Adverum Biotechnologies (ADVM) 10-Q 8 Nov 18 2018 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Oct. 31, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q3
Trading Symbol	ADVM
Entity Registrant Name	Adverum Biotechnologies, Inc.
Entity Central Index Key	1,501,756
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Common Stock, Shares Outstanding		62,868,379

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 159,673	$ 70,519
Short-term investments	58,209	119,966
Prepaid expenses and other current assets	4,292	3,256
Total current assets	222,174	193,741
Property and equipment, net	2,594	3,024
Restricted cash	999
Deposit and other long-term assets	140	140
Intangible asset		5,000
Total assets	225,907	201,905
Current liabilities:
Accounts payable	1,736	1,731
Accrued expenses and other current liabilities	7,777	6,964
Deferred rent, current portion	482	129
Deferred revenue, current portion	70	1,850
Total current liabilities	10,065	10,674
Deferred rent, net of current portion	102	222
Deferred revenue, net of current portion		5,250
Deferred tax liability		1,250
Other noncurrent liabilities	187	481
Total liabilities	10,354	17,877
Commitments and contingencies (Note 6)
Stockholders’ equity:
Preferred stock, $0.0001 par value, 5,000,000 shares authorized; no shares issued and outstanding
Common stock, $0.0001 par value, 300,000,000 shares authorized at September 30, 2018 and December 31, 2017; 62,826,416 and 49,015,339 shares issued and outstanding at September 30, 2018 and December 31, 2017, respectively	6	5
Additional paid-in capital	521,285	439,048
Accumulated other comprehensive loss	(854)	(963)
Accumulated deficit	(304,884)	(254,062)
Total stockholders’ equity	215,553	184,028
Total liabilities and stockholders' equity	$ 225,907	$ 201,905

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) (Unaudited) - $ / shares	Sep. 30, 2018	Dec. 31, 2017
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	62,826,416	49,015,339
Common stock, shares outstanding	62,826,416	49,015,339

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Collaboration and license revenue	$ 833	$ 463	$ 1,542	$ 1,388
Type of Revenue [Extensible List]	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Operating expenses:
Research and development	$ 14,480	$ 10,272	$ 38,491	$ 27,825
General and administrative	4,826	4,762	19,373	16,815
Impairment of intangible asset	5,000		5,000
Total operating expenses	24,306	15,034	62,864	44,640
Operating loss	(23,473)	(14,571)	(61,322)	(43,252)
Other income, net	1,265	742	3,104	1,894
Net loss before income tax benefit	(22,208)	(13,829)	(58,218)	(41,358)
Income tax benefit	1,250		1,250
Net loss	(20,958)	(13,829)	(56,968)	(41,358)
Other comprehensive loss:
Net unrealized (loss) gain on marketable securities	53	35	129	(102)
Foreign currency translation adjustment		(183)	(21)	(442)
Comprehensive loss	$ (20,905)	$ (13,977)	$ (56,860)	$ (41,902)
Net loss per share -basic and diluted	$ (0.34)	$ (0.32)	$ (0.94)	$ (0.97)
Weighted-average common shares used to compute net loss per share - basic and diluted	62,454	43,381	60,856	42,849

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities:
Net loss	$ (56,968)	$ (41,358)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,361	1,592
Stock-based compensation expense	12,250	6,839
Amortization of premium and accrued interest on marketable securities	199	419
Impairment of intangible asset	5,000
Other	(15)	60
Changes in operating assets and liabilities:
Accounts receivable, net		886
Prepaid expenses and other current assets	(1,518)	(136)
Accounts payable	5	166
Accrued expenses and other current liabilities	353	(208)
Restructuring liabilities		(25)
Deferred revenue	(884)	(1,388)
Deferred rent	233	(70)
Deferred tax liability	(1,250)
Net cash used in operating activities	(41,234)	(33,223)
Cash flows from investing activities:
Purchases of marketable securities	(55,924)	(201,038)
Maturities of marketable securities	117,993	45,061
Purchases of property and equipment	(652)	(918)
Net cash provided by (used in) investing activities	61,417	(156,895)
Cash flows from financing activities:
Proceeds from offerings of common stock, net of issuance costs	70,189
Proceeds from issuance of common stock pursuant to option exercises	687	312
Taxes paid related to net share settlement of restricted stock units	(1,037)	(292)
Proceeds from employee stock purchase plan	149	83
Proceeds from a financing arrangement	100
Repayment of loan	(118)
Net cash provided by financing activities	69,970	103
Effect of foreign currency exchange rate on cash and cash equivalents		(442)
Net increase (decrease) in cash and cash equivalents and restricted cash	90,153	(190,457)
Cash and cash equivalents and restricted cash at beginning of period	70,519	222,170
Cash and cash equivalents and restricted cash at end of period	160,672	31,713
Supplemental schedule of noncash investing and financing information
Unpaid deferred offering costs in accounts payable and accrued expenses		200
Fixed assets in accounts payable, accrued expenses and other current liabilities	$ 278	$ 148

Organization and Basis of Prese

Organization and Basis of Presentation	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Organization and Basis of Presentation	1. Organization and Basis of Presentation Adverum Biotechnologies, Inc. (the “Company”) was incorporated in Delaware on July 17, 2006 as Avalanche Biotechnologies, Inc. and changed its name to Adverum Biotechnologies, Inc. on May 11, 2016. The Company is headquartered in Menlo Park, California. The Company is a gene therapy company targeting unmet medical needs in ophthalmology and rare diseases. Since the Company’s inception, it has devoted its efforts principally to performing research and development activities, including conducting preclinical studies and early clinical trials, filing patent applications, obtaining regulatory agreements, 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 $304.9 million as of September 30, 2018. 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 at least through the first half of 2020. Follow-on Offerings — In February 2018, the Company completed an underwritten public offering for the sale of 10,222,235 shares of its common stock and raised total net proceeds of $64.5 million, after discounts and other issuance costs. In August 2017, the Company entered into an at-the-market sales agreement with an agent for the sales of its common stock at market price (the “2017 stock offering agreement”). In January 2018, the Company issued and sold a total of 1,419,893 shares of its common stock at market prices under the 2017 stock offering agreement and raised total net proceeds of $5.7 million, after issuance costs. 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, 2018, 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, 2017 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 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, 2017 filed with the SEC.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Use of Estimates — The accompanying consolidated financial statements have been prepared in accordance with U.S. GAAP. The preparation of the 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 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, 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. Accounting Standard Updates Recently Adopted Accounting Standard Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers (“Topic 606”), which supersedes the revenue recognition requirements in ASC 605, Revenue Recognition . Effective January 1, 2018, the Company adopted the new revenue standards under Topic 606 using the modified retrospective approach. Results for reporting periods beginning after January 1, 2018 are presented under Topic 606, while prior period results are not adjusted and continue to be reported in accordance with the revenue standards under Topic 605. 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 Regeneron Pharmaceuticals, Inc. (“Regeneron”), Editas Medicine, Inc. (“Editas”), and GenSight Biologics (“GenSight”) are within the scope of Topic 606. Upon the adoption of Topic 606, the Company recorded a net decrease of $6.1 million to its deferred revenue and opening accumulated deficit as of January 1, 2018 for the cumulative effect of the adoption. The effect of the adoption is summarized for the Company’s license and collaboration agreements as follows: Collaboration Agreement with Regeneron — Under Topic 606, the transaction price at contract inception was determined to be $8.0 million, which was related to the non-refundable upfront payment for license and research services. The arrangement also provides for additional payments to the Company when certain development and regulatory 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 at contract inception. The transaction price of $8.0 million at contract inception was allocated to two performance obligations. The Company’s deferred revenue associated with its Regeneron collaboration agreement as of December 31, 2017 under Topic 605 was $6.5 million. As a result of adopting Topic 606, the Company recorded a $6.5 million reduction to its deferred revenue and opening accumulated deficit during the three months ended March 31, 2018 as the performance obligations associated with the Regeneron deferred revenue were satisfied as of January 1, 2018. There was no outstanding deferred revenue associated with Regeneron as of March 31, 2018 or September 30, 2018. 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 arrangement provides for additional payments to the Company when certain development and regulatory 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 at contract inception. The transaction price of $1.0 million at contract inception was allocated to a single performance obligation. The Company’s deferred revenue associated with its Editas collaboration agreement as of December 31, 2017 under Topic 605 was $0.5 million. As a result of adopting Topic 606, the Company recorded an increase of $0.4 million to its deferred revenue and opening accumulated deficit during the three months ended March 31, 2018 due to differences in the timing of recognition under Topic 606. During the three and nine months ended September 30, 2018, the Company recognized revenue of $0.6 million and $1.3 million, respectively, associated with the Editas collaboration agreement. The Company’s deferred revenue balance of $0.1 million as of September 30, 2018 was associated with Editas and is expected to be recognized over a period of one month as the research and development services are performed. 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 three months ended September 30, 2018, GenSight achieved a clinical development milestone pursuant to the agreement. This milestone was previously constrained under Topic Under Topic 605, the Company’s revenue for the three and nine months ended September 30, 2018 would have been $0.5 million and $1.6 million, respectively. Recently Issued and Not Yet Adopted Accounting Pronouncements In February 2016, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2016-2, Leases, which amends the current guidance on leasing activities to provide more transparency and comparability, and requires that all leases be recognized by lessees on their balance sheet as a right-of-use asset and corresponding lease liability, which are currently accounted for as operating leases. The new standard is effective for fiscal years and interim periods within those fiscal years beginning after December 15, 2018, with early adoption permitted. The Company will adopt the new standard using the modified retrospective approach as of January 1, 2019 and will recognize a right of use asset and lease liability on the adoption date. The Company has identified the population of lease agreements and is currently assessing the impact of other arrangements for embedded leases. While the Company continues to evaluate the effect of the standard, the Company anticipates that the adoption will result in a material increase in assets and liabilities on its consolidated balance sheet and will not have a material impact on the consolidated statement of operations or statement of cash flows.

Fair Value Measurements and Fai

Fair Value Measurements and Fair Value of Financial Instruments	9 Months Ended
	Sep. 30, 2018
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 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, 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. In certain cases where there is limited activity or less transparency around inputs to valuation, securities are classified as Level 3 within the valuation hierarchy. The following is a summary of the Company’s cash equivalents and short-term investments: September 30, 2018 Amortized Cost Basis Unrealized Gains Unrealized Loses Estimated Fair Value (In thousands) Level 1: Money market funds $ 125 $ — $ — $ 125 Level 2: U.S. government and agency securities 26,402 — (41 ) 26,361 Commercial paper 166,264 — — 166,264 Corporate bonds 19,844 — (11 ) 19,833 Certificates of deposit 3,994 — — 3,994 Total cash equivalents and short-term investments 216,629 — (52 ) 216,577 Less: cash equivalents (158,368 ) — — (158,368 ) Total short-term investments $ 58,261 $ — $ (52 ) $ 58,209 December 31, 2017 Amortized Cost Basis Unrealized Gains Unrealized Loses Estimated Fair Value (In thousands) Level 1: Money market funds $ 65 $ — $ — $ 65 Level 2: U.S. government and agency securities 58,351 — (145 ) 58,206 Commercial paper 71,427 — — 71,427 Corporate bonds 38,354 1 (38 ) 38,317 Certificates of deposit 9,731 — — 9,731 Total cash equivalents and short-term investments 177,928 1 (183 ) 177,746 Less: cash equivalents (57,780 ) — — (57,780 ) Total short-term investments $ 120,148 $ 1 $ (183 ) $ 119,966 As of September 30, 2018, the fair value of the Company’s financing liability related to The Alpha-1 Project, Inc. (the “TAP financing”) was zero. As of December 31, 2017, the fair value of TAP financing was $0.2 million, which was classified within Level 3 in the fair value hierarchy. The Company elected the fair value option to account for this financing arrangement. The fair value of the financing arrangement was determined based on the expected value approach and is classified as Level 3 within the fair value hierarchy. The key unobservable inputs in the valuation model include timing of milestones, probability of achievement of development and commercial milestones, and a discount factor. There were no transfers within the hierarchy during the three and nine months ended September 30, 2018. The Company’s marketable securities as of September 30, 2018 mature within one year. Management regularly reviews all of the Company’s investments for other-than-temporary declines in estimated fair value. Management’s review includes the 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 management 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. Management determined that the gross unrealized losses of $0.1 million on the Company’s marketable securities as of September 30, 2018 were temporary in nature. Therefore, none of the Company’s marketable securities were other-than-temporarily impaired as of September 30, 2018.

Significant Agreements

Significant Agreements	9 Months Ended
	Sep. 30, 2018
Research And Development [Abstract]
Significant Agreements	4. Significant Agreements Editas— In January 2018, the Company entered into an agreement to amend its collaboration, option and license agreement with Editas. The Company originally entered into an agreement with Editas in August 2016 pursuant to which the Company and Editas collaborate on certain studies using AAV vectors in connection with Editas’ genome editing technology and the Company grants to Editas an exclusive option to obtain certain exclusive rights to use the Company’s proprietary vectors in up to five ophthalmic indications. In January 2018, the Company and Editas extended the research collaboration, option and license agreement. In consideration for extending the agreement, Editas made a one-time, non-refundable cash payment of $0.5 million to the Company in February 2018. In June 2018, the Company and Editas entered into a subsequent amendment to the agreement to extend the Research Period and First Option Exercise Date (each as defined in the collaboration, option, and license agreement with Editas, as amended). Under the terms of the agreement, as amended, Editas may exercise the option with respect to a designated initial indication until November 16, 2018. With respect to the four other indications, Editas may exercise the option until August 8, 2020, provided that the option will expire on August 8, 2019 if Editas has not exercised the option with respect to the initial indication or any other indication by such date. Upon Editas’ timely exercise of the option with respect to the designated initial indication, Editas will pay the Company a $1.3 million fee. For the first additional indication for which Editas timely exercises its option, Editas will pay the Company a $1.5 million fee. Upon each subsequent exercise of the option, Editas will pay the Company a $1.0 million fee per indication. If Editas elects to develop a product using certain of the Company’s proprietary vectors, the Company will be eligible to receive up to $15.5 million in development and commercialization milestone payments for such product, and tiered royalties between the mid-single digits and low teens on net sales of such product, subject to certain adjustments. Unless earlier terminated, the agreement will be in effect until the later of the expiration of the option exercise period or the expiration of the royalty term of the last product. At any time after the option is first exercised, Editas may terminate the agreement for convenience in its entirety or on an indication-by-indication or country-by-country basis, upon prior written notice to the Company. The Company may also terminate the agreement if Editas challenges the Company’s patents relating to its proprietary vectors and does not withdraw such challenge within a defined period of time. In addition, either party may terminate the agreement with written notice upon a bankruptcy of the other party or upon an uncured material breach by the other party. Under Topic 606, the transaction price is $1.5 million related to 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 arrangement provides for additional payments to the Company when certain development and regulatory 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 $1.5 million was allocated to a single performance obligation, research and development. During the three and nine months ended September 30, 2018, the Company recognized revenue of $0.6 million and $1.3 million, respectively, associated with the Editas collaboration agreement. The Company’s deferred revenue balance of $0.1 million as of September 30, 2018 was associated with Editas and is expected to be recognized over a period of one month as the research and development services are performed.

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	9 Months Ended
	Sep. 30, 2018
Payables And Accruals [Abstract]
Accrued Expenses and Other Current Liabilities	5. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consist of the following: September 30, 2018 December (In thousands) Accrued professional services $ 2,359 $ 2,295 Employee compensation 2,852 2,259 Accrued preclinical, clinical and process development costs 1,973 2,165 Other 593 245 Total accrued expenses and other current liabilities $ 7,777 $ 6,964

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2018
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	6. Commitments and Contingencies Leases On June 28, 2018, the Company entered into a lease on a new facility with office, laboratory, and manufacturing space, which will serve as the Company’s new corporate headquarters. The term of the lease is ten years and also provides for two options to extend the lease term for a period of seven years each. The Company is obligated to make lease payments totaling approximately $49.3 million over the initial term of the lease. Under the lease, the Company will receive a tenant improvement allowance for the costs associated with the design, development and construction of tenant improvements for the leased facility. 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 balance sheet. As of September 30, 2018, the aggregate future minimum payments under the Company’s leases are as follows: Year ending December 31, Future Commitments (In thousands) 2018 (remaining 3 months) $ 294 2019 3,344 2020 4,221 2021 4,683 2022 4,846 Thereafter 33,853 Total minimum lease payments $ 51,241 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. There have been no material changes from the legal proceedings described in our quarterly report on Form 10-Q for the period ended June 30, 2018.

Equity Incentive Awards

Equity Incentive Awards	9 Months Ended
	Sep. 30, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Equity Incentive Awards	7. Equity Incentive Awards The following table summarizes the Company’s option activity and related information: Number of Options (in thousands) Weighted- Average Exercise Price Weighted- Average Remaining Contractual Life (in years) Aggregate Intrinsic Value (in thousands) Balance at December 31, 2017 6,695 $ 4.51 Options granted 1,709 6.29 Options exercised (1,596 ) 0.43 Options cancelled (520 ) 6.05 Balance at September 30, 2018 6,288 $ 5.90 7.8 $ 13,001 Exercisable as of September 30, 2018 3,016 $ 6.83 7.0 $ 7,745 Restricted Stock Units (“RSUs”) The following table summarizes the Company’s RSUs activity and related information: Number of Units (in thousands) Weighted- Average Grant- Date Fair Value Weighted- Average Remaining Contractual Term (in years) Outstanding at December 31, 2017 2,515 $ 3.24 1.6 Granted 1,331 6.00 Vested and released (672 ) 3.38 Forfeited (517 ) 8.01 Outstanding at September 30, 2018 2,657 $ 3.66 1.7 Stock-Based Compensation Expense The following table presents, by operating expense, the Company’s stock-based compensation expense: Three Months Ended Nine Months Ended September 30, September 30, 2018 2017 2018 2017 (In thousands) Research and development $ 1,693 $ 1,698 $ 4,892 $ 4,335 General and administrative 1,303 1,002 7,358 2,504 Total stock-based compensation expense $ 2,996 $ 2,700 $ 12,250 $ 6,839 During the nine months ended September 30, 2018, the Company recorded approximately $4.1 million of stock-based compensation expense as a result of the modification of the vesting and exercisability of stock awards associated with the departure of two of its executives.

Net Loss per Share

Net Loss per Share	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
Net Loss per Share	8. 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, 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. The Company excluded approximately 9.1 million and 10.0 million shares of potentially dilutive securities as of September 30, 2018 and 2017, respectively, from the computations of diluted weighted-shares outstanding because their effect would be anti-dilutive.

Impairment of Intangible Asset

Impairment of Intangible Asset	9 Months Ended
	Sep. 30, 2018
Goodwill And Intangible Assets Disclosure [Abstract]
Impairment of Intangible Asset	9. Impairment of Intangible Asset The Company recorded In-process Research and Development ("IPR&D") intangible assets upon the acquisition of Annapurna in May 2016. The carrying value of the IPR&D intangible asset was $5.0 million as of June 30, 2018. The Company evaluates indefinite lived intangible assets for impairment on an annual basis or more frequently if indicators of impairment exist. During the three months ended September 30, 2018, the Company identified an impairment indicator related to the intangible asset and performed an impairment analysis. On October 30, 2018, the Company decided to discontinue the development of ADVM-043. The Company recorded an impairment charge of $5.0 million on IPR&D assets related to the Company’s intangible asset for ADVM-043. This amount was recorded in Impairment of intangible assets on the Company’s condensed consolidated statements of operations and comprehensive loss. In connection with this impairment charge, the Company derecognized $1.3 million of the deferred tax liability related to the intangible asset for ADVM-043. This amount was recorded as income tax benefit on the Company’s condensed consolidated statements of operations and comprehensive loss.

Summary of significant accoun_2

Summary of significant accounting policies (Policies)	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates — The accompanying consolidated financial statements have been prepared in accordance with U.S. GAAP. The preparation of the 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 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, 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.
Accounting Standard Update Recently Adopted	Accounting Standard Updates Recently Adopted Accounting Standard Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers (“Topic 606”), which supersedes the revenue recognition requirements in ASC 605, Revenue Recognition . Effective January 1, 2018, the Company adopted the new revenue standards under Topic 606 using the modified retrospective approach. Results for reporting periods beginning after January 1, 2018 are presented under Topic 606, while prior period results are not adjusted and continue to be reported in accordance with the revenue standards under Topic 605. 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 Regeneron Pharmaceuticals, Inc. (“Regeneron”), Editas Medicine, Inc. (“Editas”), and GenSight Biologics (“GenSight”) are within the scope of Topic 606. Upon the adoption of Topic 606, the Company recorded a net decrease of $6.1 million to its deferred revenue and opening accumulated deficit as of January 1, 2018 for the cumulative effect of the adoption. The effect of the adoption is summarized for the Company’s license and collaboration agreements as follows: Collaboration Agreement with Regeneron — Under Topic 606, the transaction price at contract inception was determined to be $8.0 million, which was related to the non-refundable upfront payment for license and research services. The arrangement also provides for additional payments to the Company when certain development and regulatory 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 at contract inception. The transaction price of $8.0 million at contract inception was allocated to two performance obligations. The Company’s deferred revenue associated with its Regeneron collaboration agreement as of December 31, 2017 under Topic 605 was $6.5 million. As a result of adopting Topic 606, the Company recorded a $6.5 million reduction to its deferred revenue and opening accumulated deficit during the three months ended March 31, 2018 as the performance obligations associated with the Regeneron deferred revenue were satisfied as of January 1, 2018. There was no outstanding deferred revenue associated with Regeneron as of March 31, 2018 or September 30, 2018. 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 arrangement provides for additional payments to the Company when certain development and regulatory 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 at contract inception. The transaction price of $1.0 million at contract inception was allocated to a single performance obligation. The Company’s deferred revenue associated with its Editas collaboration agreement as of December 31, 2017 under Topic 605 was $0.5 million. As a result of adopting Topic 606, the Company recorded an increase of $0.4 million to its deferred revenue and opening accumulated deficit during the three months ended March 31, 2018 due to differences in the timing of recognition under Topic 606. During the three and nine months ended September 30, 2018, the Company recognized revenue of $0.6 million and $1.3 million, respectively, associated with the Editas collaboration agreement. The Company’s deferred revenue balance of $0.1 million as of September 30, 2018 was associated with Editas and is expected to be recognized over a period of one month as the research and development services are performed. 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 three months ended September 30, 2018, GenSight achieved a clinical development milestone pursuant to the agreement. This milestone was previously constrained under Topic Under Topic 605, the Company’s revenue for the three and nine months ended September 30, 2018 would have been $0.5 million and $1.6 million, respectively.
Recently-Issued and Not Yet Adopted Accounting Pronouncements	Recently Issued and Not Yet Adopted Accounting Pronouncements In February 2016, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2016-2, Leases, which amends the current guidance on leasing activities to provide more transparency and comparability, and requires that all leases be recognized by lessees on their balance sheet as a right-of-use asset and corresponding lease liability, which are currently accounted for as operating leases. The new standard is effective for fiscal years and interim periods within those fiscal years beginning after December 15, 2018, with early adoption permitted. The Company will adopt the new standard using the modified retrospective approach as of January 1, 2019 and will recognize a right of use asset and lease liability on the adoption date. The Company has identified the population of lease agreements and is currently assessing the impact of other arrangements for embedded leases. While the Company continues to evaluate the effect of the standard, the Company anticipates that the adoption will result in a material increase in assets and liabilities on its consolidated balance sheet and will not have a material impact on the consolidated statement of operations or statement of cash flows.

Fair Value Measurements and F_2

Fair Value Measurements and Fair Value of Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2018
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, 2018 Amortized Cost Basis Unrealized Gains Unrealized Loses Estimated Fair Value (In thousands) Level 1: Money market funds $ 125 $ — $ — $ 125 Level 2: U.S. government and agency securities 26,402 — (41 ) 26,361 Commercial paper 166,264 — — 166,264 Corporate bonds 19,844 — (11 ) 19,833 Certificates of deposit 3,994 — — 3,994 Total cash equivalents and short-term investments 216,629 — (52 ) 216,577 Less: cash equivalents (158,368 ) — — (158,368 ) Total short-term investments $ 58,261 $ — $ (52 ) $ 58,209 December 31, 2017 Amortized Cost Basis Unrealized Gains Unrealized Loses Estimated Fair Value (In thousands) Level 1: Money market funds $ 65 $ — $ — $ 65 Level 2: U.S. government and agency securities 58,351 — (145 ) 58,206 Commercial paper 71,427 — — 71,427 Corporate bonds 38,354 1 (38 ) 38,317 Certificates of deposit 9,731 — — 9,731 Total cash equivalents and short-term investments 177,928 1 (183 ) 177,746 Less: cash equivalents (57,780 ) — — (57,780 ) Total short-term investments $ 120,148 $ 1 $ (183 ) $ 119,966

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	9 Months Ended
	Sep. 30, 2018
Payables And Accruals [Abstract]
Schedule of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consist of the following: September 30, 2018 December (In thousands) Accrued professional services $ 2,359 $ 2,295 Employee compensation 2,852 2,259 Accrued preclinical, clinical and process development costs 1,973 2,165 Other 593 245 Total accrued expenses and other current liabilities $ 7,777 $ 6,964

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2018
Commitments And Contingencies Disclosure [Abstract]
Schedule of Future Minimum Payments under Lease	As of September 30, 2018, the aggregate future minimum payments under the Company’s leases are as follows: Year ending December 31, Future Commitments (In thousands) 2018 (remaining 3 months) $ 294 2019 3,344 2020 4,221 2021 4,683 2022 4,846 Thereafter 33,853 Total minimum lease payments $ 51,241

Equity Incentive Awards (Tables

Equity Incentive Awards (Tables)	9 Months Ended
	Sep. 30, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Stock Options Activity	The following table summarizes the Company’s option activity and related information: Number of Options (in thousands) Weighted- Average Exercise Price Weighted- Average Remaining Contractual Life (in years) Aggregate Intrinsic Value (in thousands) Balance at December 31, 2017 6,695 $ 4.51 Options granted 1,709 6.29 Options exercised (1,596 ) 0.43 Options cancelled (520 ) 6.05 Balance at September 30, 2018 6,288 $ 5.90 7.8 $ 13,001 Exercisable as of September 30, 2018 3,016 $ 6.83 7.0 $ 7,745
Summary of Restricted Stock Units Activity	The following table summarizes the Company’s RSUs activity and related information: Number of Units (in thousands) Weighted- Average Grant- Date Fair Value Weighted- Average Remaining Contractual Term (in years) Outstanding at December 31, 2017 2,515 $ 3.24 1.6 Granted 1,331 6.00 Vested and released (672 ) 3.38 Forfeited (517 ) 8.01 Outstanding at September 30, 2018 2,657 $ 3.66 1.7
Stock-Based Compensation Expense	The following table presents, by operating expense, the Company’s stock-based compensation expense: Three Months Ended Nine Months Ended September 30, September 30, 2018 2017 2018 2017 (In thousands) Research and development $ 1,693 $ 1,698 $ 4,892 $ 4,335 General and administrative 1,303 1,002 7,358 2,504 Total stock-based compensation expense $ 2,996 $ 2,700 $ 12,250 $ 6,839

Organization and Basis of Pre_2

Organization and Basis of Presentation - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended		9 Months Ended
	Feb. 28, 2018	Jan. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Date of incorporation			Jul. 17, 2006
Change of entity name date			May 11, 2016
Accumulated deficit			$ (304,884)	$ (254,062)
Net proceeds from issuance of common stock			$ 70,189
Underwritten Public Offering [Member]
Class of Stock [Line Items]
Issuance of common stock	10,222,235
Net proceeds from issuance of common stock	$ 64,500
2017 Stock Offering Agreement [Member]
Class of Stock [Line Items]
Issuance of common stock		1,419,893	0
Net proceeds from issuance of common stock		$ 5,700

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended			3 Months Ended		9 Months Ended
	Feb. 28, 2018	Aug. 31, 2016	May 31, 2014	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Summary Of Significant Accounting Policies [Line Items]
Retained earnings (accumulated deficit)				$ (304,884)		$ (304,884)				$ (254,062)
Collaboration and license revenue				$ 833	$ 463	$ 1,542	$ 1,388
Type of Revenue [Extensible List]				us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Editas Medicine Inc [Member]
Summary Of Significant Accounting Policies [Line Items]
Initial payments received	$ 500
Collaboration and license revenue				$ 600		$ 1,300
Type of Revenue [Extensible List]				us-gaap:LicenseAndServiceMember		us-gaap:LicenseAndServiceMember
Deferred revenue, current portion				$ 100		$ 100
Revenue recognition, expected time period				1 month		1 month
Regeneron Corporation [Member]
Summary Of Significant Accounting Policies [Line Items]
Deferred revenue				$ 0		$ 0		$ 0
Accounting Standards Update 2014-09 [Member] | Editas Medicine Inc [Member]
Summary Of Significant Accounting Policies [Line Items]
Initial payments received	$ 500
Collaboration and license revenue				$ 600		$ 1,300
Type of Revenue [Extensible List]				us-gaap:LicenseAndServiceMember		us-gaap:LicenseAndServiceMember
Deferred revenue, current portion				$ 100		$ 100
Revenue recognition, expected time period				1 month		1 month
Accounting Standards Update 2014-09 [Member] | Upfront Payment Arrangement [Member] | Editas Medicine Inc [Member]
Summary Of Significant Accounting Policies [Line Items]
Deferred revenue		$ 1,000
Initial payments received		$ 1,000
Accounting Standards Update 2014-09 [Member] | Regeneron Corporation [Member] | Upfront Payment Arrangement [Member]
Summary Of Significant Accounting Policies [Line Items]
Deferred revenue			$ 8,000
Initial payments received			$ 8,000
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Summary Of Significant Accounting Policies [Line Items]
Retained earnings (accumulated deficit)									$ 6,100
Deferred revenue									$ (6,100)
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member] | Editas Medicine Inc [Member]
Summary Of Significant Accounting Policies [Line Items]
Retained earnings (accumulated deficit)								(400)
Deferred revenue								400
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member] | Regeneron Corporation [Member]
Summary Of Significant Accounting Policies [Line Items]
Retained earnings (accumulated deficit)								6,500
Deferred revenue								$ (6,500)
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Editas Medicine Inc [Member]
Summary Of Significant Accounting Policies [Line Items]
Collaboration and license revenue				$ 500		$ 1,600
Type of Revenue [Extensible List]				us-gaap:LicenseAndServiceMember		us-gaap:LicenseAndServiceMember
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | GenSight Biologics [Member] | License Agreement [Member]
Summary Of Significant Accounting Policies [Line Items]
Collaboration and license revenue				$ 200
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Accounting Standards Update 2014-09 [Member] | Editas Medicine Inc [Member]
Summary Of Significant Accounting Policies [Line Items]
Deferred revenue										500
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Accounting Standards Update 2014-09 [Member] | Regeneron Corporation [Member]
Summary Of Significant Accounting Policies [Line Items]
Deferred revenue										$ 6,500

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, 2018	Dec. 31, 2017
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	$ 58,261	$ 120,148
Unrealized Gains		1
Unrealized Loses	(52)	(183)
Estimated Fair Value	58,209	119,966
Less: Cash Equivalents, Amortized Cost Basis	(158,368)	(57,780)
Less: Cash Equivalents, Unrealized Gains	0	0
Less: Cash Equivalents, Unrealized Loses	0	0
Less: Cash Equivalents, Estimated Fair Value	(158,368)	(57,780)
Money Market Funds [Member] | Quoted Prices in Active Markets (Level 1) [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	125	65
Estimated Fair Value	125	65
Certificates of Deposit [Member] | Significant Other Observable Inputs (Level 2) [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	3,994	9,731
Estimated Fair Value	3,994	9,731
Commercial Paper [Member] | Significant Other Observable Inputs (Level 2) [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	166,264	71,427
Estimated Fair Value	166,264	71,427
U.S. Government Agency Securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	26,402	58,351
Unrealized Loses	(41)	(145)
Estimated Fair Value	26,361	58,206
Corporate Bonds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	19,844	38,354
Unrealized Gains		1
Unrealized Loses	(11)	(38)
Estimated Fair Value	19,833	38,317
Total Cash Equivalents and Short-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	216,629	177,928
Unrealized Gains		1
Unrealized Loses	(52)	(183)
Estimated Fair Value	$ 216,577	$ 177,746

Fair Value Measurements and F_4

Fair Value Measurements and Fair Value of Financial Instruments - Additional Information (Detail) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Liabilities transferred within Level 3	$ 0	$ 0
Gross unrealized losses on available-for-sale-securities temporary	100,000	100,000
Marketable securities other-than-temporarily impaired	0	0
The Alpha-1 Project, Inc. [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of financing liability	$ 0	$ 0	$ 200,000

Significant Agreements - Additi

Significant Agreements - Additional Information (Detail) - USD ($)	1 Months Ended		3 Months Ended		9 Months Ended
	Feb. 28, 2018	Aug. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
License Agreement [Line Items]
Revenue recognized			$ 833,000	$ 463,000	$ 1,542,000	$ 1,388,000
Type of Revenue [Extensible List]			us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Editas Medicine Inc [Member]
License Agreement [Line Items]
Initial payments received	$ 500,000
Collaboration, option and license agreement fee receivable per indication		$ 1,000,000
Range of tiered royalties receivable on net sales					between the mid-single digits and low teens
Revenue recognized			$ 600,000		$ 1,300,000
Type of Revenue [Extensible List]			us-gaap:LicenseAndServiceMember		us-gaap:LicenseAndServiceMember
Deferred revenue			$ 100,000		$ 100,000
Revenue recognition, expected time period			1 month		1 month
Editas Medicine Inc [Member] | Topic 606 [Member]
License Agreement [Line Items]
Initial payments received	$ 500,000
Collaboration, option and license agreement fee receivable per indication		1,500,000
Non-refundable upfront payment received		1,000,000
Revenue recognized			$ 600,000		$ 1,300,000
Type of Revenue [Extensible List]			us-gaap:LicenseAndServiceMember		us-gaap:LicenseAndServiceMember
Deferred revenue			$ 100,000		$ 100,000
Revenue recognition, expected time period			1 month		1 month
Editas Medicine Inc [Member] | Initial Indication [Member]
License Agreement [Line Items]
Collaboration, option and license agreement fee receivable per indication		1,300,000
Editas Medicine Inc [Member] | Additional Indication [Member]
License Agreement [Line Items]
Collaboration, option and license agreement fee receivable per indication		1,500,000
Editas Medicine Inc [Member] | Maximum [Member]
License Agreement [Line Items]
Potential milestone earnings		$ 15,500,000

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities - Schedule of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Accrued Expenses And Other Current Liabilities [Abstract]
Accrued professional services	$ 2,359	$ 2,295
Employee compensation	2,852	2,259
Accrued preclinical, clinical and process development costs	1,973	2,165
Other	593	245
Total accrued expenses and other current liabilities	$ 7,777	$ 6,964

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2018USD ($)
Other Commitments [Line Items]
Total minimum lease payments	$ 51,241
Restricted cash, noncurrent	999
Letter of Credit [Member]
Other Commitments [Line Items]
Security deposit	$ 1,000
New Corporate Headquarters [Member]
Other Commitments [Line Items]
Lease entered date	Jun. 28, 2018
Lease term	10 years
Lease renewal term	7 years
Lease description	The term of the lease is ten years and also provides for two options to extend the lease term for a period of seven years each.
Total minimum lease payments	$ 49,300

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Future Minimum Payments under Lease (Detail) $ in Thousands	Sep. 30, 2018USD ($)
Commitments And Contingencies Disclosure [Abstract]
2018 (remaining 3 months)	$ 294
2,019	3,344
2,020	4,221
2,021	4,683
2,022	4,846
Thereafter	33,853
Total minimum lease payments	$ 51,241

Equity Incentive Awards - Summa

Equity Incentive Awards - Summary of Stock Options Activity (Detail) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2018USD ($)$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Options Outstanding [Roll Forward]
Number of Options, Beginning Balance | shares	6,695,000
Number of Options, Options granted | shares	1,709,000
Number of Options, Options exercised | shares	(1,596,000)
Number of Options, Options cancelled | shares	(520,000)
Number of Options, Ending Balance | shares	6,288,000
Number of Options, Exercisable | shares	3,016,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted-Average Exercise Price, Beginning Balance | $ / shares	$ 4.51
Weighted-Average Exercise Price, Options granted | $ / shares	6.29
Weighted-Average Exercise Price, Options exercised | $ / shares	0.43
Weighted-Average Exercise Price, Options cancelled | $ / shares	6.05
Weighted-Average Exercise Price, Ending Balance | $ / shares	5.90
Weighted-Average Exercise Price, Exercisable | $ / shares	$ 6.83
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted-Average Remaining Contractual Life (In years)	7 years 9 months 18 days
Weighted-Average Remaining Contractual Life (In years), Exercisable	7 years
Aggregate Intrinsic Value, Options outstanding | $	$ 13,001
Aggregate Intrinsic Value, Exercisable | $	$ 7,745

Equity Incentive Awards - Sum_2

Equity Incentive Awards - Summary of Restricted Stock Units Activity (Detail) - Restricted Stock Units [Member] - $ / shares	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Units, Beginning Balance	2,515,000
Number of Units, Granted	1,331,000
Number of Units, Vested and released	(672,000)
Number of Units, Forfeited	(517,000)
Number of Units, Ending Balance	2,657,000	2,515,000
Weighted-Average Grant-Date Fair Value, Beginning Balance	$ 3.24
Weighted-Average Grant-Date Fair Value, Granted	6
Weighted-Average Grant-Date Fair Value, Vested and released	3.38
Weighted-Average Grant-Date Fair Value, Forfeited	8.01
Weighted-Average Grant-Date Fair Value, Ending Balance	$ 3.66	$ 3.24
Weighted-Average Remaining Contractual Term (In years)	1 year 8 months 12 days	1 year 7 months 6 days

Equity Incentive Awards - Stock

Equity Incentive Awards - Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 2,996	$ 2,700	$ 12,250	$ 6,839
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	1,693	1,698	4,892	4,335
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 1,303	$ 1,002	$ 7,358	$ 2,504

Equity Incentive Awards - Addit

Equity Incentive Awards - Additional Information (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)Executive	Sep. 30, 2017USD ($)
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 2,996	$ 2,700	$ 12,250	$ 6,839
Number of departure executives | Executive			2
Departure of Executives [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense			$ 4,100

Net Loss per Share - Additional

Net Loss per Share - Additional Information (Detail) - shares shares in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Antidilutive common stock equivalents excluded from calculation of diluted net loss per share	9.1	10

Impairment of Intangible Asset

Impairment of Intangible Asset - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Finite Lived Intangible Assets [Line Items]
Intangible asset				$ 5,000
Impairment charge	$ 5,000	$ 5,000
Deferred tax liability		$ (1,250)
Annapurna Therapeutics SAS [Member] | IPR&D [Member]
Finite Lived Intangible Assets [Line Items]
Intangible asset			$ 5,000
Impairment charge	5,000
Deferred tax liability	$ 1,300