset any future state income. U.S. state NOLs expire at various years beginning with 2036. At December 31, 2019, the Company also had approximately $70.1 million of foreign net operating loss carryforwards which may be available to offset future foreign income; these carryforwards do not expire. As of December 31, 2019 , the Company had federal research and development tax credit carryforwards of approximately $4.6 million available to reduce future tax liabilities which expire at various years beginning with 2036. As of December 31, 2019, the Company had state credit carryforwards of approximately $4.6 million available to reduce future tax liabilities which do not expire. Under Section 382 of the Internal Revenue Code of 1986, as amended (Code), the Company’s ability to utilize NOL carryforwards or other tax attributes, such as research tax credits, in any taxable year may be limited if the Company experiences an “ownership change.” Generally, a Section 382 ownership change occurs if there is a cumulative increase of more than 50 percentage points in the stock ownership of one or more stockholders or groups of stockholders who owns at least 5% of a corporation’s stock within a specified testing period. Similar rules may apply under state tax laws. The Company believes that it has experienced ownership changes under Section 382, which will result in limitations in the Company’s ability to utilize NOLs and credits. As a result, the amount of the NOLs and research and development credit carryforwards presented in the Company’s consolidated financial statements are permanently limited and will expire unutilized. Therefore, the Company removed a significant amount of NOLs and credits from its deferred taxe assets. The Company files income tax returns in the U.S. federal, state, and foreign jurisdictions. The federal, state and foreign income tax returns are open under the statute of limitations subject to tax examinations for the tax years ended December 31, 2016 through December 31, 2018. To the extent the Company has tax attribute carryforwards, the tax years in which the attribute was generated may still be adjusted upon examination by the Internal Revenue Service, state or foreign tax authorities to the extent utilized in a future period. The Company has total unrecognized tax benefits as of December 31, 2019 and 2018 of approximately $3.6 million and $8.8 million, respectively. No amount of the unrecognized tax benefits, if recognized, would reduce the Company’s annual effective tax rate because the benefits are in the form of deferred tax assets for which a full valuation allowance has been recorded. The Company does not anticipate a significant change to its unrecognized tax benefits over the next twelve months. A reconciliation of the unrecognized tax benefits is as follows: Years ended December 31, 2019 2018 (In thousands) Unrecognized tax benefits as of the beginning of the year $ 8,805 $ 2,745 Increase (decrease) related to prior year tax provisions (6,242 ) 1,941 Increase related to current year tax provisions 995 4,119 Unrecognized tax benefits as of the end of the year $ 3,558 $ 8,805 The Company recognizes interest and penalties related to uncertain tax positions in income tax expense. As of December 31, 2019, and 2018, the Company had no accrued interest or penalties related to uncertain tax positions and no amounts have been recognized in the Company’s consolidated statements of operations and comprehensive loss. There are no ongoing examinations by taxing authorities at this time.

Net Loss per Share

Net Loss per Share	12 Months Ended
	Dec. 31, 2019
Earnings Per Share [Abstract]
Net Loss per Share	13. Net Loss per Share The following common stock equivalents outstanding at the end of the periods presented were excluded from the calculation of diluted net loss per share for the periods indicated because including them would have had an anti-dilutive effect: As of December 31, 2019 2018 (In thousands) Stock options 8,995 6,447 Restricted stock units 1,121 2,397 ESPP 15 62 Warrants to purchase common stock 90 90 10,221 8,996

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2019
Related Party Transactions [Abstract]
Related Party Transactions	14. Related Party Transactions In May 2019, the Company entered into a common stock purchase agreement with James Scopa, a member of the Board, and Anne Kenner, as Trustees for the James P. Scopa and Anne E. Kenner Family Trust (the “Trust”), pursuant to which the Trust purchased an aggregate of 20,000 shares of the Company’s common stock at a price of $6.71 per share, for an aggregate cash purchase price of $0.1 million.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2019
Subsequent Events [Abstract]
Subsequent Events	15. Subsequent Events In February 2020, the Company sold an aggregate of 10,925,000 shares of its common stock for $140.8 million of net proceeds after deducting underwriting discounts and commissions and estimated offering expenses.

Summary of significant accoun_2

Summary of significant accounting policies (Policies)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Basis of Presentation and Principles of Consolidation	Basis of Presentation and Principles of Consolidation — The Company’s consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”). The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All inter-company transactions and balances have been eliminated in consolidation.
Use of Estimates	Use of Estimates —The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, and the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of income and expenses during the reporting period. The Company bases estimates and assumptions on historical experience when available and on various factors that it believes to be reasonable under the circumstances. The Company evaluates its estimates and assumptions, including those related to research and development expense accruals, stock-based compensation expense, income taxes, fair values of financial instruments, and incremental borrowing rate. The Company’s actual results may differ from these estimates under different assumptions or conditions. There have been no significant changes from the Company’s original estimates in any periods presented.
Foreign Currency Translation	Foreign Currency Translation —The Company’s consolidated financial statements are prepared in U.S. dollars. The Company’s foreign subsidiaries use the Euro and Australian dollar as their functional currencies and maintain their records in their local currencies, except its Ireland subsidiary that uses the U.S. dollar as its functional currency. Assets and liabilities are re-measured at exchange rates in effect at the end of the reporting period for the Company’s French and Australian subsidiaries, and at historical exchange rates for its Irish subsidiary. Equity is measured at historical rates and income and expenses are re-measured at average exchange rates for the reporting period. The resulting foreign currency translation adjustment is recorded in accumulated other comprehensive loss in the consolidated balance sheet. Transactions denominated in foreign currency are translated at exchange rates at the date of transaction with foreign currency gains (losses) recorded in other comprehensive income, net in the consolidated statements of operations and comprehensive loss.
Cash and Cash Equivalents	Cash and Cash Equivalents —The Company considers all highly liquid investments purchased with original maturities of three months or less at the date of purchase to be cash equivalents. Cash and cash equivalents include cash held in banks, money market accounts and highly liquid debt securities. Cash equivalents are stated at fair value.
Restricted Cash	Restricted Cash —Restricted cash primarily consists of cash collateral to letter of credit provided to the landlord in relation to a lease agreement (see Note 5).
Short-Term Investments	Short-Term Investments —All short-term investments, which consist of debt securities and certificates of deposit, have been classified as “available for sale” and are carried at fair value. Unrealized gains and losses, net of any related tax effects, are excluded from earnings and are included in other comprehensive loss and reported as a separate component of stockholders’ equity until realized. Realized gains and losses and declines in value judged to be other than temporary, if any, on available-for-sale securities are included in other income (expense), net in the Company’s consolidated statements of operations and comprehensive loss. The cost of securities sold is based on the specific-identification method. The amortized cost of securities is adjusted for amortization of premiums and accretion of discounts to maturity. Interest on short-term investments is included in other income, net in the Company’s consolidated statements of operations and comprehensive loss. In accordance with the Company’s investment policy, management invests to diversify credit risk and only invests in securities with high credit quality, including U.S. government securities. The Company periodically evaluates whether declines in the fair value of its investments below their cost are other than temporary. The evaluation includes consideration of the cause of the impairment, including the creditworthiness of the security issuers, the number of securities in an unrealized loss position, the severity and duration of the unrealized losses, whether the Company has the intent to sell the securities, and whether it is more likely than not that the Company will be required to sell the securities before the recovery of their amortized cost basis. If the Company determines that the decline in fair value of an investment is below its accounting basis and this decline is other than temporary, the Company would reduce the carrying value of the security it holds and records a loss for the amount of such decline. The Company has not recorded any realized losses or declines in value judged to be other than temporary on its investments.
Segment Reporting	Segment Reporting —The Company operates and manages its business as one reporting and operating segment, which is the business of developing and commercializing gene therapeutics. The Company’s chief executive officer, who is the chief operating decision maker, reviews financial information on an aggregate basis for purposes of allocating resources and evaluating financial performance.
Concentrations of Credit Risk and Other Uncertainties	Concentrations of Credit Risk and Other Uncertainties —Financial instruments that potentially subject the Company to significant concentrations of credit risk consists primarily of cash, cash equivalents and short-term investments. Risks associated with cash, cash equivalents, short-term investments are mitigated by the Company’s investment policy, which limits the Company’s investing to only those marketable securities rated at least A-1/P-1 Short Term Rating and A/A2 Long Term Rating, as determined by independent credit rating agencies. Management believes that the Company is not exposed to significant credit risk. The Company is subject to certain risks and uncertainties, including, but not limited to changes in any of the following areas that the Company believes could have a material adverse effect on future financial position or results of operations: ability to obtain future financing; regulatory approval and market acceptance of, and reimbursement for, the Company’s product candidates; performance of third-party clinical research organizations and manufacturers; development of sales channels; protection of the intellectual property; litigation or claims against the Company based on intellectual property, patent, product, regulatory or other factors; and the Company’s ability to attract and retain employees necessary to support the growth.
Property and Equipment	Property and Equipment —Property and equipment are recorded at cost, net of accumulated depreciation and amortization. Depreciation is recorded using the straight-line method over the estimated useful lives of the assets, generally three to five years. Leasehold improvements are capitalized and amortized over the shorter period of their expected lives or the lease term. Major replacements and improvements are capitalized, while general repairs and maintenance are expensed as incurred.
Valuation of Long-Lived Assets and Purchased Intangible Assets	Valuation of Long-Lived Assets and Purchased Intangible Assets —The Company evaluates the carrying value of amortizable long‑lived assets, whenever events, or changes in business circumstances or the planned use of long‑lived assets indicate that their carrying amounts may not be fully recoverable or that their useful lives are no longer appropriate. If these facts and circumstances exist, the Company assesses for recovery by comparing the carrying values of long‑lived assets with their future undiscounted net cash flows. If the comparison indicates that impairment exists, long‑lived assets are written down to their respective fair values based on discounted cash flows. Significant management judgment is required in the forecasting of future operating results that is used in the preparation of expected undiscounted cash flows. If management’s assumptions about future operating results were to change as a result of events or circumstances, the Company may be required to record an impairment loss on these assets. There were no impairment indicators noted for the Company’s amortizable long-lived assets, fixed assets, in the year ended December 31, 2019. The Company also evaluates the carrying value of intangible asset (not subject to amortization) related to in‑process research and development (“IPR&D”) asset, which is considered to be indefinite‑lived until the completion or abandonment of the associated research and development efforts. Accordingly, amortization of the IPR&D assets will not occur until the product reaches commercialization. During the period the intangible asset is considered indefinite‑lived, it will be tested for impairment on an annual basis, as well as between annual tests if the Company becomes aware of any events occurring or changes in circumstances that would indicate that the fair value of the IPR&D asset is less than its carrying amount. If and when development is complete, which generally occurs when regulatory approval to market the product is obtained, the associated IPR&D asset would be deemed definite‑lived and would then be amortized based on its estimated useful life at that point in time based on respective patent term. If a potential impairment exists, an impairment loss is measured as the excess of the asset’s carrying value over its fair value. During the year ended December 31, 2018, the Company recorded an impairment charge of $5.0 million related to its intangible assets.
Revenue Recognition	Revenue Recognition —The Company has primarily generated revenue through license, research and collaboration arrangements with its strategic partners. Under Topic 606, the Company recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the Company expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that the Company determines are within the scope of ASC 606, the Company performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the Company satisfies a performance obligation. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. The Company’s license and collaboration arrangements with Editas Medicine, Inc. (“Editas”) and GenSight Biologics (“GenSight”) are within the scope of Topic 606. Collaboration Agreement with Editas — Under Topic 606, the transaction price at contract inception was determined to be $1.0 million, which was related to the non-refundable upfront payment for license and research services. The transaction price of $1.0 million at contract inception was allocated to a single performance obligation. During the year ended December 31, 2018, the Company recognized revenue of $1.5 million associated with the Editas collaboration agreement. The remaining performance obligations for Editas were completed during 2018. During the year ended December 31, 2019, the Company had no recognized revenue from the Editas collaboration agreement. There was no outstanding deferred revenue associated with Editas as of December 31, 2019 and 2018. License Agreement with GenSight — On February 2014, the Company entered into an agreement with GenSight, where the Company granted GenSight a non-exclusive license to its proprietary AAV.7m8 vector. Under the agreement, the Company is eligible to receive development, regulatory and commercial milestones. Also, the Company is eligible to receive low to mid-single digit royalties on sales of GenSight’s licensed products. During the years ended December 31, 2019 and 2018, GenSight achieved clinical development milestones pursuant to the agreement. This milestone was previously constrained under Topic 606. The Company earned milestone payments of $250,000 and $150,000, which were recognized as revenue for the years ended December 31, 2019 and 2018, respectively.
Research and Development Expenses	Research and Development Expenses —Research and development expenses are charged to expense as incurred. Research and development expenses include primarily personnel-related costs, stock-based compensation expense, laboratory supplies, consulting costs, external contract research and development expenses, including expenses incurred under agreements with CROs, the cost of acquiring, developing and manufacturing clinical trial materials, and overhead expenses, such as rent, equipment depreciation, insurance and utilities. Advance payments for goods or services for future research and development activities are deferred and expensed as the goods are delivered or the related services are performed. The Company estimates preclinical studies and clinical trial expenses based on the services performed pursuant to contracts with research institutions and clinical research organizations that conduct and manage preclinical studies and clinical trials on the Company’s behalf. In accruing service fees, the Company estimates the time period over which services will be performed and the level of effort to be expended in each period. These estimates are based on communications with the third-party service providers and the Company’s estimates of accrued expenses and on information available at each balance sheet date. If the actual timing of the performance of services or the level of effort varies from the estimate, the Company will adjust the accrual accordingly. There have been no significant changes from the Company’s original estimates in any of the periods presented.
Fair Value Measurements	Fair Value Measurements —Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. The carrying amounts of the Company’s financial instruments, including cash equivalents, prepaid and other current assets, accounts payable, accrued expenses and other current liabilities approximate their fair values due to their short-term maturities. Refer to Note 3 for the methodologies and assumptions used in valuing financial instruments.
Stock-based Compensation Expense	Stock-based Compensation Expense —Stock-based compensation expense related to stock awards to employees is measured at fair value of the award on the date of the grant. The Company estimates the grant-date fair value, and the resulting stock-based compensation expense, using the Black-Scholes valuation model for stock options and using intrinsic value, which is the closing price of its common stock on the date of the grant, for the restricted stock units (“RSUs”). The fair value of the award that is ultimately expected to vest is recognized as expense on a straight-line basis over the requisite service period, which is generally the vesting period. The Black-Scholes valuation model requires the use of following assumptions: Expected Term —The expected term assumption represents the period that the Company’s stock-based awards are expected to be outstanding and is determined using the simplified method. Expected Volatility —Expected volatility is estimated using a weighing of comparable public companies’ volatility for similar terms and the Company’s historical volatility. Expected Dividend —The Black-Scholes valuation model calls for a single expected dividend yield as an input. The Company has never paid dividends and has no plans to pay dividends. Risk-Free Interest Rate —The risk-free interest rate is based on the U.S. Treasury zero-coupon issues in effect at the time of grant for periods corresponding with the expected term of option.
Income Taxes	Income Taxes —The Company accounts for income taxes using the asset and liability method. The Company recognizes deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements or tax returns. Deferred tax assets and liabilities are determined based on the difference between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. In evaluating the ability to recover its deferred income tax assets, the Company considers all available positive and negative evidence, including its operating results, ongoing tax planning and forecasts of future taxable income on a jurisdiction-by-jurisdiction basis. In the event the Company determines that it would be able to realize its deferred income tax assets in the future in excess of their net recorded amount, it would make an adjustment to the valuation allowance that would reduce the provision for income taxes. Conversely, in the event that all or part of the net deferred tax assets are determined not to be realizable in the future, an adjustment to the valuation allowance would be charged to earnings in the period when such determination is made. As of December 31, 2019 and 2018, the Company has recorded a full valuation allowance on its deferred tax assets. Tax benefits related to uncertain tax positions are recognized when it is more likely than not that a tax position will be sustained upon examination. Interest and penalties related to unrecognized tax liabilities are included within the provision for income tax.
Comprehensive Loss	Comprehensive Loss —Comprehensive loss comprises net loss and other comprehensive income. Other comprehensive income consists of foreign currency translation adjustments related to translation of the financial statements of the Company’s Australia and France subsidiaries and unrealized gain on marketable securities. The Company did not record reclassifications from other comprehensive income (loss) to the income (loss) during the years ended December 31, 2019 and 2018.
Basic and Diluted Net Loss Per Share	Basic and Diluted Net Loss Per Share — Basic net loss per share is calculated by dividing the net loss by the weighted-average number of shares of common stock outstanding for the period. Diluted net loss per share is computed by giving effect to all potential dilutive common stock equivalents outstanding for the period using the treasury stock method. Outstanding stock options, restricted stock units (“RSUs”), employee stock purchase plan (“ESPP”) and warrants are considered to be common stock equivalents and are only included in the calculation of diluted net loss per share when their effect is dilutive.
Leases	Recently Adopted Accounting Pronouncements Leases The Company adopted Accounting Standards Update (ASU) No. 2016-02, Leases (Topic 842) (“Topic 842”) on January 1, 2019. For its long-term operating leases, the Company recognizes a right-of-use asset and a lease liability on its consolidated balance sheets. The Company adopted the new standard using the modified retrospective approach and, upon adoption, recorded a lease liability of $24.7 million, and a right‑to‑use asset of $23.1 million, and made no adjustment to the accumulated deficit. In connection with the adoption of the lease standard, the Company also derecognized deferred rent of $1.5 million. The adoption of Topic 842 did not have an impact on the consolidated statement of operations. The lease liability is determined as the present value of future lease payments using an estimated rate of interest that the Company would pay to borrow equivalent funds on a collateralized basis at the lease commencement date. In order to estimate the incremental borrowing rate, management estimated its credit rating, adjusted the credit rating for the nature of the collateral, and benchmarked the borrowing rate against observable yields on comparable securities with a similar term. As of the adoption date, the Company estimated the incremental borrowing rate to be 8.5%. The Company based the right-of-use asset on the liability adjusted for any prepaid or deferred rent. The Company determined the lease term at the commencement date by considering whether renewal options and termination options are reasonably assured of exercise. Rent expense for the operating lease is recognized on a straight-line basis over the lease term and is included in operating expenses on the statements of operations and comprehensive loss. Variable lease payments include lease operating expenses. The Company elected the practical expedients permitted under Topic 842, which among other things, allowed the Company to carry forward the historical lease classification of those leases in place as of January 1, 2019. The Company elected to exclude from its consolidated balance sheets recognition of leases having a term of 12 months or less (short-term leases) and elected to not separate lease components and non-lease components for its long-term real-estate leases.
Accounting Standard Update Recently Adopted	Share-based payment to nonemployees In June 2018, the FASB issued ASU 2018-07, “Compensation – Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting” (“Topic 718”) that expands the scope of Topic 718 to include share-based payment transactions for acquiring goods and services from nonemployees. The Company adopted ASU 2018–07 on January 1, 2019 and the impact of the adoption resulted in lower stock-based compensation of $1.4 million during the year ended December 31, 2019. Under the new standard, our share-based payment transactions with non-employees have a fixed measurement and are not remeasured over the vesting period.

Fair Value Measurements and F_2

Fair Value Measurements and Fair Value of Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Summary of Cash Equivalents and Short-term Investments	The following is a summary of the Company’s cash equivalents and short-term investments (in thousands): December 31, 2019 Amortized Cost Basis Unrealized Gains Unrealized Loses Estimated Fair Value Level 1 Money market funds $ 15,056 $ — $ — $ 15,056 Level 2 U.S. government and agency securities 37,974 14 (2 ) 37,986 Commercial paper 87,983 8 (8 ) 87,983 Corporate bonds 10,495 6 — 10,501 Total cash equivalents and short-term investments 151,508 28 (10 ) 151,526 Less: Cash equivalents (51,391 ) — 3 (51,388 ) Total short-term investments $ 100,117 $ 28 $ (7 ) $ 100,138 December 31, 2018 Amortized Cost Basis Unrealized Gains Unrealized Loses Estimated Fair Value Level 1 Money market funds $ 126 $ — $ — $ 126 Level 2 U.S. government and agency securities 25,792 1 (4 ) 25,789 Commercial paper 147,606 — — 147,606 Corporate bonds 27,778 5 (17 ) 27,766 Certificates of deposit 1,420 — — 1,420 Total cash equivalents and short-term investments 202,722 6 (21 ) 202,707 Less: Cash equivalents (152,577 ) — — (152,577 ) Total short-term investments $ 50,145 $ 6 $ (21 ) $ 50,130

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2019
Leases [Abstract]
Schedule of Undiscounted Future Lease Payments under Operating Lease	The undiscounted future non-cancellable lease payments under the Company’s operating leases as of December 31, 2019 is as follows: Years ending December 31, (In thousands) 2020 $ 4,221 2021 4,683 2022 4,846 2023 5,016 2024 5,191 Thereafter 23,646 Total undiscounted lease payments 47,603 Less: Present value adjustments (15,355 ) Total $ 32,248

Balance Sheet Components (Table

Balance Sheet Components (Tables)	12 Months Ended
	Dec. 31, 2019
Balance Sheet Related Disclosures [Abstract]
Schedule of Property and Equipment, Net	Property and equipment, net consists of the following: December 31, 2019 2018 (In thousands) Computer equipment and software $ 752 $ 646 Laboratory equipment 6,291 5,470 Furniture and fixtures 678 678 Leasehold improvements 1,602 1,602 Construction in progress 23,553 1,612 Total property and equipment 32,876 10,008 Less accumulated depreciation and amortization (7,992 ) (6,422 ) Property and equipment, net $ 24,884 $ 3,586
Schedule of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consist of the following: December 31, 2019 2018 (In thousands) Compensation expense $ 4,055 $ 2,944 Accrued professional fees 2,607 2,291 Accrued preclinical costs 1,002 289 Accrued clinical and process development costs 971 1,561 Other 2,636 1,699 Total accrued expenses and other current liabilities $ 11,271 $ 8,784

Common Stock Warrants (Tables)

Common Stock Warrants (Tables)	12 Months Ended
	Dec. 31, 2019
Warrants And Rights Note Disclosure [Abstract]
Outstanding Warrants to Purchase Common Stock	The table below represents the outstanding warrants to purchase common stock as of December 31, 2019 and 2018: Issue Date Expiration Date Number of Warrant Shares Outstanding and Exercisable Exercise Price Per Share 12/31/2015 10/15/2020 40,000 $ 10.51 9/28/2017 9/29/2022 40,000 $ 3.65 8/4/2016 8/3/2021 10,000 $ 4.33 90,000

Stock Plans (Tables)

Stock Plans (Tables)	12 Months Ended
	Dec. 31, 2019
Schedule of Fair Value of Option Issued Valuation Assumptions	The fair value of each stock option issued was estimated at the date of grant using the Black-Scholes valuation model with the following weighted-average assumptions: Options Employee Stock Purchase Plan Years ended December 31, Years ended December 31, 2019 2018 2019 2018 Expected volatility 81% 80% 105% 78% Expected term (in years) 6.2 6.0 0.5 0.5 Expected dividend yield — — — — Risk-free interest rate 2.1% 2.8% 1.9% 2.3%
Summary of Restricted Stock Units Activity	The following table summarizes the RSU activity under the Company’s stock plans and related information: (In thousands, except grant date fair value and years) Number of Units (in thousands) Weighted- Average Grant Date Fair Value (in dollars) Weighted- Average Remaining Contractual Term (in years) Balance at December 31, 2017 2,515 $ 3.24 1.6 Granted 1,381 5.94 Vested and released (774 ) 3.46 Forfeited (725 ) 4.28 Balance at December 31, 2018 2,397 $ 9.23 4.8 Granted 250 3.95 Vested and released (663 ) 4.84 Forfeited (863 ) 4.86 Balance at December 31, 2019 1,121 $ 4.59 0.9
Stock-Based Compensation Expense	The following table presents, by operating expense, the Company’s stock-based compensation expense: Years ended December 31, 2019 2018 (In thousands) Research and development $ 3,536 $ 4,820 General and administrative 6,363 8,612 Total share-based compensation expense $ 9,899 $ 13,432
2006 and 2014 Equity Incentive Plan [Member]
Summary of Stock Options Activity	The following table summarizes stock option activity under the Company’s stock plans and related information: (In thousands, except exercise prices and years) Options Outstanding Weighted- Average Exercise Price Weighted- Average Remaining Contract Life (in years) Aggregate Intrinsic Value (a) Balance at December 31, 2017 6,695 $ 4.51 7.4 $ 9,539 Granted 2,049 5.94 Exercised (1,606 ) 0.43 Cancelled/forfeited (691 ) 5.90 Balance at December 31, 2018 6,447 $ 5.83 7.6 $ 3,594 Granted 4,978 7.16 Exercised (1,397 ) 2.46 Cancelled/forfeited (1,033 ) 4.93 Balance at December 31, 2019 8,995 $ 7.19 7.6 $ 48,073 Vested and expected to vest as of December 31, 2019 8,995 $ 7.19 7.6 $ 48,073 Exercisable at December 31, 2019 3,485 $ 7.77 5.3 $ 19,968 ( a) The aggregate intrinsic value is calculated as the difference between the stock option exercise price and the closing price of the Company’s common stock of $11.52 per share as of December 31, 2019.

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Schedule of Components of Loss Before Income Taxes	The following table presents domestic and foreign components of loss before provision for income taxes: Years ended December 31, 2019 2018 (In thousands) U.S. $ (59,426 ) $ (45,024 ) Foreign (5,060 ) (28,853 ) Loss before income taxes $ (64,486 ) $ (73,877 )
Schedule of Reconciliation of Income Tax Expense Computed Statutory Federal Income Tax and Financial Statements	A reconciliation of income tax expense computed at the statutory federal income tax rate of 21% during the years ended December 31, 2019 and 2018 to income taxes as reflected in the financial statements is as follows: Years ended December 31, 2019 2018 (In thousands) Federal income tax expense at statutory rate $ (13,542 ) $ (15,514 ) Stock compensation (1,212 ) (1,512 ) Non-deductible expenses 307 75 Other 298 41 Research and development tax credits (948 ) (1,215 ) Change in valuation allowance 18,312 11,219 Foreign rate differential (212 ) (586 ) State deferred tax adjustment 3,239 — Change in state uncertain tax positions (6,242 ) 6,242 Total tax benefit $ — $ (1,250 )
Schedule of Deferred Tax Assets	The following table presents significant components of the Company’s deferred tax assets: As of December 31, 2019 2018 (In thousands) Deferred tax assets: Net operating loss carryforwards $ 53,309 $ 37,247 Accruals, reserve and other 834 827 Stock-based compensation 4,767 4,549 Tax credit carryforwards 6,008 4,161 Property and equipment — 310 Intangibles 24 38 Lease obligation 6,896 — Other 151 122 Total deferred tax assets before valuation allowance 71,989 47,254 Valuation allowance (66,201 ) (47,254 ) Total deferred tax assets 5,788 — Deferred tax liabilities: Property and equipment (1,305 ) — Right-of-use assets (4,483 ) — Total deferred tax liabilities $ (5,788 ) $ — Net deferred tax assets $ — $ —
Schedule of Unrecognized Tax Benefits	A reconciliation of the unrecognized tax benefits is as follows: Years ended December 31, 2019 2018 (In thousands) Unrecognized tax benefits as of the beginning of the year $ 8,805 $ 2,745 Increase (decrease) related to prior year tax provisions (6,242 ) 1,941 Increase related to current year tax provisions 995 4,119 Unrecognized tax benefits as of the end of the year $ 3,558 $ 8,805

Net Loss per Share (Tables)

Net Loss per Share (Tables)	12 Months Ended
	Dec. 31, 2019
Earnings Per Share [Abstract]
Schedule of Antidilutive Common Stock Equivalents Excluded from Calculation of Diluted Net Loss Per Share	The following common stock equivalents outstanding at the end of the periods presented were excluded from the calculation of diluted net loss per share for the periods indicated because including them would have had an anti-dilutive effect: As of December 31, 2019 2018 (In thousands) Stock options 8,995 6,447 Restricted stock units 1,121 2,397 ESPP 15 62 Warrants to purchase common stock 90 90 10,221 8,996

Description of the Business - A

Description of the Business - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Date of incorporation	Jul. 17, 2006
Accumulated deficit	$ (385,029)	$ (320,543)

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Detail)	1 Months Ended		12 Months Ended
	Feb. 28, 2018USD ($)	Aug. 31, 2016USD ($)	Dec. 31, 2019USD ($)Segment	Dec. 31, 2018USD ($)	Jan. 01, 2019USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of reportable segments | Segment			1
Number of operating segments | Segment			1
Impairment losses of amortizable long-lived assets			$ 0
Collaboration and license revenue			$ 250,000	$ 1,612,000
Type of Revenue [Extensible List]			us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Right-to-use asset			$ 20,963,000
Lease liability			32,248,000
Stock-based compensation			(9,899,000)	$ (13,432,000)
ASU No. 2016-2, Leases [Member]
Summary Of Significant Accounting Policies [Line Items]
Right-to-use asset					$ 23,100,000
Lease liability					24,700,000
Adjustment to accumulated deficit					$ 0
Estimated incremental borrowing rate					8.50%
ASU No. 2016-2, Leases [Member] | Restatement Adjustment [Member]
Summary Of Significant Accounting Policies [Line Items]
Derecognized deferred rent					$ 1,500,000
ASU 2018-07 [Member] | Restatement Adjustment [Member]
Summary Of Significant Accounting Policies [Line Items]
Stock-based compensation			1,400,000
Editas Medicine Inc [Member]
Summary Of Significant Accounting Policies [Line Items]
Collaboration and license revenue			$ 0	$ 1,500,000
Type of Revenue [Extensible List]			us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Editas Medicine Inc [Member] | Accounting Standards Update 2014-09 [Member]
Summary Of Significant Accounting Policies [Line Items]
Initial payments received	$ 500,000
Deferred revenue			$ 0	$ 0
Collaboration and license revenue			$ 0	$ 1,500,000
Type of Revenue [Extensible List]			us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Editas Medicine Inc [Member] | Upfront Payment Arrangement [Member] | Accounting Standards Update 2014-09 [Member]
Summary Of Significant Accounting Policies [Line Items]
Initial payments received		$ 1,000,000
Deferred revenue		$ 1,000,000
GenSight Biologics [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Summary Of Significant Accounting Policies [Line Items]
Collaboration and license revenue			$ 250,000	$ 150,000
Type of Revenue [Extensible List]			us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
GenSight Biologics [Member] | License Agreement [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Summary Of Significant Accounting Policies [Line Items]
Collaboration and license revenue			$ 250,000	$ 150,000
IPR&D [Member]
Summary Of Significant Accounting Policies [Line Items]
Impairment of intangible assets				$ 5,000,000
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives of assets			3 years
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives of assets			5 years

Fair Value Measurements and F_3

Fair Value Measurements and Fair Value of Financial Instruments - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Available For Sale Securities [Abstract]
Liabilities transferred within Level 3	$ 0	$ 0
Marketable securities other-than-temporarily impaired	$ 0
Remaining maturity period of investments	1 year

Fair Value Measurements and F_4

Fair Value Measurements and Fair Value of Financial Instruments - Summary of Cash Equivalents and Short-term Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	$ 100,117	$ 50,145
Unrealized Gains	28	6
Unrealized Loses	(7)	(21)
Estimated Fair Value	100,138	50,130
Less: Cash Equivalents, Amortized Cost Basis	(51,391)	(152,577)
Less: Cash Equivalents, Unrealized Gains	0	0
Less: Cash Equivalents, Unrealized Loses	3	0
Less: Cash Equivalents, Estimated Fair Value	(51,388)	(152,577)
Money Market Funds [Member] | Quoted Prices in Active Markets (Level 1) [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	15,056	126
Estimated Fair Value	15,056	126
U.S. Government Agency Securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	37,974	25,792
Unrealized Gains	14	1
Unrealized Loses	(2)	(4)
Estimated Fair Value	37,986	25,789
Commercial Paper [Member] | Significant Other Observable Inputs (Level 2) [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	87,983	147,606
Unrealized Gains	8
Unrealized Loses	(8)
Estimated Fair Value	87,983	147,606
Certificates of Deposit [Member] | Significant Other Observable Inputs (Level 2) [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis		1,420
Estimated Fair Value		1,420
Corporate Bonds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	10,495	27,778
Unrealized Gains	6	5
Unrealized Loses		(17)
Estimated Fair Value	10,501	27,766
Total Cash Equivalents and Short-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	151,508	202,722
Unrealized Gains	28	6
Unrealized Loses	(10)	(21)
Estimated Fair Value	$ 151,526	$ 202,707

Revenue - Additional Informatio

Revenue - Additional Information (Detail) - USD ($)	1 Months Ended		12 Months Ended
	Feb. 28, 2018	Aug. 31, 2016	Dec. 31, 2019	Dec. 31, 2018
License Agreement [Line Items]
Revenue recognized			$ 250,000	$ 1,612,000
Type of Revenue [Extensible List]			us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Editas Medicine Inc [Member]
License Agreement [Line Items]
Revenue recognized			$ 0	$ 1,500,000
Type of Revenue [Extensible List]			us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Deferred revenue			$ 0	$ 0
Editas Medicine Inc [Member] | Topic 606 [Member]
License Agreement [Line Items]
Collaboration, option and license agreement fee receivable per indication		$ 1,500,000
Non-refundable upfront payment received		$ 1,000,000
Initial payments received	$ 500,000
Revenue recognized			$ 0	$ 1,500,000
Type of Revenue [Extensible List]			us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
GenSight Biologics [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
License Agreement [Line Items]
Revenue recognized			$ 250,000	$ 150,000
Type of Revenue [Extensible List]			us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember

Leases - Additional Information

Leases - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)ft²	Dec. 31, 2018USD ($)	Jan. 01, 2019USD ($)
Lessee Lease Description [Line Items]
Restricted cash	$ 999	$ 999
Operating lease right-of-use assets	20,963
Lease liability	32,248
Rent expense	6,500	$ 3,300
Variable lease costs	$ 1,600
ASU No. 2016-2, Leases [Member]
Lessee Lease Description [Line Items]
Operating lease right-of-use assets			$ 23,100
Lease liability			$ 24,700
Estimated incremental borrowing rate			8.50%
Redwood City [Member]
Lessee Lease Description [Line Items]
Lease entered date	Jun. 30, 2018
Lease, area of land | ft²	81,000
Lease term	10 years
Lease renewal term	7 years
Lease description	The lease term is 10 years beginning September 2018 through February 2029 with two options to extend the lease term for a period of seven years each.
Lease, option to extend	true
Lease incentive allowance	$ 8,100
Restricted cash	$ 1,000
Menlo Park [Member]
Lessee Lease Description [Line Items]
Lease, option to extend	false
Lease expiration date	May 8, 2020
Letter of Credit [Member] | Redwood City [Member]
Lessee Lease Description [Line Items]
Security deposit	$ 1,000

Leases - Schedule of Undiscount

Leases - Schedule of Undiscounted Future Lease Payments under Operating Lease (Detail) $ in Thousands	Dec. 31, 2019USD ($)
Leases [Abstract]
2020	$ 4,221
2021	4,683
2022	4,846
2023	5,016
2024	5,191
Thereafter	23,646
Total undiscounted lease payments	47,603
Less: Present value adjustments	(15,355)
Lease liability	$ 32,248

Balance Sheet Components - Sche

Balance Sheet Components - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Total property and equipment	$ 32,876	$ 10,008
Less accumulated depreciation and amortization	(7,992)	(6,422)
Property and equipment, net	24,884	3,586
Computer Equipment and Software [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	752	646
Laboratory Equipment [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	6,291	5,470
Furniture and Fixtures [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	678	678
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	1,602	1,602
Construction in Progress [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	$ 23,553	$ 1,612

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Abstract]
Construction in progress	$ 23,600	$ 1,600
Depreciation and amortization expense	$ 1,573	$ 1,750

Balance Sheet Components - Sc_2

Balance Sheet Components - Schedule of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Accrued Expenses And Other Current Liabilities [Abstract]
Compensation expense	$ 4,055	$ 2,944
Accrued professional fees	2,607	2,291
Accrued preclinical costs	1,002	289
Accrued clinical and process development costs	971	1,561
Other	2,636	1,699
Total accrued expenses and other current liabilities	$ 11,271	$ 8,784

Financing Arrangements - Additi

Financing Arrangements - Additional Information (Detail) - BPI France [Member] $ in Millions	12 Months Ended
	Dec. 31, 2019EUR (€)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2016EUR (€)	Aug. 31, 2015EUR (€)
Debt Instrument [Line Items]
Interest free conditional advance, maximum borrowing capacity | €					€ 800,000
Interest free conditional advance		$ 0.2	$ 0.3	€ 500,000
Interest free conditional advance, frequency of payments	Quarterly
Interest free conditional advance, periodic payment | €	€ 25,000
Interest free conditional advance, beginning date of periodic payment	Sep. 30, 2017
Interest free conditional advance, ending date of periodic payment	Jun. 30, 2022
Interest free conditional advance, imputed interest rate		7.00%
Other Noncurrent Liabilities [Member]
Debt Instrument [Line Items]
Interest free conditional advance | $		$ 0.1	0.2
Accrued Expenses and Other Current Liabilities [Member]
Debt Instrument [Line Items]
Interest free conditional advance | $		$ 0.1	$ 0.1

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail)	1 Months Ended		12 Months Ended
	Jun. 30, 2019USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2019USD ($)Claim	Dec. 31, 2018USD ($)Claim
Other Commitments [Line Items]
Accrued royalties				$ 0
Type of Cost, Good or Service [Extensible List]			us-gaap:MaintenanceMember	us-gaap:MaintenanceMember
Claims paid to date related to indemnification issues			$ 0	$ 0
Number of claims to date | Claim			0	0
Accruals or expenses related to indemnification issues			$ 0	$ 0
Cornell University [Member] | Master Service Agreement [Member]
Other Commitments [Line Items]
Service purchase commitment amount		$ 13,300,000
Service expenses payment period		4 years
Payment for settlement agreement	$ 2,000,000
Settlement agreement current period expense			$ 0

Common Stock Warrants - Outstan

Common Stock Warrants - Outstanding Warrants to Purchase Common Stock (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Class Of Warrant Or Right [Line Items]
Number of Warrant Shares Outstanding and Exercisable	90,000	90,000
Warrants Issued on December 31, 2015 [Member]
Class Of Warrant Or Right [Line Items]
Issue Date	Dec. 31, 2015	Dec. 31, 2015
Expiration Date	Oct. 15, 2020	Oct. 15, 2020
Number of Warrant Shares Outstanding and Exercisable	40,000	40,000
Exercise Price Per Share	$ 10.51	$ 10.51
Warrants Issued on September 28, 2017 [Member]
Class Of Warrant Or Right [Line Items]
Issue Date	Sep. 28, 2017	Sep. 28, 2017
Expiration Date	Sep. 29, 2022	Sep. 29, 2022
Number of Warrant Shares Outstanding and Exercisable	40,000	40,000
Exercise Price Per Share	$ 3.65	$ 3.65
Warrants Issued on August 4, 2016 [Member]
Class Of Warrant Or Right [Line Items]
Issue Date	Aug. 4, 2016	Aug. 4, 2016
Expiration Date	Aug. 3, 2021	Aug. 3, 2021
Number of Warrant Shares Outstanding and Exercisable	10,000	10,000
Exercise Price Per Share	$ 4.33	$ 4.33

Common Stock Warrants - Additio

Common Stock Warrants - Additional Information (Detail) - The Alpha-1 Project, Inc. [Member] - Common Stock [Member] - shares	Feb. 29, 2020	Jul. 31, 2016
Class Of Warrant Or Right [Line Items]
Warrants issued to purchase shares of common stock		10,000
Subsequent Event [Member]
Class Of Warrant Or Right [Line Items]
Common stock issued upon exercise of warrants	7,250

Stock Plans - Additional Inform

Stock Plans - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
	Jul. 31, 2014	Dec. 31, 2019	Dec. 31, 2018	Oct. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total intrinsic value of stock options exercised		$ 10,700,000	$ 8,200,000
Weighted-average fair values of options granted		$ 5.04	$ 4.15
Unrecognized stock-based compensation expense related to awards		$ 20,700,000
Unrecognized stock-based compensation, weighted-average period		2 years 9 months 18 days
One time share based payment charge related to cancellation of unvested stock option of CEO and directors		$ 1,200,000	$ 4,100,000
Plans [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares authorized for issuance		24,372,087
Shares available for future grants		4,369,053
Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation, weighted-average period		1 year 6 months
Weighted-average grant date fair value of RSUs granted		$ 3.95	$ 5.94
Total fair values of RSUs vested		$ 3,400,000	$ 2,700,000
Unrecognized compensation cost		$ 3,000,000
Restricted Stock Units [Member] | Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Awards granted to employees and non-employees vesting period		4 years
Restricted Stock Units [Member] | Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Awards granted to employees and non-employees vesting period		2 years
2014 Equity Incentive Award Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of annual increase in number of shares available for future issuance	4.00%
2017 Inducement Plan [Member] | Stock Options and Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares available for future grant				600,000
2014 Plan And Inducement Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options granted description		Stock options under the 2014 Plan and the Inducement Plan may be granted for periods of up to 10 years and at prices no less than 100% of the estimated fair value of the shares on the date of grant as determined by the board of directors, provided, however, that the exercise price of an ISO and NSO granted to a 10% stockholder may not be less than 110% of the estimated fair value of the shares on the date of grant.
Awards granted to employees and non-employees vesting period		4 years
2014 Plan And Inducement Plan [Member] | Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options granted period		10 years
2014 Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares available for future grant	208,833
Shares available for future grants		1,875,022
Unrecognized compensation cost		$ 222,000
Percentage increase in shares issued	1.00%
Common stock, shares issued		86,405

Stock Plans - Summary of Stock

Stock Plans - Summary of Stock Options Activity (Detail) - 2006 Equity Incentive Plan [Member] - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Options Outstanding [Roll Forward]
Options Outstanding, Beginning Balance	6,447	6,695
Options Outstanding, Granted	4,978	2,049
Options Outstanding, Exercised	(1,397)	(1,606)
Options Outstanding, Cancelled/forfeited	(1,033)	(691)
Options Outstanding, Ending Balance	8,995	6,447	6,695
Options Outstanding, Vested and expected to vest	8,995
Options Outstanding, Exercisable	3,485
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted-Average Exercise Price, Beginning Balance	$ 5.83	$ 4.51
Weighted-Average Exercise Price, Granted	7.16	5.94
Weighted-Average Exercise Price, Exercised	2.46	0.43
Weighted-Average Exercise Price, Cancelled/forfeited	4.93	5.90
Weighted-Average Exercise Price, Ending Balance	7.19	$ 5.83	$ 4.51
Weighted-Average Exercise Price, Vested and expected to vest	7.19
Weighted-Average Exercise Price, Exercisable	$ 7.77
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted-Average Remaining Contractual Life (In years)	7 years 7 months 6 days	7 years 7 months 6 days	7 years 4 months 24 days
Weighted-Average Remaining Contractual Life (In years), Vested and expected to vest	7 years 7 months 6 days
Weighted-Average Remaining Contractual Life (In years), Exercisable	5 years 3 months 18 days
Aggregate Intrinsic Value, Options outstanding	$ 48,073	$ 3,594	$ 9,539
Aggregate Intrinsic Value, Vested and expected to vest	48,073
Aggregate Intrinsic Value, Exercisable	$ 19,968

Stock Plans - Summary of Stoc_2

Stock Plans - Summary of Stock Options Activity (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2019$ / shares
Equity [Abstract]
Aggregate intrinsic value of option per share	$ 11.52

Stock Plans - Schedule of Stock

Stock Plans - Schedule of Stock Purchase Plan Valuation Assumptions (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Employee Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility	81.00%	80.00%
Expected term (in years)	6 years 2 months 12 days	6 years
Risk-free interest rate	2.10%	2.80%
Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility	105.00%	78.00%
Expected term (in years)	6 months	6 months
Risk-free interest rate	1.90%	2.30%

Stock Plans - Summary of Restri

Stock Plans - Summary of Restricted Stock Units Activity (Detail) - Restricted Stock Units [Member] - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Units, Beginning Balance	2,397	2,515
Number of Units, Granted	250	1,381
Number of Units, Vested and released	(663)	(774)
Number of Units, Forfeited	(863)	(725)
Number of Units, Ending Balance	1,121	2,397	2,515
Weighted-Average Grant-Date Fair Value, Beginning Balance	$ 9.23	$ 3.24
Weighted-Average Grant-Date Fair Value, Granted	3.95	5.94
Weighted-Average Grant-Date Fair Value, Vested and released	4.84	3.46
Weighted-Average Grant-Date Fair Value, Forfeited	4.86	4.28
Weighted-Average Grant-Date Fair Value, Ending Balance	$ 4.59	$ 9.23	$ 3.24
Weighted-Average Remaining Contractual Term (In years)	10 months 24 days	4 years 9 months 18 days	1 year 7 months 6 days

Stock Plans - Stock-Based Compe

Stock Plans - Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total share-based compensation expense	$ 9,899	$ 13,432
Research and Development [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total share-based compensation expense	3,536	4,820
General and Administrative [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total share-based compensation expense	$ 6,363	$ 8,612

401(k) Savings Plan - Additiona

401(k) Savings Plan - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Compensation And Retirement Disclosure [Abstract]
Contribution by company	$ 0.4	$ 0.4

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Line Items]
Income tax benefit or expense	$ 1,300,000	$ 0	$ 1,250,000
Statutory federal income tax rate		21.00%	21.00%
Increase (decrease) in valuation allowance due to net operating loss		$ 18,900,000	$ 11,800,000
Unrecognized tax benefits		3,558,000	8,805,000	$ 2,745,000
Unrecognized tax benefits, if recognized would effective annual tax rate		0
Accrued interest or penalties related to uncertain tax positions		$ 0	0
Interest or penalties recognized			$ 0	$ 0
Minimum [Member]
Income Taxes [Line Items]
Tax examinations, year under examination		2016
Maximum [Member]
Income Taxes [Line Items]
Tax examinations, year under examination		2018
Domestic Tax Authority [Member]
Income Taxes [Line Items]
NOL carryforwards		$ 159,500,000
NOL carryforwards subject to expiration		$ 56,900,000
NOL carryforwards expiration		expire at various years beginning with 2036
Domestic Tax Authority [Member] | Research Tax Credit Carryforward [Member]
Income Taxes [Line Items]
Tax credit carryforwards		$ 4,600,000
Tax credit carryforwards expiration		expire at various years beginning with 2036
State credit carryforwards [Member]
Income Taxes [Line Items]
NOL carryforwards		$ 26,900,000
NOL carryforwards expiration		expire at various years beginning with 2036
State credit carryforwards [Member] | Research Tax Credit Carryforward [Member]
Income Taxes [Line Items]
Tax credit carryforwards		$ 4,600,000
Foreign Tax Authority [Member]
Income Taxes [Line Items]
NOL carryforwards		$ 70,100,000

Income Taxes - Schedule of Comp

Income Taxes - Schedule of Components of Loss Before Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
U.S.	$ (59,426)	$ (45,024)
Foreign	(5,060)	(28,853)
Net loss before income taxes	$ (64,486)	$ (73,877)

Income Taxes - Schedule of Reco

Income Taxes - Schedule of Reconciliation of Income Tax Expense Computed Statutory Federal Income Tax and Financial Statements (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Federal income tax expense at statutory rate		$ (13,542,000)	$ (15,514,000)
Stock compensation		(1,212,000)	(1,512,000)
Non-deductible expenses		307,000	75,000
Other		298,000	41,000
Research and development tax credits		(948,000)	(1,215,000)
Change in valuation allowance		18,312,000	11,219,000
Foreign rate differential		(212,000)	(586,000)
State deferred tax adjustment		3,239,000
Change in state uncertain tax positions		(6,242,000)	6,242,000
Total tax benefit	$ (1,300,000)	$ 0	$ (1,250,000)

Income Taxes - Schedule of Defe

Income Taxes - Schedule of Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Net operating loss carryforwards	$ 53,309	$ 37,247
Accruals, reserve and other	834	827
Stock-based compensation	4,767	4,549
Tax credit carryforwards	6,008	4,161
Property and equipment		310
Intangibles	24	38
Lease obligation	6,896
Other	151	122
Total deferred tax assets before valuation allowance	71,989	47,254
Valuation allowance	(66,201)	$ (47,254)
Total deferred tax assets	5,788
Deferred tax liabilities:
Property and equipment	(1,305)
Right-of-use assets	(4,483)
Total deferred tax liabilities	$ (5,788)

Income Taxes - Schedule of Unre

Income Taxes - Schedule of Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Unrecognized tax benefits as of the beginning of the year	$ 8,805	$ 2,745
Increase (decrease) related to prior year tax provisions	(6,242)	1,941
Increase related to current year tax provisions	995	4,119
Unrecognized tax benefits as of the end of the year	$ 3,558	$ 8,805

Net Loss per Share - Schedule o

Net Loss per Share - Schedule of Antidilutive Common Stock Equivalents Excluded from Calculation of Diluted Net Loss Per Share (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive common stock equivalents excluded from calculation of diluted net loss per share	10,221	8,996
Stock Options [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive common stock equivalents excluded from calculation of diluted net loss per share	8,995	6,447
Restricted Stock Units [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive common stock equivalents excluded from calculation of diluted net loss per share	1,121	2,397
ESPP [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive common stock equivalents excluded from calculation of diluted net loss per share	15	62
Warrants to Purchase Common Stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive common stock equivalents excluded from calculation of diluted net loss per share	90	90

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	May 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Related Party Transaction [Line Items]
Cash purchase price		$ 25,755	$ 70,187
Common Stock [Member]
Related Party Transaction [Line Items]
Issuance of common stock		2,436	11,642
Common Stock [Member] | Trust [Member]
Related Party Transaction [Line Items]
Issuance of common stock	20,000
Share price	$ 6.71
Cash purchase price	$ 100

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Feb. 29, 2020	Dec. 31, 2019	Dec. 31, 2018
Subsequent Event [Line Items]
Proceeds from issuance of common stock, after deducting underwriting discounts and commissions and estimated offering expenses		$ 25,755	$ 70,187
Subsequent Event [Member]
Subsequent Event [Line Items]
Issuance of common stock	10,925,000
Proceeds from issuance of common stock, after deducting underwriting discounts and commissions and estimated offering expenses	$ 140,800