Adverum Biotechnologies (ADVM) 10-Q 4 Nov 21 2021 Q3 Quarterly report Financial data

Cover Page

Cover Page - shares	9 Months Ended
	Sep. 30, 2021	Oct. 29, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2021
Document Transition Report	false
Entity File Number	001-36579
Entity Registrant Name	Adverum Biotechnologies, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	20-5258327
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
Title of 12(b) Security	Common Stock, $0.0001 par value
Trading Symbol	ADVM
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		98,152,090
Amendment Flag	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Entity Central Index Key	0001501756
Current Fiscal Year End Date	--12-31

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 32,971	$ 62,424
Short-term investments	299,734	367,305
Lease incentive receivables	7,358	0
Prepaid expenses and other current assets	7,764	4,709
Total current assets	347,827	434,438
Operating lease right-of-use assets	100,174	19,376
Property and equipment, net	37,158	27,725
Restricted cash	5,284	999
Deposit and other long-term assets	138	29
Total assets	490,581	482,567
Current liabilities:
Accounts payable	2,517	2,810
Accrued expenses and other current liabilities	18,585	13,588
Lease liability, current portion	4,224	4,473
Total current liabilities	25,326	20,871
Lease liability, net of current portion	118,141	26,235
Other non-current liabilities	1,114	1,114
Total liabilities	144,581	48,220
Stockholders’ equity:
Preferred stock	0	0
Common stock	10	10
Additional paid-in capital	960,180	937,134
Accumulated other comprehensive loss	(523)	(261)
Accumulated deficit	(613,667)	(502,536)
Total stockholders’ equity	346,000	434,347
Total liabilities and stockholders' equity	$ 490,581	$ 482,567

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Statement [Abstract]
License revenue	$ 0	$ 0	$ 7,500,000	$ 0
Operating expenses:
Research and development	24,069,000	16,653,000	66,657,000	50,581,000
General and administrative	14,453,000	11,351,000	52,546,000	30,989,000
Total operating expenses	38,522,000	28,004,000	119,203,000	81,570,000
Operating loss	(38,522,000)	(28,004,000)	(111,703,000)	(81,570,000)
Other income, net	160,000	235,000	572,000	1,695,000
Net loss	(38,362,000)	(27,769,000)	(111,131,000)	(79,875,000)
Other comprehensive income (loss):
Net unrealized (loss)/gain on marketable securities	(55,000)	(20,000)	(139,000)	120,000
Foreign currency translation adjustment	(51,000)	13,000	(123,000)	0
Comprehensive loss	$ (38,468,000)	$ (27,776,000)	$ (111,393,000)	$ (79,755,000)
Net loss per share — basic (in USD per share)	$ (0.39)	$ (0.31)	$ (1.13)	$ (0.99)
Net loss per share — diluted (in USD per share)	$ (0.39)	$ (0.31)	$ (1.13)	$ (0.99)
Weighted-average common shares used to compute net loss per share - basic (in shares)	98,126	88,867	97,966	80,995
Weighted-average common shares used to compute net loss per share - diluted (in shares)	98,126	88,867	97,966	80,995

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Stockholders Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive (Loss)/Income	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2019		67,329,000
Beginning balance at Dec. 31, 2019	$ 174,957	$ 7	$ 560,704	$ (725)	$ (385,029)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	3,409		3,409
Issuance of common stock, net of issuance costs (in shares)		10,925,000
Issuance of common stock, net of issuance costs	140,873	$ 1	140,872
Common stock issued upon exercise of stock options (in shares)		1,310,000
Common stock issued upon exercise of stock options	9,650		9,650
Common stock issued upon net exercise of warrants (in shares)		7,000
Common stock issued upon release of restricted stock units (in shares)		462,000
Restricted stock surrendered for taxes (in shares)		(155,000)
Restricted stock surrendered for taxes	(1,922)		(1,922)
Foreign currency translation adjustments	(54)			(54)
Unrealized gain (loss) on marketable securities, net	(54)			(54)
Net loss	(22,906)				(22,906)
Ending balance (in shares) at Mar. 31, 2020		79,878,000
Ending balance at Mar. 31, 2020	303,953	$ 8	712,713	(833)	(407,935)
Beginning balance (in shares) at Dec. 31, 2019		67,329,000
Beginning balance at Dec. 31, 2019	174,957	$ 7	560,704	(725)	(385,029)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Foreign currency translation adjustments	0
Unrealized gain (loss) on marketable securities, net	120
Net loss	(79,875)
Ending balance (in shares) at Sep. 30, 2020		97,467,000
Ending balance at Sep. 30, 2020	464,712	$ 10	930,211	(605)	(464,904)
Beginning balance (in shares) at Mar. 31, 2020		79,878,000
Beginning balance at Mar. 31, 2020	303,953	$ 8	712,713	(833)	(407,935)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	4,785		4,785
Common stock issued upon exercise of stock options (in shares)		643,000
Common stock issued upon exercise of stock options	2,487		2,487
Common stock issued upon release of restricted stock units (in shares)		66,000
Issuance of common stock, additional issuance costs	(51)		(51)
Common stock issued under employee stock purchase plan (in shares)		57,000
Common stock issued under employee stock purchase plan	475		475
Restricted stock surrendered for taxes (in shares)		(5,000)
Restricted stock surrendered for taxes	(121)		(121)
Taxes paid for RSUs	0		0
Foreign currency translation adjustments	41			41
Unrealized gain (loss) on marketable securities, net	194			194
Net loss	(29,200)				(29,200)
Ending balance (in shares) at Jun. 30, 2020		80,639,000
Ending balance at Jun. 30, 2020	282,563	$ 8	720,288	(598)	(437,135)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	6,020		6,020
Issuance of common stock, net of issuance costs (in shares)		16,675,000
Issuance of common stock, net of issuance costs	203,383	$ 2	203,381
Common stock issued upon exercise of stock options (in shares)		83,000
Common stock issued upon exercise of stock options	516		516
Common stock issued upon net exercise of warrants (in shares)		29,000
Common stock issued upon release of restricted stock units (in shares)		43,000
Common stock issued under employee stock purchase plan (in shares)		1,000
Common stock issued under employee stock purchase plan	6		6
Restricted stock surrendered for taxes (in shares)		(3,000)
Foreign currency translation adjustments	13			13
Unrealized gain (loss) on marketable securities, net	(20)			(20)
Net loss	(27,769)				(27,769)
Ending balance (in shares) at Sep. 30, 2020		97,467,000
Ending balance at Sep. 30, 2020	464,712	$ 10	930,211	(605)	(464,904)
Beginning balance (in shares) at Dec. 31, 2020		97,549,000
Beginning balance at Dec. 31, 2020	434,347	$ 10	937,134	(261)	(502,536)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	7,224		7,224
Issuance of common stock, net of issuance costs (in shares)		121,000
Issuance of common stock, net of issuance costs	1,689		1,689
Common stock issued upon exercise of stock options (in shares)		9,000
Common stock issued upon exercise of stock options	51		51
Common stock issued upon release of restricted stock units (in shares)		248,000
Restricted stock surrendered for taxes (in shares)		0
Restricted stock surrendered for taxes	0
Foreign currency translation adjustments	(33)			(33)
Unrealized gain (loss) on marketable securities, net	(22)			(22)
Net loss	(28,436)				(28,436)
Ending balance (in shares) at Mar. 31, 2021		97,927,000
Ending balance at Mar. 31, 2021	414,820	$ 10	946,098	(316)	(530,972)
Beginning balance (in shares) at Dec. 31, 2020		97,549,000
Beginning balance at Dec. 31, 2020	$ 434,347	$ 10	937,134	(261)	(502,536)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issued upon exercise of stock options (in shares)	9,000
Foreign currency translation adjustments	$ (123)
Unrealized gain (loss) on marketable securities, net	(139)
Net loss	(111,131)
Ending balance (in shares) at Sep. 30, 2021		98,143,000
Ending balance at Sep. 30, 2021	346,000	$ 10	960,180	(523)	(613,667)
Beginning balance (in shares) at Mar. 31, 2021		97,927,000
Beginning balance at Mar. 31, 2021	414,820	$ 10	946,098	(316)	(530,972)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	8,234		8,234
Common stock issued upon release of restricted stock units (in shares)		17,000
Issuance of common stock, additional issuance costs	(4)		(4)
Common stock issued under employee stock purchase plan (in shares)		176,000
Common stock issued under employee stock purchase plan	526		526
Foreign currency translation adjustments	(39)			(39)
Unrealized gain (loss) on marketable securities, net	(62)			(62)
Net loss	(44,333)				(44,333)
Ending balance (in shares) at Jun. 30, 2021		98,120,000
Ending balance at Jun. 30, 2021	379,142	$ 10	954,854	(417)	(575,305)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	5,326		5,326
Common stock issued upon release of restricted stock units (in shares)		23,000
Foreign currency translation adjustments	(51)			(51)
Unrealized gain (loss) on marketable securities, net	(55)			(55)
Net loss	(38,362)				(38,362)
Ending balance (in shares) at Sep. 30, 2021		98,143,000
Ending balance at Sep. 30, 2021	$ 346,000	$ 10	$ 960,180	$ (523)	$ (613,667)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Stockholders Equity (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Sep. 30, 2020	Mar. 31, 2020
Statement of Stockholders' Equity [Abstract]
Stock issuance costs	$ 5	$ 385	$ 332

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash flows from operating activities:
Net loss	$ (111,131)	$ (79,875)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	3,323	3,081
Stock-based compensation expense	20,784	14,214
Amortization of premium/(discount) and accrued interest on marketable securities	2,273	(773)
Impairment of long-lived assets	1,072	0
Other	(132)	25
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(3,493)	5,194
Other assets	(109)	(8)
Operating lease right-of-use asset	2,825	1,265
Accounts payable	(587)	1,444
Accrued expenses and other current liabilities	3,253	(573)
Lease liability and lease incentive receivable	(94)	(1,061)
Net cash used in operating activities	(82,016)	(57,067)
Cash flows from investing activities:
Purchases of marketable securities	(328,275)	(511,845)
Maturities of marketable securities	384,882	223,765
Sales of marketable securities	8,990	6,748
Purchases of property and equipment	(10,771)	(10,411)
Net cash provided by (used in) investing activities	54,826	(291,743)
Cash flows from financing activities:
Proceeds from offerings of common stock, net of issuance costs	1,685	344,547
Proceeds from issuance of common stock pursuant to option exercises	51	12,653
Taxes paid related to net share settlement of restricted stock units	0	(2,043)
Proceeds from employee stock purchase plan	526	481
Repayment of loan	(240)	(29)
Net cash provided by financing activities	2,022	355,609
Net (decrease) increase in cash and cash equivalents and restricted cash	(25,168)	6,799
Cash and cash equivalents and restricted cash at beginning of period	63,423	66,896
Cash and cash equivalents and restricted cash at end of period	38,255	73,695
Cash and cash equivalents	32,971	72,696
Restricted cash	5,284	999
Cash and cash equivalents and restricted cash at end of period	38,255	73,695
Supplemental schedule of noncash investing and financing information
Right-of-use assets obtained in exchange for lease liability	84,005	0
Fixed assets in accounts payable, accrued expenses and other current liabilities	$ 2,675	$ 325

Organization and Basis of Prese

Organization and Basis of Presentation	9 Months Ended
	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Basis of Presentation	Organization and Basis of Presentation 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 intended to provide durable efficacy by inducing sustained expression of a therapeutic protein. The Company’s core capabilities include novel vector discovery, preclinical and clinical development, and pre-commercial planning. In addition, the Company has in-house manufacturing expertise, specifically in scalable process development, assay development, and current Good Manufacturing Practices (“GMP”) quality control. 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 $613.7 million as of September 30, 2021. The Company expects to incur losses and have negative net cash flows from operating activities as it engages in further research and development activities. As of September 30, 2021, the Company had cash, cash equivalents and short-term investments of $332.7 million, which the Company believes will be sufficient to fund its operations for at least twelve months from the date of issuance of these financial statements. Basis of Presentation — The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) and follow the requirements of the Securities and Exchange Commission (“SEC”) for interim reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by U.S. GAAP can be condensed or omitted. These unaudited condensed consolidated financial statements have been prepared on the same basis as the Company’s annual consolidated financial statements and, in the opinion of management, reflect all adjustments, consisting only of normal recurring adjustments, which are necessary for a fair statement of the Company’s consolidated financial information. The results of operations for the three and nine months ended September 30, 2021 are not necessarily indicative of the results to be expected for the full year or any other future period. The balance sheet as of December 31, 2020 is derived from the audited consolidated financial statements at that date but does not include all of the information required by U.S. GAAP for complete consolidated financial statements. The Company's results of operations and financial condition for the nine months ended September 30, 2021 were not significantly impacted by the novel coronavirus disease ("COVID-19") pandemic. The accompanying unaudited condensed consolidated financial statements and related financial information should be read in conjunction with the audited consolidated financial statements and the related notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020 filed with the SEC.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Use of Estimates The accompanying condensed consolidated financial statements have been prepared in accordance with U.S. GAAP. The preparation of the condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent liabilities and the reported amounts of expenses in the condensed consolidated financial statements and the accompanying notes. On an ongoing basis, management evaluates its estimates, including those related to clinical trial accruals, fair value of assets and liabilities, impairment of long-lived assets, income taxes, and stock-based compensation. Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable under the circumstances. Actual results could differ from those estimates. Recent Accounting Pronouncements In June 2016, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2016-13, Financial Instruments – Credit Losses: Measurement of Credit Losses on Financial Instruments (“ Topic 326 ”) and also issued subsequent amendments to the initial guidance: ASU 2018-19, ASU 2019-04, ASU 2019-05, and ASU 2019-11. The standard requires that financial assets measured at amortized cost be presented at the net amount expected to be collected. The measurement of expected credit losses is based on historical experience, current conditions, and reasonable and supportable forecasts that affect collectability. Topic 326 also eliminates the concept of “other-than-temporary” impairment when evaluating available-for-sale debt securities and instead focuses on determining whether any impairment is a result of a credit loss or other factors. An entity will recognize an allowance for credit losses on available-for-sale debt securities rather than an other-than-temporary impairment that reduces the cost basis of the investment. Topic 326 will become effective for the Company on January 1, 2023. Early adoption is permitted. The Company is currently evaluating the impact of adopting Topic 326, but does not expect the effect of adoption to be material. In December 2019, the FASB issued Accounting Standards Update No. 2019-12, Income Taxes (" Topic 740" ): Simplifying the Accounting for Income Taxes ("ASU 2019-12"). The ASU simplifies the accounting for income taxes by removing certain exceptions to the general principles in Topic 740. The ASU also improves consistent application of and simplify GAAP for other areas of Topic 740 by clarifying and amending existing guidance. This standard is effective for fiscal years beginning after December 15, 2020. The Company adopted this standard as of January 1, 2021 on a prospective basis in accordance with ASC 250, Accounting Changes and Error Corrections. Adoption of the new guidance had no significant impact on the Company's consolidated financial statements.

Fair Value Measurements and Fai

Fair Value Measurements and Fair Value of Financial Instruments	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements and Fair Value of Financial Instruments	Fair Value Measurements and Fair Value of Financial Instruments The authoritative guidance on the fair value hierarchy for disclosure of fair value measurements is 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. 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, and corporate bond are valued primarily using market prices of comparable securities, bid/ask quotes, interest rate yields and prepayment spreads and are included in Level 2. The following is a summary of the Company’s cash equivalents and short-term investments: September 30, 2021 Amortized Cost Basis Unrealized Gains Unrealized Estimated Fair Value (In thousands) Level 1: Money market funds $ 27,019 $ — $ — $ 27,019 Level 2: U.S. government and agency securities 90,665 8 (25) 90,648 Commercial paper 157,111 10 (5) 157,116 Corporate bonds 51,986 — (16) 51,970 Total cash equivalents and short-term investments 326,781 18 (46) 326,753 Less: cash equivalents (27,019) — — (27,019) Total short-term investments $ 299,762 $ 18 $ (46) $ 299,734 December 31, 2020 Amortized Cost Basis Unrealized Gains Unrealized Estimated Fair Value (In thousands) Level 1: Money market funds $ 178 $ — $ — $ 178 Level 2: U.S. government and agency securities 328,583 121 (5) 328,699 Commercial paper 97,324 — (5) 97,319 Total cash equivalents and short-term investments 426,085 121 (10) 426,196 Less: cash equivalents (58,894) — 3 (58,891) Total short-term investments $ 367,191 $ 121 $ (7) $ 367,305 As of September 30, 2021, $57.4 million of marketable securities had remaining maturities between one

Revenue

Revenue	9 Months Ended
	Sep. 30, 2021
Revenue from Contract with Customer [Abstract]
Revenue	Revenue On January 25, 2021, the Company and Lexeo Therapeutics, Inc (“Lexeo”) entered into a License Agreement pursuant to which the Company granted Lexeo an exclusive, worldwide, royalty-bearing license to certain of the Company's intellectual property to develop, manufacture, and commercialize a gene therapy product to treat cardiomyopathy due to Friedreich's ataxia. Upon execution of the agreement, Lexeo paid the Company a one-time, non-creditable and non-refundable upfront payment of $7.5 million. Under the terms of the agreement, the Company is eligible to receive development and commercial milestone payments and royalties on sales of Lexeo's licensed products once commercialized. Under Topic 606, the initial transaction price is the $7.5 million the Company received for the license granted. The arrangement provides for additional payments to the Company when certain development and commercial milestones are achieved. Because these milestone payments are not within the control of the Company and are not considered probable of being achieved until the events occur, the Company did not include them in the transaction price. The transaction price of $7.5 million was allocated to a combined performance obligation that was fulfilled during the three months ended March 31, 2021. The Company recognized no revenue in the three months ended September 30, 2021 and $7.5 million of license revenue during nine months ended September 30, 2021.

Leases

Leases	9 Months Ended
	Sep. 30, 2021
Leases [Abstract]
Leases	Leases Redwood City, CA Existing Lease The Company leases its office and laboratory space pursuant to an operating lease ("Existing Lease"), which commenced on September 1, 2018 and had an original lease term expiring in February 2029. Upon the execution of the Existing Lease, the Company provided the landlord with a letter of credit in the amount of $1.0 million, which was returned after receipt of the replacement letter of credit in conjunction with the execution of the expansion lease below. On November 1, 2021, the Company entered into an amendment to terminate the lease of one of its premises under the Existing Lease and paid a termination fee of $0.4 million. As of September 30, 2021 , the Company has an operating right-of-use asset of $15.9 million and an operating lease obligation of $21.5 million relating to this lease, which represents $30.8 million of undiscounted lease payments less $9.3 million of present value adjustment. Concurrently, the Company entered into an agreement to sublease a portion of such premises at $0.1 million monthly base rent. The sublease will expire on March 31, 2022 and may be extended on a month to month basis until June 30, 2022. As of September 30, 2021, the Company evaluated its plans for the leased facilities including the decision to terminate and vacate certain leased office space under the Existing Lease. This change in the circumstances resulted in the requirement to test the recoverability of the carrying amount of the asset group. As of September 30, 2021, the carrying amount of the asset group, consisting of right-of-use assets and leasehold improvements, relating to one of the premises under Existing Lease to be terminated exceeds the Company's anticipated undiscounted cash flows. Accordingly, the Company reviewed the related right-of-use assets and leasehold improvements for impairment. As a result of the evaluation, the Company recorded an impairment charge of $1.1 million, which includes $0.8 million associated with the right-of-use assets and $0.3 million associated with leasehold improvements, for the three and nine months ended September 30, 2021. The assets indicated as impaired were written down to the estimated fair value, which was determined using the terms of the termination and sublease agreements. Redwood City, CA Expansion Lease On April 22, 2021, the Company entered into the first amendment to the Existing Lease pursuant to which the Company leased an additional building (the “Expansion Premises”) with a term of ten years ("Expansion Lease"). The Expansion Lease commenced on June 9, 2021 and has a lease term expiring in December 2031. The Expansion Lease provides a total of tenant improvement allowances of up to $10.2 million. On the execution of the Expansion Lease, the Company provided the landlord with a letter of credit in the amount of $2.5 million, which is classified as restricted cash under long term assets on the Company's condensed consolidated balance sheets, and replaced the letter of credit delivered in connection with the Existing Lease. The first amendment to the Existing Lease also extends the term of the Existing Lease to expire in December 2031, with an option to extend the Existing Lease and the Expansion Lease for a period of eight years. North Carolina Lease On January 8, 2021, the Company entered into an operating lease agreement for a building in North Carolina ("NC Premises"). The lease commenced in April 2021 when the Company obtained control of the NC Premises, and the lease term expires in October 2037 with two options to extend the lease term for a period of five years each. The Company had the right to make tenant improvements with a lease incentive allowance of up to $25.5 million. The Company made the rent payment for the first month upon commencement of the lease. Thereafter, the rent payments begin in November 2022. The North Carolina Lease provides for an escalation of rent payment each year. In connection with the lease, the Company provided the landlord with a letter of credit in the amount of $2.8 million, which is classified as restricted cash under long term assets on the condensed consolidated balance sheet as of September 30, 2021. The $2.8 million was replaced by a security deposit pledged by the subtenant to the Company as part of the sublease agreement entered on October 26, 2021 below. As of September 30, 2021, the Company evaluated its plans for the leased facilities including the decision to sublease the North Carolina facility. This change in the circumstances resulted in the requirement to test the recoverability of the carrying amount of the asset group. The impairment test was performed at the right-of-use asset and the leasehold improvements level, representing the lowest identifiable levels of cash flows. On October 26, 2021, the Company entered into a sublease agreement with a subtenant for the NC Premises. The sublease commences on October 26, 2021 and expires on October 31, 2037. The base annual rental rates, payment schedules and amounts under the sublease agreement are substantially the same as the original payment terms by Adverum to the landlord. Sublease income is approximately $108.2 million over the term of the lease excluding share of facilities operating expenses. As of September 30, 2021, the undiscounted value of the sublease income over the sublease term exceeds the carrying amount of the asset group relating to the NC Premises. The Company determined that there was no impairment related to the NC Premises. As of September 30, 2021, the weighted-average remaining lease term was 12.1 years for the Company's leases and the weighted-average Incremental Borrowing Rate (“IBR”) was 6.79%. IBR is an estimated rate of interest used to determine present value of future lease payments in order to measure lease liability, which rate is what the Company would pay to borrow equivalent funds on a collateralized basis at the lease commencement date. In order to determine the IBR, the Company estimates its credit rating, adjusts the credit rating for the nature of the collateral, and benchmarks the borrowing rate against observable yields on comparable securities with a similar term. As of September 30, 2021, the undiscounted future non-cancellable lease payments under the lease agreements, after giving effect to the amendment to terminate one of its premises under the Existing lease and the sublease of the NC Premises, are as follows (in thousands): Year ending December 31, Operating Leases Sublease Payments Receivable 2021 (remaining 3 months) $ 818 $ 463 2022 6,049 491 2023 13,947 5,844 2024 14,405 6,019 2025 14,880 6,200 Thereafter 149,252 89,136 Total undiscounted lease payments 199,351 $ 108,153 Less: Present value adjustment (75,629) Less: Tenant improvement allowance (30,015) Add: Lease incentive receivable 7,358 Total lease liability as of September 30, 2021 $ 101,065 Rent expense for the three months ended September 30, 2021 and 2020 was $4.3 million, and $1.3 million, respectively, including variable lease cost of $0.6 million and $0.4 million, respectively. Variable lease costs includes utilities, parking, maintenance, and real estate taxes. Rent expense for the nine months ended September 30, 2021 and 2020 was $8.5 million, and $4.4 million, respectively, including variable lease cost of $1.3 million and $1.1 million, respectively.

Balance Sheet Components

Balance Sheet Components	9 Months Ended
	Sep. 30, 2021
Balance Sheet Related Disclosures [Abstract]
Balance Sheet Components	Balance Sheet Components Property and Equipment, Net Property and equipment, net consists of the following: September 30, 2021 December 31, 2020 (In thousands) Computer equipment and software $ 1,212 $ 599 Laboratory equipment 11,065 9,354 Furniture and fixtures 1,484 1,259 Leasehold improvements 28,393 24,631 Construction in progress 8,329 1,954 Total property and equipment 50,483 37,797 Less accumulated depreciation and amortization (13,325) (10,072) Property and equipment, net $ 37,158 $ 27,725 Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consist of the following: September 30, 2021 December 31, 2020 (In thousands) Employee compensation $ 8,557 $ 8,344 Accrued preclinical, clinical and process development costs 5,904 2,844 State income tax payable 1,249 40 Accrued professional services 549 1,075 Other 2,326 1,285 Total accrued expenses and other current liabilities $ 18,585 $ 13,588

Equity Incentive Awards

Equity Incentive Awards	9 Months Ended
	Sep. 30, 2021
Share-based Payment Arrangement [Abstract]
Equity Incentive Awards	Equity Incentive Awards Stock Options The following table summarizes the Company’s option activity and related information: Number of Weighted- Balance at December 31, 2020 10,432 $ 11.65 Options granted 6,863 8.02 Options exercised (9) 5.86 Options forfeited (3,427) 11.43 Balance at September 30, 2021 13,859 $ 9.91 Exercisable as of September 30, 2021 5,724 $ 10.11 Restricted Stock Units (“RSUs”) The following table summarizes the Company’s RSUs activity and related information: Number of Units Weighted- Outstanding at December 31, 2020 540 $ 6.41 Granted 2,570 3.91 Vested and released (289) 5.35 Forfeited (228) 8.95 Outstanding at September 30, 2021 2,593 $ 3.83 RSUs granted during the three months ended September 30, 2021 include 1.3 million shares of performance units with both performance and service vesting conditions. Stock-Based Compensation Expense The following table presents, by operating expense, the Company’s stock-based compensation expense: Three Months Ended Nine Months Ended 2021 2020 2021 2020 (In thousands) Research and development $ 2,207 $ 2,051 $ 7,125 $ 4,967 General and administrative 3,119 3,969 13,659 9,247 Total stock-based compensation expense $ 5,326 $ 6,020 $ 20,784 $ 14,214 During the nine months ended September 30, 2021, the Company recorded stock-based compensation expenses of approximately $1.6 million, as a result of modifications to certain directors' and officers' stock awards during the periods.

Net Loss per Share

Net Loss per Share	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Net Loss per Share	Net Loss per ShareBasic 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, RSUs, rights under the 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. 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: September 30, 2021 September 30, 2020 (In thousands) Stock options 13,859 10,262 Restricted stock units 2,593 558 ESPP 400 66 Warrants to purchase common stock — 40 16,852 10,926

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation — The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) and follow the requirements of the Securities and Exchange Commission (“SEC”) for interim reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by U.S. GAAP can be condensed or omitted. These unaudited condensed consolidated financial statements have been prepared on the same basis as the Company’s annual consolidated financial statements and, in the opinion of management, reflect all adjustments, consisting only of normal recurring adjustments, which are necessary for a fair statement of the Company’s consolidated financial information. The results of operations for the three and nine months ended September 30, 2021 are not necessarily indicative of the results to be expected for the full year or any other future period. The balance sheet as of December 31, 2020 is derived from the audited consolidated financial statements at that date but does not include all of the information required by U.S. GAAP for complete consolidated financial statements. The Company's results of operations and financial condition for the nine months ended September 30, 2021 were not significantly impacted by the novel coronavirus disease ("COVID-19") pandemic.
Use of Estimates	Use of Estimates The accompanying condensed consolidated financial statements have been prepared in accordance with U.S. GAAP. The preparation of the condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent liabilities and the reported amounts of expenses in the condensed consolidated financial statements and the accompanying notes. On an ongoing basis, management evaluates its estimates, including those related to clinical trial accruals, fair value of assets and liabilities, impairment of long-lived assets, income taxes, and stock-based compensation. Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable under the circumstances. Actual results could differ from those estimates.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In June 2016, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2016-13, Financial Instruments – Credit Losses: Measurement of Credit Losses on Financial Instruments (“ Topic 326 ”) and also issued subsequent amendments to the initial guidance: ASU 2018-19, ASU 2019-04, ASU 2019-05, and ASU 2019-11. The standard requires that financial assets measured at amortized cost be presented at the net amount expected to be collected. The measurement of expected credit losses is based on historical experience, current conditions, and reasonable and supportable forecasts that affect collectability. Topic 326 also eliminates the concept of “other-than-temporary” impairment when evaluating available-for-sale debt securities and instead focuses on determining whether any impairment is a result of a credit loss or other factors. An entity will recognize an allowance for credit losses on available-for-sale debt securities rather than an other-than-temporary impairment that reduces the cost basis of the investment. Topic 326 will become effective for the Company on January 1, 2023. Early adoption is permitted. The Company is currently evaluating the impact of adopting Topic 326, but does not expect the effect of adoption to be material. In December 2019, the FASB issued Accounting Standards Update No. 2019-12, Income Taxes (" Topic 740" ): Simplifying the Accounting for Income Taxes ("ASU 2019-12"). The ASU simplifies the accounting for income taxes by removing certain exceptions to the general principles in Topic 740. The ASU also improves consistent application of and simplify GAAP for other areas of Topic 740 by clarifying and amending existing guidance. This standard is effective for fiscal years beginning after December 15, 2020. The Company adopted this standard as of January 1, 2021 on a prospective basis in accordance with ASC 250, Accounting Changes and Error Corrections. Adoption of the new guidance had no significant impact on the Company's consolidated financial statements.

Fair Value Measurements and F_2

Fair Value Measurements and Fair Value of Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2021
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: September 30, 2021 Amortized Cost Basis Unrealized Gains Unrealized Estimated Fair Value (In thousands) Level 1: Money market funds $ 27,019 $ — $ — $ 27,019 Level 2: U.S. government and agency securities 90,665 8 (25) 90,648 Commercial paper 157,111 10 (5) 157,116 Corporate bonds 51,986 — (16) 51,970 Total cash equivalents and short-term investments 326,781 18 (46) 326,753 Less: cash equivalents (27,019) — — (27,019) Total short-term investments $ 299,762 $ 18 $ (46) $ 299,734 December 31, 2020 Amortized Cost Basis Unrealized Gains Unrealized Estimated Fair Value (In thousands) Level 1: Money market funds $ 178 $ — $ — $ 178 Level 2: U.S. government and agency securities 328,583 121 (5) 328,699 Commercial paper 97,324 — (5) 97,319 Total cash equivalents and short-term investments 426,085 121 (10) 426,196 Less: cash equivalents (58,894) — 3 (58,891) Total short-term investments $ 367,191 $ 121 $ (7) $ 367,305

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2021
Leases [Abstract]
Schedule of Undiscounted Future Lease Payments under Operating Lease	As of September 30, 2021, the undiscounted future non-cancellable lease payments under the lease agreements, after giving effect to the amendment to terminate one of its premises under the Existing lease and the sublease of the NC Premises, are as follows (in thousands): Year ending December 31, Operating Leases Sublease Payments Receivable 2021 (remaining 3 months) $ 818 $ 463 2022 6,049 491 2023 13,947 5,844 2024 14,405 6,019 2025 14,880 6,200 Thereafter 149,252 89,136 Total undiscounted lease payments 199,351 $ 108,153 Less: Present value adjustment (75,629) Less: Tenant improvement allowance (30,015) Add: Lease incentive receivable 7,358 Total lease liability as of September 30, 2021 $ 101,065

Balance Sheet Components (Table

Balance Sheet Components (Tables)	9 Months Ended
	Sep. 30, 2021
Balance Sheet Related Disclosures [Abstract]
Schedule of Property and Equipment, Net	Property and equipment, net consists of the following: September 30, 2021 December 31, 2020 (In thousands) Computer equipment and software $ 1,212 $ 599 Laboratory equipment 11,065 9,354 Furniture and fixtures 1,484 1,259 Leasehold improvements 28,393 24,631 Construction in progress 8,329 1,954 Total property and equipment 50,483 37,797 Less accumulated depreciation and amortization (13,325) (10,072) Property and equipment, net $ 37,158 $ 27,725
Schedule of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consist of the following: September 30, 2021 December 31, 2020 (In thousands) Employee compensation $ 8,557 $ 8,344 Accrued preclinical, clinical and process development costs 5,904 2,844 State income tax payable 1,249 40 Accrued professional services 549 1,075 Other 2,326 1,285 Total accrued expenses and other current liabilities $ 18,585 $ 13,588

Equity Incentive Awards (Tables

Equity Incentive Awards (Tables)	9 Months Ended
	Sep. 30, 2021
Share-based Payment Arrangement [Abstract]
Summary of Stock Options Activity	The following table summarizes the Company’s option activity and related information: Number of Weighted- Balance at December 31, 2020 10,432 $ 11.65 Options granted 6,863 8.02 Options exercised (9) 5.86 Options forfeited (3,427) 11.43 Balance at September 30, 2021 13,859 $ 9.91 Exercisable as of September 30, 2021 5,724 $ 10.11
Summary of Restricted Stock Units Activity	The following table summarizes the Company’s RSUs activity and related information: Number of Units Weighted- Outstanding at December 31, 2020 540 $ 6.41 Granted 2,570 3.91 Vested and released (289) 5.35 Forfeited (228) 8.95 Outstanding at September 30, 2021 2,593 $ 3.83
Stock-Based Compensation Expense	The following table presents, by operating expense, the Company’s stock-based compensation expense: Three Months Ended Nine Months Ended 2021 2020 2021 2020 (In thousands) Research and development $ 2,207 $ 2,051 $ 7,125 $ 4,967 General and administrative 3,119 3,969 13,659 9,247 Total stock-based compensation expense $ 5,326 $ 6,020 $ 20,784 $ 14,214

Net Loss per Share (Tables)

Net Loss per Share (Tables)	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Schedule of Antidilutive Securities Excluded from Computation of Earnings 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: September 30, 2021 September 30, 2020 (In thousands) Stock options 13,859 10,262 Restricted stock units 2,593 558 ESPP 400 66 Warrants to purchase common stock — 40 16,852 10,926

Organization and Basis of Pre_2

Organization and Basis of Presentation (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accumulated deficit	$ 613,667	$ 613,667		$ 502,536
Cash, cash equivalents, and short-term investments	332,700	332,700
Impairment of long-lived assets	$ 1,100	$ 1,072	$ 0

Fair Value Measurements and F_3

Fair Value Measurements and Fair Value of Financial Instruments - Summary of Cash Equivalents and Short-term Investments (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	$ 299,762	$ 367,191
Unrealized Gains	18	121
Unrealized Losses	(46)	(7)
Estimated Fair Value	299,734	367,305
Less: Cash Equivalents, Amortized Cost Basis	(27,019)	(58,894)
Less: cash equivalents	0	0
Less: Cash equivalents, unrealized losses	0	3
Less: Cash equivalents, estimated fair value	(27,019)	(58,891)
Corporate bonds | Level 2
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	51,986
Unrealized Gains	0
Unrealized Losses	(16)
Estimated Fair Value	51,970
Total cash equivalents and short-term investments
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	326,781	426,085
Unrealized Gains	18	121
Unrealized Losses	(46)	(10)
Estimated Fair Value	326,753	426,196
Money market funds | Level 1
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	27,019	178
Unrealized Gains	0	0
Unrealized Losses	0	0
Estimated Fair Value	27,019	178
U.S. government and agency securities | Level 2
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	90,665	328,583
Unrealized Gains	8	121
Unrealized Losses	(25)	(5)
Estimated Fair Value	90,648	328,699
Commercial paper | Level 2
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	157,111	97,324
Unrealized Gains	10	0
Unrealized Losses	(5)	(5)
Estimated Fair Value	$ 157,116	$ 97,319

Fair Value Measurements and F_4

Fair Value Measurements and Fair Value of Financial Instruments - Additional Information (Detail) $ in Millions	Sep. 30, 2021USD ($)
Debt Securities, Available-for-sale [Line Items]
Marketable securities	$ 57.4
Minimum
Debt Securities, Available-for-sale [Line Items]
Marketable securities term	1 year
Maximum
Debt Securities, Available-for-sale [Line Items]
Marketable securities term	2 years

Revenue (Detail)

Revenue (Detail) - USD ($)	Jan. 25, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Revenue from Contract with Customer [Abstract]
License revenue	$ 7,500,000	$ 0	$ 0	$ 7,500,000	$ 0

Leases - Additional Information

Leases - Additional Information (Detail) $ in Thousands	Nov. 01, 2021USD ($)	Oct. 26, 2021USD ($)	Jan. 08, 2021USD ($)leaseExtensionOption	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Oct. 29, 2021USD ($)	Apr. 22, 2021USD ($)	Dec. 31, 2020USD ($)
Lessee, Lease, Description [Line Items]
Restricted cash				$ 5,284	$ 999	$ 5,284	$ 999			$ 999
Lease liability				101,065		101,065
Total undiscounted lease payments				199,351		199,351
Present value adjustment				75,629		75,629
Operating lease right-of-use assets				100,174		100,174				$ 19,376
Impairment of long-lived assets				1,100		1,072	0
Right-of-use asset, impairment loss				800		800
Leasehold improvements, impairment loss				300		300
Rent expense				4,300	1,300	8,500	4,400
Variable lease costs				600	$ 400	1,300	$ 1,100
Subsequent Event
Lessee, Lease, Description [Line Items]
Sublease income, full term of lease		$ 108,200
Terminated Lease
Lessee, Lease, Description [Line Items]
Lease liability				21,500		21,500
Total undiscounted lease payments				30,800		30,800
Present value adjustment				9,300		9,300
Operating lease right-of-use assets				15,900		15,900
Terminated Lease | Subsequent Event
Lessee, Lease, Description [Line Items]
Lease termination fees	$ 400
Sublease agreement, monthly cost								$ 100
Office Building And Laboratory
Lessee, Lease, Description [Line Items]
Restricted cash				1,000		1,000
Building
Lessee, Lease, Description [Line Items]
Restricted cash									$ 2,500
Lease term									10 years
Leasehold improvement allowance									$ 10,200
Lease renewal term									8 years
Manufacturing Facility
Lessee, Lease, Description [Line Items]
Restricted cash				$ 2,800		$ 2,800
Lease renewal term			5 years
Number of renewal contracts | leaseExtensionOption			2
Tenant improvement allowance			$ 25,500
Weighted-average remaining lease term				12 years 1 month 6 days		12 years 1 month 6 days
Weighted-average IBR				6.79%		6.79%
Manufacturing Facility | Subsequent Event
Lessee, Lease, Description [Line Items]
Cash released from restriction		$ 2,800

Leases - Schedule of Undiscount

Leases - Schedule of Undiscounted Future Lease Payments under Operating Lease (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Operating Leases
2021 (remaining 3 months)	$ 818
2022	6,049
2023	13,947
2024	14,405
2025	14,880
Thereafter	149,252
Total undiscounted lease payments	199,351
Less: Present value adjustment	(75,629)
Less: Tenant improvement allowance	(30,015)
Add: Lease incentive receivable	7,358	$ 0
Lease, liability	101,065
Sublease Payments Receivable
2021 (remaining 3 months)	463
2022	491
2023	5,844
2024	6,019
2025	6,200
Thereafter	89,136
Total undiscounted lease payments	$ 108,153

Balance Sheet Components - Sche

Balance Sheet Components - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 50,483	$ 37,797
Less accumulated depreciation and amortization	(13,325)	(10,072)
Property and equipment, net	37,158	27,725
Computer equipment and software
Property, Plant and Equipment [Line Items]
Total property and equipment	1,212	599
Laboratory equipment
Property, Plant and Equipment [Line Items]
Total property and equipment	11,065	9,354
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Total property and equipment	1,484	1,259
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property and equipment	28,393	24,631
Construction in progress
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 8,329	$ 1,954

Balance Sheet Components - Sc_2

Balance Sheet Components - Schedule of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Balance Sheet Related Disclosures [Abstract]
Employee compensation	$ 8,557	$ 8,344
Accrued preclinical, clinical and process development costs	5,904	2,844
State income tax payable	1,249	40
Accrued professional services	549	1,075
Other	2,326	1,285
Total accrued expenses and other current liabilities	$ 18,585	$ 13,588

Equity Incentive Awards - Summa

Equity Incentive Awards - Summary of Stock Options Activity (Detail) shares in Thousands	9 Months Ended
	Sep. 30, 2021$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Options Outstanding [Roll Forward]
Beginning balance (in shares) | shares	10,432
Options granted (in shares) | shares	6,863
Options exercised (in shares) | shares	(9)
Options forfeited (in shares) | shares	(3,427)
Ending balance (in shares) | shares	13,859
Exercisable (in shares) | shares	5,724
Weighted- Average Grant- Date Fair Value
Beginning balance (in USD per share) | $ / shares	$ 11.65
Options granted (in USD per share) | $ / shares	8.02
Options exercised (in USD per share) | $ / shares	5.86
Options forfeited (in USD per share) | $ / shares	11.43
Ending balance (in USD per share) | $ / shares	9.91
Exercisable (in USD per share) | $ / shares	$ 10.11

Equity Incentive Awards - Sum_2

Equity Incentive Awards - Summary of Restricted Stock Units Activity (Detail) - Restricted stock units shares in Thousands	9 Months Ended
	Sep. 30, 2021$ / sharesshares
Number of Units (in thousands)
Beginning balance (in shares) | shares	540
Granted (in shares) | shares	2,570
Vested and released (in shares) | shares	(289)
Forfeited (in shares) | shares	(228)
Ending balance (in shares) | shares	2,593
Weighted- Average Grant- Date Fair Value
Beginning balance (in USD per share) | $ / shares	$ 6.41
Granted (in USD per share) | $ / shares	3.91
Vested and released (in USD per share) | $ / shares	5.35
Forfeited (in USD per share) | $ / shares	8.95
Ending balance (in USD per share) | $ / shares	$ 3.83

Equity Incentive Awards - Addit

Equity Incentive Awards - Additional Information (Detail) - USD ($) shares in Millions, $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense as a result of modification		$ 1.6
Performance Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
RSUs granted (in shares)	1.3

Equity Incentive Awards - Stock

Equity Incentive Awards - Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	$ 5,326	$ 6,020	$ 20,784	$ 14,214
Research and development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	2,207	2,051	7,125	4,967
General and administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	$ 3,119	$ 3,969	$ 13,659	$ 9,247

Net Loss per Share - Schedule o

Net Loss per Share - Schedule of Common Stock Equivalents Outstanding (Detail) - shares shares in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from net loss per share (in shares)	16,852	10,926
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from net loss per share (in shares)	13,859	10,262
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from net loss per share (in shares)	2,593	558
ESPP
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from net loss per share (in shares)	400	66
Warrants to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from net loss per share (in shares)	0	40