REGENXBIO (RGNX) 10-Q 4 Nov 20 2020 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2020	Oct. 30, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Trading Symbol	RGNX
Entity Registrant Name	REGENXBIO Inc.
Entity Central Index Key	0001590877
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity File Number	001-37553
Entity Tax Identification Number	47-1851754
Entity Address, Address Line One	9600 Blackwell Road
Entity Address, Address Line Two	Suite 210
Entity Address, City or Town	Rockville
Entity Address, State or Province	MD
Entity Address, Postal Zip Code	20850
City Area Code	240
Local Phone Number	552-8181
Entity Common Stock, Shares Outstanding		37,408,448
Document Transition Report	false
Document Quarterly Report	true
Entity Interactive Data Current	Yes
Security Exchange Name	NASDAQ
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Entity Incorporation, State or Country Code	DE

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Current assets
Cash and cash equivalents	$ 93,220	$ 69,514
Marketable securities	148,305	226,696
Accounts receivable, net	122,116	38,148
Prepaid expenses	16,112	6,475
Other current assets	7,197	4,199
Total current assets	386,950	345,032
Marketable securities	48,272	103,785
Accounts receivable, net	3,564	4,155
Property and equipment, net	38,871	28,973
Operating lease right-of-use assets	57,827	10,078
Restricted cash	1,330	1,330
Other assets	4,360	4,555
Total assets	541,174	497,908
Current liabilities
Accounts payable	15,244	6,409
Accrued expenses and other current liabilities	44,356	24,846
Deferred revenue	449
Operating lease liabilities	3,564	2,421
Total current liabilities	63,613	33,676
Deferred revenue	3,895	3,333
Operating lease liabilities	57,461	8,874
Other liabilities	545	1,828
Total liabilities	125,514	47,711
Stockholders’ equity
Preferred stock; $0.0001 par value; 10,000 shares authorized, and no shares issued and outstanding at September 30, 2020 and December 31, 2019
Common stock; $0.0001 par value; 100,000 shares authorized at March 31, 2020 and December 31, 2019; 37,190 and 36,992 shares issued and outstanding at March 31, 2020 and December 31, 2019, respectively	4	4
Additional paid-in capital	658,224	627,810
Accumulated other comprehensive income	263	205
Accumulated deficit	(242,831)	(177,822)
Total stockholders’ equity	415,660	450,197
Total liabilities and stockholders’ equity	$ 541,174	$ 497,908

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	37,404,000	36,992,000
Common stock, shares outstanding	37,404,000	36,992,000

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenues
Revenues	$ 98,912	$ 14,700	$ 133,122	$ 23,465
Types of Revenue[Extensible List]	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Operating Expenses
Cost of revenues	$ 17,364	$ 2,494	$ 25,457	$ 4,450
Research and development	43,968	35,692	119,114	90,378
General and administrative	15,859	12,402	46,246	37,365
Provision for credit losses and other	7,770	8	7,887	(54)
Total operating expenses	84,961	50,596	198,704	132,139
Income (loss) from operations	13,951	(35,896)	(65,582)	(108,674)
Other Income (Loss)
Interest income from licensing	1,444	716	4,141	2,091
Investment income (loss)	(6,607)	431	(4,071)	37,950
Total other income (loss)	(5,163)	1,147	70	40,041
Income (loss) before income taxes	8,788	(34,749)	(65,512)	(68,633)
Income Tax Benefit	3	165	503	364
Net income (loss)	8,791	(34,584)	(65,009)	(68,269)
Other Comprehensive Income (Loss)
Unrealized gain (loss) on available-for-sale securities, net	(487)	(108)	58	1,043
Total other comprehensive income (loss)	(487)	(108)	58	1,043
Comprehensive income (loss)	$ 8,304	$ (34,692)	$ (64,951)	$ (67,226)
Net income (loss) per share:
Basic	$ 0.24	$ (0.94)	$ (1.75)	$ (1.86)
Diluted	$ 0.23	$ (0.94)	$ (1.75)	$ (1.86)
Weighted-average common shares outstanding:
Basic	37,342	36,813	37,234	36,618
Diluted	38,877	36,813	37,234	36,618

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Cumulative Effect Period Of Adoption Adjustment [Member]	Common Stock [Member]	Additional paid in capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Other Comprehensive Income (Loss) [Member]Cumulative Effect Period Of Adoption Adjustment [Member]	Accumulated Deficit [Member]	Accumulated Deficit [Member]Cumulative Effect Period Of Adoption Adjustment [Member]
Balances at Dec. 31, 2018	$ 508,848		$ 4	$ 592,580	$ (720)		$ (83,016)
Balances (ASU 2016-02 (Topic 842) [Member]) at Dec. 31, 2018		$ (33)						$ (33)
Balances (ASU 2018-02 [Member]) at Dec. 31, 2018						$ 40		$ (40)
Balances (Shares) at Dec. 31, 2018			36,120
Exercise of stock options	5,513			5,513
Exercise of stock options, Shares			684
Issuance of common stock under employee stock purchase plan	1,314			1,314
Issuance of common stock under employee stock purchase plan, shares			36
Stock-based compensation expense	19,979			19,979
Unrealized gain (loss) on available-for-sale securities, net	1,043				1,043
Net income (loss)	(68,269)						(68,269)
Balances at Sep. 30, 2019	468,395		$ 4	619,386	363		(151,358)
Balances (Shares) at Sep. 30, 2019			36,840
Balances at Jun. 30, 2019	494,592		$ 4	610,891	471		(116,774)
Balances (Shares) at Jun. 30, 2019			36,752
Exercise of stock options	384			384
Exercise of stock options, Shares			62
Issuance of common stock under employee stock purchase plan	949			949
Issuance of common stock under employee stock purchase plan, shares			26
Stock-based compensation expense	7,162			7,162
Unrealized gain (loss) on available-for-sale securities, net	(108)				(108)
Net income (loss)	(34,584)						(34,584)
Balances at Sep. 30, 2019	468,395		$ 4	619,386	363		(151,358)
Balances (Shares) at Sep. 30, 2019			36,840
Balances at Dec. 31, 2019	450,197		$ 4	627,810	205		(177,822)
Balances (Shares) at Dec. 31, 2019			36,992
Exercise of stock options	4,247			4,247
Exercise of stock options, Shares			356
Issuance of common stock under employee stock purchase plan	1,799			1,799
Issuance of common stock under employee stock purchase plan, shares			55
Stock-based compensation expense	24,368			24,368
Unrealized gain (loss) on available-for-sale securities, net	58				58
Net income (loss)	(65,009)						(65,009)
Balances at Sep. 30, 2020	415,660		$ 4	658,224	263		(242,831)
Balances (Shares) at Sep. 30, 2020			37,404
Balances at Jun. 30, 2020	397,861		$ 4	648,729	750		(251,622)
Balances (Shares) at Jun. 30, 2020			37,291
Exercise of stock options	268			268
Exercise of stock options, Shares			74
Issuance of common stock under employee stock purchase plan	1,192			1,192
Issuance of common stock under employee stock purchase plan, shares			38
Stock-based compensation expense	8,035			8,035
Unrealized gain (loss) on available-for-sale securities, net	(487)				(487)
Net income (loss)	8,791						8,791
Balances at Sep. 30, 2020	$ 415,660		$ 4	$ 658,224	$ 263		$ (242,831)
Balances (Shares) at Sep. 30, 2020			37,404

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities
Net loss	$ (65,009)	$ (68,269)
Adjustments to reconcile net loss to net cash used in operating activities
Stock-based compensation expense	24,368	19,979
Depreciation and amortization	6,302	5,229
Provision for credit losses	7,678	0
Net amortization of premiums (accretion of discounts) on marketable debt securities	586	(1,085)
Net realized and unrealized losses (gains) on marketable securities	8,207	(29,440)
Imputed interest income from licensing	(2,033)	(2,091)
Other non-cash adjustments	263	357
Changes in operating assets and liabilities
Accounts receivable	(89,442)	(10,699)
Prepaid expenses	(9,637)	(1,418)
Other current assets	(2,998)	1,286
Operating lease right-of-use assets	1,986	1,712
Other assets	1,318	(2,150)
Accounts payable	9,907	5,339
Accrued expenses and other current liabilities	18,400	1,990
Deferred revenue		(600)
Operating lease liabilities	(2,222)	(1,832)
Other liabilities	(1,203)	(507)
Net cash used in operating activities	(93,529)	(82,199)
Cash flows from investing activities
Purchases of marketable debt securities	(79,374)	(127,925)
Maturities of marketable debt securities	189,882	218,019
Sales of marketable debt securities	2,287
Sales of marketable equity securities	12,374
Purchases of property and equipment	(13,980)	(10,689)
Net cash provided by investing activities	111,189	79,405
Cash flows from financing activities
Proceeds from exercise of stock options	4,247	5,513
Proceeds from issuance of common stock under employee stock purchase plan	1,799	1,314
Net cash provided by financing activities	6,046	6,827
Net increase in cash and cash equivalents and restricted cash	23,706	4,033
Cash and cash equivalents and restricted cash
Beginning of period	70,844	76,614
End of period	94,550	$ 80,647
Supplemental disclosures of non-cash investing and financing activities
Additions to property and equipment through accounts payable and accrued expenses	46
Non-cash additions to property and equipment through tenant improvement allowance	2,217
Non-cash consideration received for licenses granted	$ 1,123

Nature of Business

Nature of Business	9 Months Ended
	Sep. 30, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Nature of Business	1. Nature of Business REGENXBIO Inc. (the Company) is a clinical-stage biotechnology company seeking to improve lives through the curative potential of gene therapy. The Company’s proprietary adeno-associated virus (AAV) gene delivery platform (NAV Technology Platform) consists of exclusive rights to over 100 novel AAV vectors, including AAV7, AAV8, AAV9 and AAVrh10. The NAV® Technology Platform is being applied by the Company, as well as by third-party licensees (NAV Technology Licensees), in the development of a broad pipeline of product candidates in multiple therapeutic areas and in one commercially available product, Zolgensma®, which is marketed by a NAV Technology Licensee. The Company was formed in 2008 in the State of Delaware and is headquartered in Rockville, Maryland. Liquidity and Risks As of September 30, 2020, the Company had generated an accumulated deficit of $242.8 million since inception. As the Company has incurred cumulative losses since inception, transition to recurring profitability is dependent upon achieving a level of revenues adequate to support the Company’s cost structure, which depends heavily on the successful development, approval and commercialization of its product candidates. The Company may never achieve recurring profitability, and unless and until it does, the Company will continue to need to raise additional capital, to the extent possible. As of September 30, 2020, the Company had cash, cash equivalents and marketable securities of $289.8 million, which management believes is sufficient to fund operations for at least the next 12 months from the date these consolidated financial statements were issued. The Company is subject to risks common to companies in the biotechnology industry, including, but not limited to, development by the Company or its competitors of technological innovations, risks of failure of clinical trials, dependence on key personnel, protection of proprietary technology, compliance with government regulations and ability to transition from clinical manufacturing to the commercial production of products.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation and Principles of Consolidation The accompanying consolidated financial statements are unaudited and have been prepared in conformity with accounting principles generally accepted in the United States of America (GAAP). The interim unaudited consolidated financial statements have been prepared on the same basis as the annual audited consolidated financial statements as of and for the year ended December 31, 2019 included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2019, which was filed with the SEC on February 26, 2020. Certain information and footnote disclosures required by GAAP which are normally included in the Company’s annual consolidated financial statements have been omitted pursuant to SEC rules and regulations for interim reporting. In the opinion of management, the accompanying consolidated financial statements reflect all adjustments, which are normal and recurring in nature, necessary for fair financial statement presentation. The results of operations for the interim periods are not necessarily indicative of the results of operations to be expected for the full year, any other interim periods, or any future year or period. These interim consolidated financial statements should be read in conjunction with the audited consolidated financial statements as of and for the year ended December 31, 2019, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2019. The accompanying consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts in the financial statements and accompanying notes. Actual results could differ materially from those estimates. Management considers many factors in selecting appropriate financial accounting policies and controls, and in developing the estimates and assumptions that are used in the preparation of these consolidated financial statements. Management must apply significant judgment in this process. In addition, other factors may affect estimates, including: expected business and operational changes, sensitivity and volatility associated with the assumptions used in developing estimates and whether historical trends are expected to be representative of future trends. The estimation process often may yield a range of potentially reasonable estimates of the ultimate future outcomes and management must select an amount that falls within that range of reasonable estimates. This process may result in actual results differing materially from those estimated amounts used in the preparation of the consolidated financial statements. Significant estimates are used in the following areas, among others: license and royalty revenue, the allowance for credit losses, stock-based compensation expense, accrued research and development expenses and other accrued liabilities, income taxes and the fair value of financial instruments. The Company is actively monitoring the impact of the COVID-19 pandemic on its business, results of operations and financial condition. The full extent to which the COVID-19 pandemic will directly or indirectly impact the Company’s business, results of operations and financial condition in the future is unknown at this time and will depend on future developments that are highly unpredictable. The most significant estimates affecting the Company’s consolidated financial statements that may be impacted by the COVID-19 pandemic are related to the Company’s assessment of credit losses on accounts receivable, contract assets and available-for-sale debt securities. Reclassifications Certain amounts reported in prior periods have been reclassified to conform to current period financial statement presentation. These reclassifications are not material and have no effect on previously reported financial position, results of operations and cash flows. Restricted Cash Restricted cash includes money market mutual funds used to collateralize irrevocable letters of credit as required by the Company’s lease agreements. The following table provides a reconciliation of cash and cash equivalents and restricted cash as reported on the consolidated balance sheets to the total of these amounts as reported at the end of the period in the consolidated statements of cash flows (in thousands): September 30, 2020 September 30, 2019 Cash and cash equivalents $ 93,220 $ 79,594 Restricted cash 1,330 1,053 Total cash and cash equivalents and restricted cash $ 94,550 $ 80,647 Accounts Receivable Accounts receivable primarily consist of consideration due to the Company resulting from its license agreements with NAV Technology Licensees. Accounts receivable include amounts invoiced to licensees as well as rights to consideration which have not yet been invoiced, including unbilled royalties, and for which payment is conditional solely upon the passage of time. If a licensee elects to terminate a license prior to the end of the license term, the licensed intellectual property is returned to the Company and any accounts receivable from the licensee which are not contractually payable to the Company are charged off as a reduction of license revenue in the period of the termination. Accounts receivable which are not expected to be received by the Company within 12 months from the reporting date are stated net of a discount to present value and recorded as non-current assets on the consolidated balance sheets. The present value discount is recognized as a reduction of revenue in the period in which the accounts receivable are initially recorded and is accreted as interest income from licensing over the term of the receivables. Accounts receivable are stated net of an allowance for credit losses, if deemed necessary based on the Company’s evaluation of collectability and potential credit losses. Management assesses the collectability of its accounts receivable using the specific identification of account balances, and considers the credit quality and financial condition of its significant customers, historical information regarding credit losses and the Company’s evaluation of current and expected future economic conditions. If necessary, an allowance for credit losses is recorded against accounts receivable such that the carrying value of accounts receivable reflects the net amount expected to be collected. Accounts receivable balances are written off against the allowance for credit losses when the potential for collectability is considered remote. Please refer to Note 7 for further information regarding the allowance for credit losses related to accounts receivable. Marketable Securities Marketable securities consist of available-for-sale debt securities and equity securities and are carried at fair value. Marketable debt securities with remaining maturity dates exceeding 12 months which are not intended to be sold prior to maturity for use in current operations are classified as non-current assets. Marketable equity securities are classified as current assets. Unrealized gains and losses on available-for-sale debt securities, net of any related tax effects, are excluded from results of operations and are included in other comprehensive income and reported as a separate component of stockholders’ equity until realized. The Company uses the aggregate portfolio approach to release the tax effects of unrealized gains and losses on available-for-sale debt securities in accumulated other comprehensive income . Purchase premiums and discounts on marketable debt securities are amortized or accreted into the cost basis over the life of the related security as adjustments to the yield using the effective-interest method. Interest income is recognized when earned. Unrealized gains and losses on marketable equity securities are included in results of operations as investment income . Realized gains and losses from the sale or maturity of marketable securities are based on the specific identification method and are included in results of operations as investment income . At each reporting date, the Company evaluates available-for-sale debt securities which have an amortized cost basis in excess of the fair value of the security to determine if the unrealized loss or any potential credit losses should be recognized in results of operations . If the Company does not have the intent and ability to hold the security until recovery of the unrealized loss, the difference between the fair value and amortized cost basis of the security is charged to results of operations resulting in a new amortized cost basis of the security. If the Company has the intent and ability to hold the security until recovery of the unrealized loss, the security is evaluated for potential credit losses. If a credit loss is deemed to exist, the credit loss is recognized in results of operations and an allowance for credit losses is recorded against the amortized cost basis of the security. In determining whether a credit loss exists related to impaired available-for-sale debt securities, the Company considers, among other factors, the extent of the unrealized loss relative to the amortized cost basis, the credit rating of the issuer and any recent changes thereto, current and expected future economic conditions, and any adverse events or other changes in circumstances that have occurred which may indicate a potential credit loss. The Company did not record an allowance for credit losses on its available-for-sale debt securities as of September 30, 2020. Fair Value of Financial Instruments The Company is required to disclose information on all assets and liabilities reported at fair value that enables an assessment of the inputs used in determining the reported fair values. Accounting Standards Codification (ASC) 820, Fair Value Measurements and Disclosures • Level 1—Valuations based on unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date. • Level 2—Valuations based on quoted prices for similar assets or liabilities in markets that are not active or for which all significant inputs are observable, either directly or indirectly. • Level 3—Valuations that require inputs that reflect the Company’s own assumptions that are both significant to the fair value measurement and unobservable. To the extent that valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. The fair values of the Company’s Level 2 instruments are based on quoted market prices or broker or dealer quotations for similar assets. These investments are initially valued at the transaction price and subsequently valued utilizing third party pricing providers or other market observable data. Please refer to Note 4 for further information on the fair value measurement of the Company’s financial instruments. Net Income (Loss) Per Share Basic net income (loss) per share is calculated by dividing net income (loss) applicable to common stockholders by the weighted-average common shares outstanding during the period, without consideration for common stock equivalents. Diluted net income (loss) per share is calculated by adjusting the weighted-average common shares outstanding for the dilutive effect of common stock equivalents outstanding for the period, determined using the treasury-stock method. Contingently convertible shares in which conversion is based on non-market-priced contingencies are excluded from the calculations of both basic and diluted net income (loss) per share until the contingency has been fully met. For purposes of the diluted net income (loss) per share calculation, common stock equivalents are excluded from the calculation of diluted net income (loss) per share if their effect would be anti-dilutive. Recent Accounting Pronouncements Recently Adopted Accounting Pronouncements In June 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement In August 2018, the FASB issued ASU 2018-15, Intangibles—Goodwill and Other—Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740)—Simplifying the Accounting for Income Taxes

Marketable Securities

Marketable Securities	9 Months Ended
	Sep. 30, 2020
Investments Debt And Equity Securities [Abstract]
Marketable Securities	3. Marketable Securities The following tables present a summary of the Company’s marketable securities, which consist of available-for-sale debt securities and equity securities (in thousands): Amortized Cost / Cost Unrealized Gains Unrealized Losses Fair Value September 30, 2020 U.S. government and federal agency securities $ 20,802 $ 77 $ — $ 20,879 Certificates of deposit 3,416 51 — 3,467 Corporate bonds 159,732 1,007 (11 ) 160,728 Equity securities 195 11,308 — 11,503 $ 184,145 $ 12,443 $ (11 ) $ 196,577 Amortized Cost / Cost Unrealized Gains Unrealized Losses Fair Value December 31, 2019 U.S. government and federal agency securities $ 62,637 $ 215 $ (5 ) $ 62,847 Certificates of deposit 8,506 77 — 8,583 Corporate bonds 226,137 808 (29 ) 226,916 Equity securities 351 31,784 — 32,135 $ 297,631 $ 32,884 $ (34 ) $ 330,481 As of September 30, 2020 and December 31, 2019, no available-for-sale debt securities had remaining maturities greater than three years. The amortized cost of marketable debt securities is adjusted for amortization of premiums and accretion of discounts to maturity, or to the earliest call date for callable debt securities purchased at a premium. As of September 30, 2020 and December 31, 2019, the balance in the Company’s accumulated other comprehensive income consisted solely of net unrealized gains and losses on available-for-sale debt securities, net of income tax effects and reclassification adjustments for realized gains and losses. During the three and nine months ended September 30, 2020, the Company recognized net unrealized gains (losses) on available-for-sale debt securities of $(0.5) million and $0.1 million, respectively, and income tax expense of zero in other comprehensive income (loss) for the period. The Company recognized net realized gains of less than $0.1 million and $0.1 million on the sale or maturity of available-for-sale debt securities during the three and nine months ended September 30, 2020, respectively, which were reclassified out of accumulated other comprehensive income during the period and were included in investment income (loss) in the consolidated statements of operations and comprehensive income (loss). During the three and nine months ended September 30, 2019, the Company recognized net unrealized gains (losses) on available-for-sale debt securities of $(0.1) million and $1.7 million, respectively, and income tax benefit (expense) of less than $0.1 million and $(0.6) million, respectively, in other comprehensive income (loss) for the period. The Company recognized net realized gains of less than $0.1 million on the sale or maturity of available-for-sale debt securities during the three and nine months ended September 30, 2019, which were reclassified out of accumulated other comprehensive income during the period and were included in investment income (loss) in the consolidated statements of operations and comprehensive income (loss). The following tables present the fair values and unrealized losses of available-for-sale debt securities held by the Company in an unrealized loss position for less than 12 months and 12 months or greater (in thousands): Less than 12 Months 12 Months or Greater Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses September 30, 2020 Corporate bonds $ 13,728 $ (11 ) $ — $ — $ 13,728 $ (11 ) $ 13,728 $ (11 ) $ — $ — $ 13,728 $ (11 ) Less than 12 Months 12 Months or Greater Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses December 31, 2019 U.S. government and federal agency securities $ 12,562 $ (5 ) $ — $ — $ 12,562 $ (5 ) Corporate bonds 48,556 (29 ) — — 48,556 (29 ) $ 61,118 $ (34 ) $ — $ — $ 61,118 $ (34 ) As of September 30, 2020, available-for-sale debt securities held by the Company which were in an unrealized loss position consisted of five investment grade security positions. The Company has the intent and ability to hold such securities until recovery, and due to the credit quality of the issuers and low severity of each unrealized loss position relative to its amortized cost basis, the Company did not identify any credit losses associated with its available-for-sale debt securities. The Company did not recognize any impairment or credit losses on available-for-sale debt securities during the three and nine months ended September 30, 2020. Marketable equity securities held by the Company as of September 30 , 2020 and December 31, 2019 consist ed solely of common stock of Prevail Therapeutics Inc. (Prevail). The Company acquired the securities as consideration for a commercial license to the NAV Technology Platform granted to Prevail in August 2017. Prevail completed its initial public offering (IPO) in June 2019. Prior to Prevail’s IPO, the securities were accounted for as non-marketable equity securities without a readily determinable fair value and had a carrying value of $ 0.4 million. Upon Prevail’s IPO in June 2019, the securities were reclassified to marketable securities and are measured at fair value. During the three and nine months ended September 30 , 2020, the Company recognized net realized and unrealized losses of $ 7.5 million and $ 8.3 million, respectively, related to its marketable equity securities of Prevail . During the three and nine months ended September 30, 2019, the Company recognized unrealized gains (losses) of $ (2.2) million and $ 29.4 million , respectively, and did no t recognize any realized gains or losses related to its marketable equity securities of Prevail.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	9 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	4. Fair Value of Financial Instruments Financial instruments reported at fair value on a recurring basis include cash equivalents and marketable securities. The following tables present the fair value of cash equivalents and marketable securities in accordance with the hierarchy discussed in Note 2 (in thousands): Quoted Significant prices other Significant in active observable unobservable markets inputs inputs (Level 1) (Level 2) (Level 3) Total September 30, 2020 Cash equivalents: Money market mutual funds $ — $ 70,805 $ — $ 70,805 Total cash equivalents — 70,805 — 70,805 Marketable securities: U.S. government and federal agency securities — 20,879 — 20,879 Certificates of deposit — 3,467 — 3,467 Corporate bonds — 160,728 — 160,728 Equity securities 11,503 — — 11,503 Total marketable securities 11,503 185,074 — 196,577 Total cash equivalents and marketable securities $ 11,503 $ 255,879 $ — $ 267,382 Quoted Significant prices other Significant in active observable unobservable markets inputs inputs (Level 1) (Level 2) (Level 3) Total December 31, 2019 Cash equivalents: Money market mutual funds $ — $ 56,058 $ — $ 56,058 Total cash equivalents — 56,058 — 56,058 Marketable securities: U.S. government and federal agency securities — 62,847 — 62,847 Certificates of deposit — 8,583 — 8,583 Corporate bonds — 226,916 — 226,916 Equity securities 32,135 — — 32,135 Total marketable securities 32,135 298,346 — 330,481 Total cash equivalents and marketable securities $ 32,135 $ 354,404 $ — $ 386,539 Management estimates that the carrying amounts of its current accounts receivable, accounts payable and accrued expenses and other current liabilities approximate fair value due to the short-term nature of those instruments. Accounts receivable which contain non-current portions are recorded at their present values using a discount rate that is based on prevailing market rates and the credit profile of the licensee on the date the amounts are initially recorded. Management does not believe there have been any significant changes in market conditions or credit quality that would cause the discount rates initially used to be significantly different from those that would be used as of September 30, 2020 to determine the present value of the receivables. Accordingly, management estimates that the carrying value of its non-current accounts receivable approximates the fair value of those instruments. Non-marketable equity securities are measured at cost less impairment, adjusted for observable price changes for identical or similar investments of the same issuer. As of September 30, 2020, non-marketable equity securities had a carrying value of $1.1 million and were included in other assets on the consolidated balance sheet. As of December 31, 2019, the Company did not hold any non-marketable equity securities. No remeasurements or impairment losses were recorded on non-marketable equity securities during the three and nine months ended September 30, 2020 and 2019.

Property and Equipment, Net

Property and Equipment, Net	9 Months Ended
	Sep. 30, 2020
Property Plant And Equipment [Abstract]
Property and Equipment, Net	5. Property and Equipment, Net Property and equipment, net consists of the following (in thousands): September 30, 2020 December 31, 2019 Laboratory and manufacturing equipment $ 23,162 $ 19,663 Computer equipment and software 3,272 2,545 Furniture and fixtures 2,898 2,188 Leasehold improvements 30,109 18,915 Total property and equipment 59,441 43,311 Accumulated depreciation and amortization (20,570 ) (14,338 ) Property and equipment, net $ 38,871 $ 28,973

Leases

Leases	9 Months Ended
	Sep. 30, 2020
Leases [Abstract]
Leases	6. Leases 9804 Medical Center Drive In November 2018, the Company entered into an operating lease, as amended in April 2019 and November 2019, for approximately 177,000 square feet of office, laboratory and manufacturing facilities in a new building to be constructed at 9804 Medical Center Drive in Rockville, Maryland (the 9804 Medical Center Drive Lease). The new facility will serve as the Company’s future corporate, research and manufacturing headquarters. The initial construction of the building was performed by the landlord, and the lease commenced in September 2020 upon the delivery of leased premises to the Company to make additional improvements to the building. Monthly payments under the lease begin in September 2021 and escalate annually in accordance with the lease agreement. The lease expires in September 2036 Pursuant to the 9804 Medical Center Drive Lease, the Company received a $19.5 million tenant improvement allowance from the landlord to perform improvements to the leased premises. The tenant improvement allowance has been recorded as a reduction of the right-of-use assets for the lease and is amortized on a straight-line basis as a reduction of lease expense over the term of the lease. As of September 30, 2020, the Company had unreimbursed amounts remaining under the tenant improvement allowance of $17.2 million, which were deemed in-substance lease payments and recorded as a reduction of the lease liability. As of September 30, 2020, the Company had recorded property and equipment of $17.3 million related to the buildout of the facility at 9804 Medical Center Drive, which have not yet been placed in service. The Company recorded the right-of-use assets and lease liabilities related to the 9804 Medical Center Drive Lease upon its commencement in September 2020. As of September 30, 2020, the Company had recorded right-of-use assets of $50.6 million and lease liabilities of $52.5 million related to the 9804 Medical Center Drive Lease. 9712 Medical Center Drive In March 2015, the Company entered into an operating lease for office space at 9712 Medical Center Drive in Rockville, Maryland (the 9712 Medical Center Drive Lease). The lease term commenced in April 2015. Monthly payments under the lease began in October 2015 and escalate annually in accordance with the lease agreement. In September 2015, November 2015, July 2017 and April 2018, the Company amended the 9712 Medical Center Drive Lease to include additional office and laboratory space at 9714 Medical Center Drive, and ultimately extend the term of the lease to September 2021. The Company had options to extend the term of the 9712 Medical Center Drive Lease for up to six additional years. Additionally, upon the commencement of the 9804 Medical Center Drive Lease in September 2020, the Company had the option to terminate the 9712 Medical Center Drive Lease with six months’ notice. The Company’s extension and termination options under the 9712 Medical Center Drive Lease were excluded from the measurement of the right-of-use assets and lease liabilities for the lease as they were not reasonably certain of exercise. The Company received a $0.4 million tenant improvement allowance from the landlord which has been recorded as a reduction of the right-of-use assets for the lease and is amortized on a straight-line basis as a reduction of lease expense over the term of the lease. In October 2020, the Company amended the 9712 Medical Center Drive Lease to extend the term of the lease to February 2027. Pursuant to the amendment, the Company has an option to extend the term of the lease for three additional years, as well as an option to extend the lease term to be coterminous with the 9804 Medical Center Drive Lease, which expires in September 2036. Total additional lease payments under the 9712 Medical Center Drive Lease as a result of the October 2020 amendment were $8.8 million, excluding any lease payments contingent upon the Company’s option to extend the term of the lease. 9600 Blackwell Road In January 2016, the Company entered into an operating lease for its corporate headquarters at 9600 Blackwell Road in Rockville, Maryland (the Blackwell Road Lease). The lease commenced in February 2016 and expires in September 2023 The Company had an option to extend the term of the Blackwell Road Lease for up to five additional years and the option to terminate the lease, with payment of an early termination fee, after 67 months from the lease commencement date. During the three months ended September 30, 2020, the Company reassessed the term of the Blackwell Road Lease and determined that as of September 30, 2020, it was reasonably certain that the Company will exercise its termination option under the lease. Accordingly, the measurement of the right-of-use assets and lease liabilities for the Blackwell Road Lease were reduced by $0.7 million during the three months ended September 30, 2020, to reflect the payment of the early termination fee and the revised lease term through September 2021. In November 2020, the Company exercised its termination option under the Blackwell Road Lease. As a result of the termination, the lease will expire in September 2021 400 Madison Avenue In May 2016, the Company entered into an operating lease for office space at 400 Madison Avenue in New York, New York (the 400 Madison Lease). The lease commenced in July 2016 and monthly payments under the lease began in October 2016 and escalate annually in accordance with the lease agreement. In May 2019, the 400 Madison Lease was amended to include additional office space and extend the term of the lease from October 2020 to April 2027. The Company received a $0.7 million tenant improvement allowance from the landlord which has been recorded as a reduction of the right-of-use assets for the lease and is amortized on a straight-line basis as a reduction of lease expense over the term of the lease. As required by the lease agreement, the Company has provided the landlord with an irrevocable letter of credit of $0.2 million which the landlord may draw upon in the event of any uncured default by the Company under the terms of the lease. Other Leases The Company leases additional office and laboratory facilities, laboratory equipment and other equipment under operating leases with various expiration dates through 2028, including leases which have been executed but have not yet commenced. Operating Lease Information All of the Company’s leases are classified as operating leases. The following table summarizes the Company’s lease costs and supplemental cash flow information related to its operating leases (in thousands): Three Months Ended Nine Months Ended September 30, 2020 September 30, 2020 Operating lease cost $ 997 $ 2,793 Variable lease cost 174 575 Total lease cost $ 1,171 $ 3,368 Cash paid for amounts included in operating lease liabilities $ 988 $ 2,482 Right-of-use assets acquired through operating lease liabilities $ 49,734 $ 49,734 Right-of-use assets acquired through operating lease liabilities for the three and nine months ended September 30, 2020 include a reduction of $0.7 million related to the Company’s change in estimate regarding the exercise of its termination rights under the Blackwell Road Lease. Short-term lease expense for the three and nine months ended September 30, 2020 was not material and is included in operating lease cost in the table above. Variable lease cost under the Company’s operating leases includes items such as common area maintenance, utilities, taxes and other charges. The weighted-average remaining lease term and weighted-average discount rate of the Company’s operating leases were as follows: As of September 30, 2020 Weighted-average remaining lease term (years) 13.8 Weighted-average discount rate 5.4 % The following table presents a reconciliation of the undiscounted future minimum lease payments remaining the Company’s operating leases to the amounts reported as operating lease liabilities on the consolidated balance sheet as of September 30, 2020 (in thousands): As of September 30, 2020 Undiscounted future minimum lease payments: 2020 (remainder of year) $ 1,117 2021 3,964 2022 5,055 2023 6,980 2024 8,000 Thereafter 99,184 Total undiscounted future minimum lease payments $ 124,300 Amount representing imputed interest (45,843 ) Tenant improvement allowance not yet received (17,432 ) Total operating lease liabilities 61,025 Current portion of operating lease liabilities (3,564 ) Operating lease liabilities, non-current $ 57,461 The table above excludes future minimum lease payments for leases which were executed but had not yet commenced as of September 30, 2020, the total of which were not material.

License and Royalty Revenue

License and Royalty Revenue	9 Months Ended
	Sep. 30, 2020
License Agreement Revenue Recognition [Abstract]
License and Royalty Revenue	7. License and Royalty Revenue As of September 30, 2020, the Company’s NAV Technology Platform was being applied by NAV Technology Licensees in one commercial product, Zolgensma, and in the development of more than 20 product candidates. Consideration to the Company under its license agreements may include: (i) up-front and annual fees, (ii) option fees to acquire additional licenses, (iii) milestone payments based on the achievement of certain development and sales-based milestones by licensees, (iv) sublicense fees and (v) royalties on sales of licensed products. Sublicense fees vary by license and range from a mid-single digit percentage to a low-double digit percentage of license fees received by licensees as a result of sublicenses. Royalties on net sales of commercialized products vary by license and range from a mid-single digit percentage to a low double-digit percentage of net sales by licensees. Development milestone payments are evaluated each reporting period and are only included in the transaction price of each license and recognized as license revenue to the extent the milestones are considered probable of achievement. Sales-based milestones are excluded from the transaction price of each license agreement and recognized as royalty revenue in the period of achievement. As of September 30, 2020, the Company’s license agreements, excluding additional licenses that could be granted upon the exercise of options by licensees, contained unachieved milestones which could result in aggregate milestone payments to the Company of up to $213.4 million, including (i) $0.3 million upon the submission of preclinical regulatory filings, (ii) $26.6 million upon the commencement of various stages of clinical trials, (iii) $26.0 million upon the submission of regulatory approval filings, (iv) $103.5 million upon the approval of commercial products by regulatory agencies and (v) $57.0 million upon the achievement of specified sales targets for licensed products. To the extent the milestone payments are realized by the Company, the Company will be obligated to pay sublicense fees to licensors based on a specified percentage of the fees earned by the Company. The achievement of milestones by licensees is highly dependent on the successful development and commercialization of licensed products and it is at least reasonably possible that some or all of the milestone fees will not be realized by the Company. Accounts Receivable, Contract Assets and Deferred Revenue The following table presents changes in the balances of the Company’s receivables, contract assets and deferred revenue, as well as other information regarding revenue recognized during the periods presented (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Accounts receivable, current and non-current: Balance, beginning of period $ 46,494 $ 33,634 $ 42,303 $ 31,599 Additions 100,243 15,526 137,220 26,575 Deductions (21,057 ) (5,640 ) (53,843 ) (14,654 ) Balance, end of period $ 125,680 $ 43,520 $ 125,680 $ 43,520 Contract assets: Balance, beginning of period $ 350 $ — $ — $ 750 Additions — — 350 1,000 Deductions — — — (1,750 ) Balance, end of period $ 350 $ — $ 350 $ — Deferred revenue, current and non-current: Balance, beginning of period $ 4,457 $ 3,333 $ 3,333 $ 3,933 Additions — — 1,124 — Deductions (113 ) — (113 ) (600 ) Balance, end of period $ 4,344 $ 3,333 $ 4,344 $ 3,333 Revenue recognized during the period from: Amounts included in deferred revenue at beginning of period $ 113 $ — $ — $ 600 Performance obligations satisfied in previous periods $ 98,799 $ 10,072 $ 125,555 $ 15,037 Additions to accounts receivable during the periods presented consisted primarily of royalties on net sales of Zolgenmsa, billed and unbilled receivables recorded for the achievement of milestones by licensees during the period, receivables recorded related to new licenses granted by the Company, and interest income recognized related to significant financing components. Deductions to accounts receivable during the periods presented primarily consisted of amounts collected from licensees and increases in the allowance for credit losses. Additions to contract assets during the periods presented consisted of development milestones deemed probable of achievement by licensees during the periods. Deductions to contract assets during the periods presented consisted of the achievement of such milestones and billing of the associated milestone payments by the Company. Accounts receivable, net consisted of the following (in thousands): September 30, 2020 December 31, 2019 Current accounts receivable: Billed to customers $ 30,086 $ 376 Unbilled 99,708 37,772 Allowance for credit losses (7,678 ) — Current accounts receivable, net 122,116 38,148 Non-current accounts receivable: Unbilled 3,564 4,155 Allowance for credit losses — — Non-current accounts receivable, net 3,564 4,155 Total accounts receivable, net $ 125,680 $ 42,303 The following table presents the changes in the allowance for credit losses related to accounts receivable and contract assets for the nine months ended September 30, 2020 (in thousands): Accounts Receivable Contract Assets Balance at December 31, 2019 $ — $ — Provision for credit losses 7,678 — Write-offs — — Balance at September 30, 2020 $ 7,678 $ — The Company’s allowance for credit losses as of September 30, 2020 was related solely to accounts receivable from Abeona Therapeutics Inc. (Abeona). Please refer to the section below, Abeona Therapeutics Inc., for further information regarding amounts due from Abeona and the associated allowance for credit losses. The Company’s provision for credit losses for the three and nine months ended September 30, 2020 was $7.7 million and was related solely to changes in estimates regarding the allowance for credit losses associated with the accounts receivable from Abeona. No provision for credit losses was recorded for the three or nine months ended September 30, 2019. As of September 30, 2020, the Company had recorded deferred revenue of $4.3 million which represents consideration received from licensees for performance obligations that have not yet been satisfied by the Company. Unsatisfied performance obligations consist of (i) options granted to licensees that provide material rights to the licensee to acquire additional licenses from the Company, which will be satisfied upon the exercise or expiration of the options and (ii) research and development services to be performed by the Company related to licensed products, which will be satisfied as the research and development services are performed. Revenue recognized from performance obligations satisfied in previous periods was primarily attributable to royalty and sublicense revenues as well as changes in transaction prices of the Company’s license agreements during the periods. Changes in transaction prices were primarily attributable to development milestones achieved or deemed probable of achievement during the periods, which were previously not considered probable of achievement. AveXis March 2014 License In March 2014, the Company entered into an exclusive license agreement, as amended in January 2018 (the March 2014 License) with AveXis, Inc. (AveXis). Under the March 2014 License, the Company granted AveXis an exclusive, worldwide commercial license, with rights to sublicense, to the NAV Technology Platform, as well as other certain rights, for the treatment of spinal muscular atrophy (SMA) in humans by in vivo gene therapy. AveXis launched commercial sales of Zolgensma, a licensed product under the March 2014 License, in the second quarter of 2019, upon which the Company began recognizing royalty revenue on net sales of the licensed product. Pursuant to the March 2014 License, AveXis was obligated to pay a sales-based milestone fee of $80.0 million to the Company upon the achievement of $1.0 billion in cumulative net sales of licensed products. AveXis achieved cumulative net sales of Zolgensma of $1.0 billion in third quarter of 2020, upon which the Company recognized revenue of $80.0 million related to the sales-based milestone fee. The $80.0 milestone fee was recorded as accounts receivable as of September 30, 2020, and the Company received payment of the $80.0 million milestone fee from AveXis in October 2020. The Company recognized the following amounts under the March 2014 License with AveXis (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 License revenue $ — $ — $ 3,500 $ 3,500 Royalties on net sales of Zolgensma 18,799 9,182 40,723 10,106 Achievement of sales-based milestone for Zolgensma 80,000 — 80,000 — Total license and royalty revenue $ 98,799 $ 9,182 $ 124,223 $ 13,606 Interest income from licensing $ 6 $ 7 $ 20 $ 22 As of September 30, 2020, the Company had recorded total accounts receivable of $98.9 million from AveXis under the March 2014 License, of which $98.8 million were included in current assets and $0.1 million were included in non-current assets. As of December 31, 2019, the Company had recorded total accounts receivable of $11.0 million from AveXis under the March 2014 License, of which $10.8 million were included in current assets and $0.2 million were included in non-current assets. Abeona Therapeutics Inc. In November 2018, the Company entered into a license agreement with Abeona, as amended in November 2019 (the November 2018 License), for the development and commercialization of various diseases using the NAV Technology Platform. Pursuant to the November 2018 License, Abeona was required to pay a license fee of $8.0 million to the Company no later than April 1, 2020. Abeona failed to make this payment, and in April 2020, the Company delivered to Abeona a notice of its breach of the license agreement and written demand for payment. Upon expiration of the applicable cure period in May 2020, the license agreement was terminated. As a result of the termination, Abeona was required to pay a $20.0 million license fee to the Company within 15 days of the termination date, which otherwise would have been due to the Company in November 2020. As of October 30, 2020, the Company had not received any portion of the $28.0 million in license fees due from Abeona under the license agreement. Unpaid balances due under the November 2018 License accrue interest at 1.5% per month. During the three and nine months ended September 30, 2020, the Company recognized interest income from licensing of $1.3 million and $2.1 million, respectively, related to the unpaid license fees from Abeona under the November 2018 License. Total accounts receivable from Abeona recorded as of September 30, 2020 was $30.1 million, consisting of the unpaid license fees and associated accrued interest. In May 2020, subsequent to the termination of the November 2018 License, Abeona filed a claim in arbitration alleging that the Company had breached certain responsibilities to communicate with Abeona regarding the Company’s prosecution of licensed patents under the November 2018 License. The Company disputes Abeona’s claim and has filed a counterclaim in arbitration demanding payment of the $28.0 million of unpaid fees from Abeona, plus accrued interest. Based on its evaluation of the merits of Abeona’s claims, the Company had not recorded any liabilities related these claims as of September 30, 2020, and the Company currently expects that its demand for payment in full will be upheld in arbitration. The Company intends to enforce the full collection of all amounts due from Abeona upon completion of arbitration, which is currently scheduled to occur in March 2021. However, the duration and outcome of arbitration and timing of payment from Abeona are unpredictable and uncertain at this time. While the Company currently expects its demand for payment in full will be upheld in arbitration, the Company assessed the collectability of the $30.1 million due from Abeona as of September 30, 2020 as it relates to credit risk. In performing this assessment, the Company evaluated Abeona’s credit profile and financial condition, as well its expectations regarding Abeona’s future cash flows and ability to satisfy this obligation upon the completion of arbitration in 2021. Additionally, the Company considered Abeona’s continued failure to remit payment to the Company, as well as events which occurred during the three months ended September 30, 2020 impacting Abeona’s business and credit profile, specifically the departure of key members of Abeona’s management and board of directors and subsequent decline in market capitalization. As a result of this analysis, the Company recorded an allowance for credit losses of $7.7 million as of September 30, 2020 related to the accounts receivable due from Abeona. However, management intends to enforce the full collection of all amounts due from Abeona upon the completion of arbitration. In accordance with the Company’s interest accrual policy, the Company will cease the recognition of interest income accrued under the license agreement subsequent to the recognition of the allowance for credit losses unless and until such amounts are deemed to be collectable.

Stock-based Compensation

Stock-based Compensation	9 Months Ended
	Sep. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-based Compensation	8. Stock-based Compensation In January 2020, the Board of Directors authorized an additional 1,479,696 shares to be issued under the 2015 Equity Incentive Plan (the 2015 Plan). As of September 30, 2020, the total number of shares of common stock authorized for issuance under the 2015 Plan and the 2014 Stock Plan (the 2014 Plan) was 12,412,917, of which 2,321,306 remained available for future grants under the 2015 Plan. Stock-based Compensation Expense The Company’s stock-based compensation expense by award type was as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Stock options $ 7,880 $ 6,965 $ 23,745 $ 19,261 Restricted stock units — 69 — 206 Employee stock purchase plan 155 128 623 512 $ 8,035 $ 7,162 $ 24,368 $ 19,979 As of September 30, 2020, the Company had $68.6 million of unrecognized stock-based compensation expense related to stock options and the 2015 Employee Stock Purchase Plan (the 2015 ESPP), which is expected to be recognized over a weighted-average period of 2.5 years. The Company has recorded aggregate stock-based compensation expense in the consolidated statements of operations and comprehensive income (loss) as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Research and development $ 4,110 $ 3,657 $ 12,442 $ 9,530 General and administrative 3,925 3,505 11,926 10,449 $ 8,035 $ 7,162 $ 24,368 $ 19,979 Stock Options The following table summarizes stock option activity under the 2014 Plan and 2015 Plan (in thousands, except per share data): Weighted- average Weighted- Remaining average Contractual Aggregate Exercise Life Intrinsic Shares Price (Years) Value (a) Outstanding at December 31, 2019 5,544 $ 28.79 7.5 $ 86,509 Granted 1,542 $ 38.25 Exercised (356 ) $ 11.92 Cancelled or forfeited (321 ) $ 45.11 Outstanding at September 30, 2020 6,409 $ 31.18 7.4 $ 37,396 Exercisable at September 30, 2020 3,581 $ 23.34 6.3 $ 36,885 Vested and expected to vest at September 30, 2020 6,409 $ 31.18 7.4 $ 37,396 (a) The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying options and the fair value of the common stock for the options that were in the money at the dates reported. The weighted-average grant date fair value per share of options granted during the nine months ended September 30, 2020 was $24.08. During the nine months ended September 30, 2020, the total number of stock options exercised was 356,302, resulting in total proceeds of $4.2 million. The total intrinsic value of options exercised during the nine months ended September 30, 2020 was $9.4 million. Employee Stock Purchase Plan In January 2020, the Board of Directors authorized an additional 369,924 shares to be issued under the 2015 ESPP. As of September 30, 2020, the total number of shares of common stock authorized for issuance under the 2015 ESPP was 623,924, of which 448,011 remained available for future issuance. During the nine months ended September 30, 2020, 55,499 shares of common stock were issued under the 2015 ESPP.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Income Taxes	9. Income Taxes The Company has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets. Based on the Company’s history of operating losses, including three-year cumulative loss positions as of September 30, 2020 and December 31, 2019, the Company concluded that it is more likely than not that the benefit of its deferred tax assets will not be realized. Accordingly, the Company provided a full valuation allowance for its net deferred tax assets as of September 30, 2020 and December 31, 2019. In response to the COVID-19 pandemic, the Coronavirus Aid, Relief and Economic Security Act (the CARES Act) was signed into law in March 2020. The CARES Act (i) lifts certain deduction limitations originally imposed by the Tax Cuts and Jobs Act of 2017 (the TCJA), (ii) allows corporate taxpayers to carryback net operating losses (NOLs) originating during 2018 through 2020 for up to five years, which was not previously allowed under the TCJA, (iii) eliminates the 80% of taxable income limitations on NOL utilization imposed by the TCJA, allowing corporate entities to fully utilize NOL carryforwards to offset taxable income in 2018, 2019 or 2020, and (iv) enacts various other changes to corporate taxation. Also included in the CARES Act was a change to the TCJA related to qualified improvement property, retroactively allowing for a 15-year recovery period and bonus depreciation. As a result of this change, the Company recorded current income tax benefit of $0.5 million during the nine months ended September 30, 2020 related to a reduction of state taxes associated with additional depreciation deductions allowed for the 2018 tax year. Overall, the enactment of the CARES Act, including the change for qualified improvement property, did not result in any material adjustments to the Company’s income tax provision for the three and nine months ended September 30, 2020, or to the Company’s net deferred tax assets as of September 30, 2020.

Related Party Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 2020
Related Party Transactions [Abstract]
Related Party Transactions	10. Related Party Transactions FOXKISER LLP Since 2016, the Company has been party to professional services agreements with FOXKISER LLP (FOXKISER), an affiliate of certain stockholders of the Company and an affiliate of a member of the Company’s Board of Directors, pursuant to which the Company pays a fixed monthly fee in consideration for certain strategic services provided by FOXKISER. Effective January 2019, the Company entered into a new professional services agreement with FOXKISER with similar terms and conditions as the previous agreements. The agreement was amended effective June 2019 to expand the scope of services provided and increase the monthly fee. Effective August 2020, the agreement was further amended to extend the term of the agreement by two years through December 2022. The agreement may be terminated by either party with six months’ advance written notice. Expenses incurred under the agreements with FOXKISER for the three and nine months ended September 30, 2020 were $1.2 million and $3.6 million, respectively. Expenses incurred under the agreements with FOXKISER for the three and nine months ended September 30, 2019 were $1.2 million and $2.9 million, respectively. Expenses incurred under the agreements with FOXKISER were recorded as research and development expenses in the consolidated statements of operations and comprehensive income (loss).

Net Loss Per Share

Net Loss Per Share	9 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Net Loss Per Share	11. Net Income (Loss) Per Share The computations of basic and diluted net income (loss) per share were as follows (in thousands, except per share data): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Basic net income (loss) per share: Net income (loss) $ 8,791 $ (34,584 ) $ (65,009 ) $ (68,269 ) Shares used in computation: Weighted-average common shares outstanding 37,342 36,813 37,234 36,618 Basic net income (loss) per share $ 0.24 $ (0.94 ) $ (1.75 ) $ (1.86 ) Diluted net income (loss) per share: Net income (loss) $ 8,791 $ (34,584 ) $ (65,009 ) $ (68,269 ) Shares used in computation: Weighted-average common shares outstanding 37,342 36,813 37,234 36,618 Stock options 1,529 — — — Employee stock purchase plan 6 — — — Weighted-average diluted common shares 38,877 36,813 37,234 36,618 Diluted net income (loss) per share $ 0.23 $ (0.94 ) $ (1.75 ) $ (1.86 ) For periods in which the Company incurred net losses, common stock equivalents were excluded from the calculation of diluted net loss per share as their effect would be anti-dilutive. Accordingly, basic and diluted net loss per share were the same for such periods. The following potentially dilutive common stock equivalents outstanding at the end of the period were excluded from the computations of weighted-average diluted common shares for the periods indicated as their effects would be anti-dilutive (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Stock options issued and outstanding 4,072 5,530 6,409 5,530 Unvested restricted stock units outstanding — 40 — 40 Employee stock purchase plan — 16 21 16 4,072 5,586 6,430 5,586

Supplemental Disclosures

Supplemental Disclosures	9 Months Ended
	Sep. 30, 2020
Payables And Accruals [Abstract]
Supplemental Disclosures	12. Supplemental Disclosures Accrued expenses and other current liabilities consisted of the following (in thousands): September 30, 2020 December 31, 2019 Accrued sublicense fees and royalties $ 19,285 $ 4,542 Accrued personnel costs 10,380 10,903 Accrued external research and development expenses 9,163 5,791 Accrued external general and administrative expenses 2,873 2,053 Accrued purchases of property and equipment 2,438 1,328 Other accrued expenses and current liabilities 217 229 $ 44,356 $ 24,846

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Basis of Presentation and Principles of Consolidation	Basis of Presentation and Principles of Consolidation The accompanying consolidated financial statements are unaudited and have been prepared in conformity with accounting principles generally accepted in the United States of America (GAAP). The interim unaudited consolidated financial statements have been prepared on the same basis as the annual audited consolidated financial statements as of and for the year ended December 31, 2019 included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2019, which was filed with the SEC on February 26, 2020. Certain information and footnote disclosures required by GAAP which are normally included in the Company’s annual consolidated financial statements have been omitted pursuant to SEC rules and regulations for interim reporting. In the opinion of management, the accompanying consolidated financial statements reflect all adjustments, which are normal and recurring in nature, necessary for fair financial statement presentation. The results of operations for the interim periods are not necessarily indicative of the results of operations to be expected for the full year, any other interim periods, or any future year or period. These interim consolidated financial statements should be read in conjunction with the audited consolidated financial statements as of and for the year ended December 31, 2019, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2019. The accompanying consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts in the financial statements and accompanying notes. Actual results could differ materially from those estimates. Management considers many factors in selecting appropriate financial accounting policies and controls, and in developing the estimates and assumptions that are used in the preparation of these consolidated financial statements. Management must apply significant judgment in this process. In addition, other factors may affect estimates, including: expected business and operational changes, sensitivity and volatility associated with the assumptions used in developing estimates and whether historical trends are expected to be representative of future trends. The estimation process often may yield a range of potentially reasonable estimates of the ultimate future outcomes and management must select an amount that falls within that range of reasonable estimates. This process may result in actual results differing materially from those estimated amounts used in the preparation of the consolidated financial statements. Significant estimates are used in the following areas, among others: license and royalty revenue, the allowance for credit losses, stock-based compensation expense, accrued research and development expenses and other accrued liabilities, income taxes and the fair value of financial instruments. The Company is actively monitoring the impact of the COVID-19 pandemic on its business, results of operations and financial condition. The full extent to which the COVID-19 pandemic will directly or indirectly impact the Company’s business, results of operations and financial condition in the future is unknown at this time and will depend on future developments that are highly unpredictable. The most significant estimates affecting the Company’s consolidated financial statements that may be impacted by the COVID-19 pandemic are related to the Company’s assessment of credit losses on accounts receivable, contract assets and available-for-sale debt securities.
Reclassifications	Reclassifications Certain amounts reported in prior periods have been reclassified to conform to current period financial statement presentation. These reclassifications are not material and have no effect on previously reported financial position, results of operations and cash flows.
Restricted Cash	Restricted Cash Restricted cash includes money market mutual funds used to collateralize irrevocable letters of credit as required by the Company’s lease agreements. The following table provides a reconciliation of cash and cash equivalents and restricted cash as reported on the consolidated balance sheets to the total of these amounts as reported at the end of the period in the consolidated statements of cash flows (in thousands): September 30, 2020 September 30, 2019 Cash and cash equivalents $ 93,220 $ 79,594 Restricted cash 1,330 1,053 Total cash and cash equivalents and restricted cash $ 94,550 $ 80,647
Accounts Receivable	Accounts Receivable Accounts receivable primarily consist of consideration due to the Company resulting from its license agreements with NAV Technology Licensees. Accounts receivable include amounts invoiced to licensees as well as rights to consideration which have not yet been invoiced, including unbilled royalties, and for which payment is conditional solely upon the passage of time. If a licensee elects to terminate a license prior to the end of the license term, the licensed intellectual property is returned to the Company and any accounts receivable from the licensee which are not contractually payable to the Company are charged off as a reduction of license revenue in the period of the termination. Accounts receivable which are not expected to be received by the Company within 12 months from the reporting date are stated net of a discount to present value and recorded as non-current assets on the consolidated balance sheets. The present value discount is recognized as a reduction of revenue in the period in which the accounts receivable are initially recorded and is accreted as interest income from licensing over the term of the receivables. Accounts receivable are stated net of an allowance for credit losses, if deemed necessary based on the Company’s evaluation of collectability and potential credit losses. Management assesses the collectability of its accounts receivable using the specific identification of account balances, and considers the credit quality and financial condition of its significant customers, historical information regarding credit losses and the Company’s evaluation of current and expected future economic conditions. If necessary, an allowance for credit losses is recorded against accounts receivable such that the carrying value of accounts receivable reflects the net amount expected to be collected. Accounts receivable balances are written off against the allowance for credit losses when the potential for collectability is considered remote. Please refer to Note 7 for further information regarding the allowance for credit losses related to accounts receivable.
Marketable Securities	Marketable Securities Marketable securities consist of available-for-sale debt securities and equity securities and are carried at fair value. Marketable debt securities with remaining maturity dates exceeding 12 months which are not intended to be sold prior to maturity for use in current operations are classified as non-current assets. Marketable equity securities are classified as current assets. Unrealized gains and losses on available-for-sale debt securities, net of any related tax effects, are excluded from results of operations and are included in other comprehensive income and reported as a separate component of stockholders’ equity until realized. The Company uses the aggregate portfolio approach to release the tax effects of unrealized gains and losses on available-for-sale debt securities in accumulated other comprehensive income . Purchase premiums and discounts on marketable debt securities are amortized or accreted into the cost basis over the life of the related security as adjustments to the yield using the effective-interest method. Interest income is recognized when earned. Unrealized gains and losses on marketable equity securities are included in results of operations as investment income . Realized gains and losses from the sale or maturity of marketable securities are based on the specific identification method and are included in results of operations as investment income . At each reporting date, the Company evaluates available-for-sale debt securities which have an amortized cost basis in excess of the fair value of the security to determine if the unrealized loss or any potential credit losses should be recognized in results of operations . If the Company does not have the intent and ability to hold the security until recovery of the unrealized loss, the difference between the fair value and amortized cost basis of the security is charged to results of operations resulting in a new amortized cost basis of the security. If the Company has the intent and ability to hold the security until recovery of the unrealized loss, the security is evaluated for potential credit losses. If a credit loss is deemed to exist, the credit loss is recognized in results of operations and an allowance for credit losses is recorded against the amortized cost basis of the security. In determining whether a credit loss exists related to impaired available-for-sale debt securities, the Company considers, among other factors, the extent of the unrealized loss relative to the amortized cost basis, the credit rating of the issuer and any recent changes thereto, current and expected future economic conditions, and any adverse events or other changes in circumstances that have occurred which may indicate a potential credit loss. The Company did not record an allowance for credit losses on its available-for-sale debt securities as of September 30, 2020.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company is required to disclose information on all assets and liabilities reported at fair value that enables an assessment of the inputs used in determining the reported fair values. Accounting Standards Codification (ASC) 820, Fair Value Measurements and Disclosures • Level 1—Valuations based on unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date. • Level 2—Valuations based on quoted prices for similar assets or liabilities in markets that are not active or for which all significant inputs are observable, either directly or indirectly. • Level 3—Valuations that require inputs that reflect the Company’s own assumptions that are both significant to the fair value measurement and unobservable. To the extent that valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. The fair values of the Company’s Level 2 instruments are based on quoted market prices or broker or dealer quotations for similar assets. These investments are initially valued at the transaction price and subsequently valued utilizing third party pricing providers or other market observable data. Please refer to Note 4 for further information on the fair value measurement of the Company’s financial instruments.
Net Income (Loss) Per Share	Net Income (Loss) Per Share Basic net income (loss) per share is calculated by dividing net income (loss) applicable to common stockholders by the weighted-average common shares outstanding during the period, without consideration for common stock equivalents. Diluted net income (loss) per share is calculated by adjusting the weighted-average common shares outstanding for the dilutive effect of common stock equivalents outstanding for the period, determined using the treasury-stock method. Contingently convertible shares in which conversion is based on non-market-priced contingencies are excluded from the calculations of both basic and diluted net income (loss) per share until the contingency has been fully met. For purposes of the diluted net income (loss) per share calculation, common stock equivalents are excluded from the calculation of diluted net income (loss) per share if their effect would be anti-dilutive.
Recent Accounting Pronouncements	Recent Accounting Pronouncements Recently Adopted Accounting Pronouncements In June 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement In August 2018, the FASB issued ASU 2018-15, Intangibles—Goodwill and Other—Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740)—Simplifying the Accounting for Income Taxes

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Summary of Reconciliation of Cash and Cash Equivalents and Restricted Cash	The following table provides a reconciliation of cash and cash equivalents and restricted cash as reported on the consolidated balance sheets to the total of these amounts as reported at the end of the period in the consolidated statements of cash flows (in thousands): September 30, 2020 September 30, 2019 Cash and cash equivalents $ 93,220 $ 79,594 Restricted cash 1,330 1,053 Total cash and cash equivalents and restricted cash $ 94,550 $ 80,647

Marketable Securities (Tables)

Marketable Securities (Tables)	9 Months Ended
	Sep. 30, 2020
Investments Debt And Equity Securities [Abstract]
Summary of Company Marketable Securities	The following tables present a summary of the Company’s marketable securities, which consist of available-for-sale debt securities and equity securities (in thousands): Amortized Cost / Cost Unrealized Gains Unrealized Losses Fair Value September 30, 2020 U.S. government and federal agency securities $ 20,802 $ 77 $ — $ 20,879 Certificates of deposit 3,416 51 — 3,467 Corporate bonds 159,732 1,007 (11 ) 160,728 Equity securities 195 11,308 — 11,503 $ 184,145 $ 12,443 $ (11 ) $ 196,577 Amortized Cost / Cost Unrealized Gains Unrealized Losses Fair Value December 31, 2019 U.S. government and federal agency securities $ 62,637 $ 215 $ (5 ) $ 62,847 Certificates of deposit 8,506 77 — 8,583 Corporate bonds 226,137 808 (29 ) 226,916 Equity securities 351 31,784 — 32,135 $ 297,631 $ 32,884 $ (34 ) $ 330,481
Summary of Fair Values and Unrealized Losses of Marketable Securities Held by the Company in an Unrealized Loss Position for Less Than 12 months and 12 Months or Greater	The following tables present the fair values and unrealized losses of available-for-sale debt securities held by the Company in an unrealized loss position for less than 12 months and 12 months or greater (in thousands): Less than 12 Months 12 Months or Greater Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses September 30, 2020 Corporate bonds $ 13,728 $ (11 ) $ — $ — $ 13,728 $ (11 ) $ 13,728 $ (11 ) $ — $ — $ 13,728 $ (11 ) Less than 12 Months 12 Months or Greater Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses December 31, 2019 U.S. government and federal agency securities $ 12,562 $ (5 ) $ — $ — $ 12,562 $ (5 ) Corporate bonds 48,556 (29 ) — — 48,556 (29 ) $ 61,118 $ (34 ) $ — $ — $ 61,118 $ (34 )

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Schedule of Fair Value of Cash Equivalents and Marketable Securities	The following tables present the fair value of cash equivalents and marketable securities in accordance with the hierarchy discussed in Note 2 (in thousands): Quoted Significant prices other Significant in active observable unobservable markets inputs inputs (Level 1) (Level 2) (Level 3) Total September 30, 2020 Cash equivalents: Money market mutual funds $ — $ 70,805 $ — $ 70,805 Total cash equivalents — 70,805 — 70,805 Marketable securities: U.S. government and federal agency securities — 20,879 — 20,879 Certificates of deposit — 3,467 — 3,467 Corporate bonds — 160,728 — 160,728 Equity securities 11,503 — — 11,503 Total marketable securities 11,503 185,074 — 196,577 Total cash equivalents and marketable securities $ 11,503 $ 255,879 $ — $ 267,382 Quoted Significant prices other Significant in active observable unobservable markets inputs inputs (Level 1) (Level 2) (Level 3) Total December 31, 2019 Cash equivalents: Money market mutual funds $ — $ 56,058 $ — $ 56,058 Total cash equivalents — 56,058 — 56,058 Marketable securities: U.S. government and federal agency securities — 62,847 — 62,847 Certificates of deposit — 8,583 — 8,583 Corporate bonds — 226,916 — 226,916 Equity securities 32,135 — — 32,135 Total marketable securities 32,135 298,346 — 330,481 Total cash equivalents and marketable securities $ 32,135 $ 354,404 $ — $ 386,539

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	9 Months Ended
	Sep. 30, 2020
Property Plant And Equipment [Abstract]
Schedule of Property and Equipment	Property and equipment, net consists of the following (in thousands): September 30, 2020 December 31, 2019 Laboratory and manufacturing equipment $ 23,162 $ 19,663 Computer equipment and software 3,272 2,545 Furniture and fixtures 2,898 2,188 Leasehold improvements 30,109 18,915 Total property and equipment 59,441 43,311 Accumulated depreciation and amortization (20,570 ) (14,338 ) Property and equipment, net $ 38,871 $ 28,973

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2020
Leases [Abstract]
Summary of Lease Costs and Supplemental Cash Flow Information of Operating Leases	All of the Company’s leases are classified as operating leases. The following table summarizes the Company’s lease costs and supplemental cash flow information related to its operating leases (in thousands): Three Months Ended Nine Months Ended September 30, 2020 September 30, 2020 Operating lease cost $ 997 $ 2,793 Variable lease cost 174 575 Total lease cost $ 1,171 $ 3,368 Cash paid for amounts included in operating lease liabilities $ 988 $ 2,482 Right-of-use assets acquired through operating lease liabilities $ 49,734 $ 49,734
Weighted-Average Remaining Lease Term and Weighted-Average Discount Rate of Operating Leases	The weighted-average remaining lease term and weighted-average discount rate of the Company’s operating leases were as follows: As of September 30, 2020 Weighted-average remaining lease term (years) 13.8 Weighted-average discount rate 5.4 %
Reconciliation of Undiscounted Future Minimum Lease Payments Remaining Operating Leases	The following table presents a reconciliation of the undiscounted future minimum lease payments remaining the Company’s operating leases to the amounts reported as operating lease liabilities on the consolidated balance sheet as of September 30, 2020 (in thousands): As of September 30, 2020 Undiscounted future minimum lease payments: 2020 (remainder of year) $ 1,117 2021 3,964 2022 5,055 2023 6,980 2024 8,000 Thereafter 99,184 Total undiscounted future minimum lease payments $ 124,300 Amount representing imputed interest (45,843 ) Tenant improvement allowance not yet received (17,432 ) Total operating lease liabilities 61,025 Current portion of operating lease liabilities (3,564 ) Operating lease liabilities, non-current $ 57,461

License and Royalty Revenue (Ta

License and Royalty Revenue (Tables)	9 Months Ended
	Sep. 30, 2020
License Agreement Revenue Recognition [Abstract]
Summary of Changes in Balances of Receivables, Contract Assets and Deferred Revenue	The following table presents changes in the balances of the Company’s receivables, contract assets and deferred revenue, as well as other information regarding revenue recognized during the periods presented (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Accounts receivable, current and non-current: Balance, beginning of period $ 46,494 $ 33,634 $ 42,303 $ 31,599 Additions 100,243 15,526 137,220 26,575 Deductions (21,057 ) (5,640 ) (53,843 ) (14,654 ) Balance, end of period $ 125,680 $ 43,520 $ 125,680 $ 43,520 Contract assets: Balance, beginning of period $ 350 $ — $ — $ 750 Additions — — 350 1,000 Deductions — — — (1,750 ) Balance, end of period $ 350 $ — $ 350 $ — Deferred revenue, current and non-current: Balance, beginning of period $ 4,457 $ 3,333 $ 3,333 $ 3,933 Additions — — 1,124 — Deductions (113 ) — (113 ) (600 ) Balance, end of period $ 4,344 $ 3,333 $ 4,344 $ 3,333 Revenue recognized during the period from: Amounts included in deferred revenue at beginning of period $ 113 $ — $ — $ 600 Performance obligations satisfied in previous periods $ 98,799 $ 10,072 $ 125,555 $ 15,037
Summary of Accounts Receivables, net	Accounts receivable, net consisted of the following (in thousands): September 30, 2020 December 31, 2019 Current accounts receivable: Billed to customers $ 30,086 $ 376 Unbilled 99,708 37,772 Allowance for credit losses (7,678 ) — Current accounts receivable, net 122,116 38,148 Non-current accounts receivable: Unbilled 3,564 4,155 Allowance for credit losses — — Non-current accounts receivable, net 3,564 4,155 Total accounts receivable, net $ 125,680 $ 42,303
Summary of Changes in Allowance For Credit Losses	The following table presents the changes in the allowance for credit losses related to accounts receivable and contract assets for the nine months ended September 30, 2020 (in thousands): Accounts Receivable Contract Assets Balance at December 31, 2019 $ — $ — Provision for credit losses 7,678 — Write-offs — — Balance at September 30, 2020 $ 7,678 $ —
Schedule of License Revenue	The Company recognized the following amounts under the March 2014 License with AveXis (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 License revenue $ — $ — $ 3,500 $ 3,500 Royalties on net sales of Zolgensma 18,799 9,182 40,723 10,106 Achievement of sales-based milestone for Zolgensma 80,000 — 80,000 — Total license and royalty revenue $ 98,799 $ 9,182 $ 124,223 $ 13,606 Interest income from licensing $ 6 $ 7 $ 20 $ 22

Stock-based Compensation (Table

Stock-based Compensation (Tables)	9 Months Ended
	Sep. 30, 2020
Stock-Based Compensation Expense by Award Type	The Company’s stock-based compensation expense by award type was as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Stock options $ 7,880 $ 6,965 $ 23,745 $ 19,261 Restricted stock units — 69 — 206 Employee stock purchase plan 155 128 623 512 $ 8,035 $ 7,162 $ 24,368 $ 19,979
Stock-Based Compensation Expense	The Company has recorded aggregate stock-based compensation expense in the consolidated statements of operations and comprehensive income (loss) as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Research and development $ 4,110 $ 3,657 $ 12,442 $ 9,530 General and administrative 3,925 3,505 11,926 10,449 $ 8,035 $ 7,162 $ 24,368 $ 19,979
2014 and 2015 Equity Incentive Plan [Member]
Summary of Stock Option Activity	The following table summarizes stock option activity under the 2014 Plan and 2015 Plan (in thousands, except per share data): Weighted- average Weighted- Remaining average Contractual Aggregate Exercise Life Intrinsic Shares Price (Years) Value (a) Outstanding at December 31, 2019 5,544 $ 28.79 7.5 $ 86,509 Granted 1,542 $ 38.25 Exercised (356 ) $ 11.92 Cancelled or forfeited (321 ) $ 45.11 Outstanding at September 30, 2020 6,409 $ 31.18 7.4 $ 37,396 Exercisable at September 30, 2020 3,581 $ 23.34 6.3 $ 36,885 Vested and expected to vest at September 30, 2020 6,409 $ 31.18 7.4 $ 37,396 (a) The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying options and the fair value of the common stock for the options that were in the money at the dates reported.

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Computations of Basic and Diluted Net Income (Loss) Per Share	The computations of basic and diluted net income (loss) per share were as follows (in thousands, except per share data): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Basic net income (loss) per share: Net income (loss) $ 8,791 $ (34,584 ) $ (65,009 ) $ (68,269 ) Shares used in computation: Weighted-average common shares outstanding 37,342 36,813 37,234 36,618 Basic net income (loss) per share $ 0.24 $ (0.94 ) $ (1.75 ) $ (1.86 ) Diluted net income (loss) per share: Net income (loss) $ 8,791 $ (34,584 ) $ (65,009 ) $ (68,269 ) Shares used in computation: Weighted-average common shares outstanding 37,342 36,813 37,234 36,618 Stock options 1,529 — — — Employee stock purchase plan 6 — — — Weighted-average diluted common shares 38,877 36,813 37,234 36,618 Diluted net income (loss) per share $ 0.23 $ (0.94 ) $ (1.75 ) $ (1.86 )
Schedules for Computation of Diluted Weighted-Average Shares Outstanding	The following potentially dilutive common stock equivalents outstanding at the end of the period were excluded from the computations of weighted-average diluted common shares for the periods indicated as their effects would be anti-dilutive (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Stock options issued and outstanding 4,072 5,530 6,409 5,530 Unvested restricted stock units outstanding — 40 — 40 Employee stock purchase plan — 16 21 16 4,072 5,586 6,430 5,586

Supplemental Disclosures (Table

Supplemental Disclosures (Tables)	9 Months Ended
	Sep. 30, 2020
Payables And Accruals [Abstract]
Schedules of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of the following (in thousands): September 30, 2020 December 31, 2019 Accrued sublicense fees and royalties $ 19,285 $ 4,542 Accrued personnel costs 10,380 10,903 Accrued external research and development expenses 9,163 5,791 Accrued external general and administrative expenses 2,873 2,053 Accrued purchases of property and equipment 2,438 1,328 Other accrued expenses and current liabilities 217 229 $ 44,356 $ 24,846

Nature of Business - Additional

Nature of Business - Additional Information (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Accumulated deficit	$ (242,831)	$ (177,822)
Cash, cash equivalents and marketable securities	$ 289,800

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Summary of Reconciliation of Cash and Cash Equivalents and Restricted Cash (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Accounting Policies [Abstract]
Cash and cash equivalents	$ 93,220	$ 69,514	$ 79,594
Restricted cash	1,330	$ 1,330	1,053
Total cash and cash equivalents and restricted cash	$ 94,550		$ 80,647

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Additional Information (Detail)	Sep. 30, 2020USD ($)
Accounting Policies [Abstract]
Allowance for credit losses on available-for-sale debt securities	$ 0

Marketable Securities - Summary

Marketable Securities - Summary of Company Marketable Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost / Cost	$ 184,145	$ 297,631
Unrealized Gains	12,443	32,884
Unrealized Losses	(11)	(34)
Fair Value	196,577	330,481
U.S. Government and Federal Agency Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost / Cost	20,802	62,637
Unrealized Gains	77	215
Unrealized Losses		(5)
Fair Value	20,879	62,847
Certificates of Deposit [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost / Cost	3,416	8,506
Unrealized Gains	51	77
Fair Value	3,467	8,583
Corporate Bonds [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost / Cost	159,732	226,137
Unrealized Gains	1,007	808
Unrealized Losses	(11)	(29)
Fair Value	160,728	226,916
Equity Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost / Cost	195	351
Unrealized Gains	11,308	31,784
Fair Value	$ 11,503	$ 32,135

Marketable Securities - Additio

Marketable Securities - Additional Information (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2020USD ($)Security	Sep. 30, 2019USD ($)	Sep. 30, 2020USD ($)Security	Sep. 30, 2019USD ($)	Dec. 31, 2019USD ($)
Schedule Of Available For Sale Securities [Line Items]
Available for sale debt securities remaining maturities greater than three years	$ 0		$ 0		$ 0
Unrealized gains (losses) on available-for-sale debt securities, before tax	$ (500,000)	$ (100,000)	$ 100,000	$ 1,700,000
Number of investment grade fixed income debt security | Security	5		5
Other-than-temporary impaired			$ 0
Non-marketable equity securities, carrying value	$ 400,000		400,000
Equity Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Marketable securities, unrealized gain (loss)	(8,300,000)	(2,200,000)	(8,300,000)	29,400,000
Marketable securities, realized gain	7,500,000	0	7,500,000	0
Maximum [Member]
Schedule Of Available For Sale Securities [Line Items]
Unrealized gains (losses) on available-for-sale debt securities, income tax benefit (expense)	0	100,000	0	(600,000)
Investment Income [Member] | Maximum [Member]
Schedule Of Available For Sale Securities [Line Items]
Net realized gains (losses) available for sale securities	$ 100,000	$ 100,000	$ 100,000	$ 100,000

Marketable Securities - Summa_2

Marketable Securities - Summary of Fair Values and Unrealized Losses of Marketable Securities Held by the Company in an Unrealized Loss Position for Less Than 12 months and 12 Months or Greater (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
Schedule Of Available For Sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 13,728
Less than 12 Months, Unrealized Losses	(11)	$ (34)
Total, Fair Value	13,728
Total, Unrealized Losses	(11)	(34)
Less than 12 Months, Fair Value		61,118
Total, Fair Value		61,118
Corporate Bonds [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than 12 Months, Fair Value	13,728
Less than 12 Months, Unrealized Losses	(11)	(29)
Total, Fair Value	13,728
Total, Unrealized Losses	$ (11)	(29)
Less than 12 Months, Fair Value		48,556
Total, Fair Value		48,556
U.S. Government and Federal Agency Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than 12 Months, Unrealized Losses		(5)
Total, Unrealized Losses		(5)
Less than 12 Months, Fair Value		12,562
Total, Fair Value		$ 12,562

Fair Value of Financial Instr_3

Fair Value of Financial Instruments - Schedule of Fair Value of Cash Equivalents and Marketable Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Marketable securities:
Fair Value	$ 196,577	$ 330,481
Cash Equivalents and Marketable Securities [Member]
Marketable securities:
Total cash equivalents and marketable securities	267,382	386,539
Corporate Bonds [Member]
Marketable securities:
Fair Value	160,728	226,916
Cash Equivalents [Member]
Cash equivalents:
Total cash equivalents	70,805	56,058
U.S. Government and Federal Agency Securities [Member]
Marketable securities:
Fair Value	20,879	62,847
Certificates of Deposit [Member]
Marketable securities:
Fair Value	3,467	8,583
Equity Securities [Member]
Marketable securities:
Fair Value	11,503	32,135
Money Market Mutual Funds [Member] | Cash Equivalents [Member]
Cash equivalents:
Total cash equivalents	70,805	56,058
Quoted Prices in Active Markets (Level 1) [Member]
Marketable securities:
Fair Value	11,503	32,135
Quoted Prices in Active Markets (Level 1) [Member] | Cash Equivalents and Marketable Securities [Member]
Marketable securities:
Total cash equivalents and marketable securities	11,503	32,135
Quoted Prices in Active Markets (Level 1) [Member] | Equity Securities [Member]
Marketable securities:
Fair Value	11,503	32,135
Significant Other Observable Inputs (Level 2) [Member]
Marketable securities:
Fair Value	185,074	298,346
Significant Other Observable Inputs (Level 2) [Member] | Cash Equivalents and Marketable Securities [Member]
Marketable securities:
Total cash equivalents and marketable securities	255,879	354,404
Significant Other Observable Inputs (Level 2) [Member] | Corporate Bonds [Member]
Marketable securities:
Fair Value	160,728	226,916
Significant Other Observable Inputs (Level 2) [Member] | Cash Equivalents [Member]
Cash equivalents:
Total cash equivalents	70,805	56,058
Significant Other Observable Inputs (Level 2) [Member] | U.S. Government and Federal Agency Securities [Member]
Marketable securities:
Fair Value	20,879	62,847
Significant Other Observable Inputs (Level 2) [Member] | Certificates of Deposit [Member]
Marketable securities:
Fair Value	3,467	8,583
Significant Other Observable Inputs (Level 2) [Member] | Money Market Mutual Funds [Member] | Cash Equivalents [Member]
Cash equivalents:
Total cash equivalents	$ 70,805	$ 56,058

Fair Value of Financial Instr_4

Fair Value of Financial Instruments - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Non-marketable equity securities	$ 1,100,000		$ 1,100,000		$ 0
Remeasurements or impairment losses on non-marketable equity securities	$ 0	$ 0	$ 0	$ 0

Property and Equipment Net - Sc

Property and Equipment Net - Schedule of Property and Equipment (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Property Plant And Equipment [Line Items]
Total property and equipment	$ 59,441	$ 43,311
Accumulated depreciation and amortization	(20,570)	(14,338)
Property and equipment, net	38,871	28,973
Laboratory and Manufacturing Equipment [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	23,162	19,663
Computer Equipment and Software [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	3,272	2,545
Furniture and Fixtures [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	2,898	2,188
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	$ 30,109	$ 18,915

Leases - Additional Information

Leases - Additional Information (Detail) $ in Thousands	1 Months Ended						3 Months Ended	9 Months Ended
	Nov. 30, 2020USD ($)	Oct. 31, 2020USD ($)	Aug. 31, 2018USD ($)ft²	Apr. 30, 2018USD ($)	May 31, 2016USD ($)	Jan. 31, 2016USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Dec. 31, 2019USD ($)
Other Commitments [Line Items]
Property and equipment, net							$ 38,871	$ 38,871		$ 28,973
Operating lease right-of-use assets							57,827	57,827		$ 10,078
Lease liabilities							61,025	61,025
Decrease in right-of-use assets								(1,986)	$ (1,712)
Operating lease liabilities								$ (2,222)	$ (1,832)
Rockville, Maryland [Member]
Other Commitments [Line Items]
Operating lease expiration year								2028
9804 Medical Center Drive [Member]
Other Commitments [Line Items]
Tenant improvement allowance received								$ 19,500
Tenant improvement allowance receivable							17,200	17,200
Property and equipment, net							17,300	17,300
Operating lease right-of-use assets							50,600	50,600
Lease liabilities							52,500	$ 52,500
9804 Medical Center Drive [Member] | Rockville, Maryland [Member]
Other Commitments [Line Items]
Minimum release term for option to terminate			12 years
Construction completion, description								The initial construction of the building was performed by the landlord, and the lease commenced in September 2020 upon the delivery of leased premises to the Company to make additional improvements to the building.
Lease not yet commenced, additional lease term			10 years
Lease not yet commenced, option to terminate the lease								true
Letters of credit			$ 1,100
Number of square feet to be constructed | ft²			177,000
Lease not yet commenced, option to terminate the lease, description								The Company has the option to extend the term of the lease for up to 10 additional years and the option to terminate the lease, with payment of an early termination fee, after 12 years from the delivery of the leased premises to the Company.
Lease commenced date			2020-09
Lease expiration date			Sep. 30, 2036
9712 Medical Center Drive [Member] | Rockville, Maryland [Member] | Subsequent Event [Member]
Other Commitments [Line Items]
Additional lease term under option to extend		3 years
Additional lease payments		$ 8,800
9712 Medical Center Drive [Member] | Rockville, Maryland [Member]
Other Commitments [Line Items]
Tenant improvement allowance received				$ 400
Lease term								In September 2015, November 2015, July 2017 and April 2018, the Company amended the 9712 Medical Center Drive Lease to include additional office and laboratory space at 9714 Medical Center Drive, and ultimately extend the term of the lease to September 2021.
Operating lease, existence of option to extend the lease								true
Additional lease term under option to extend				6 years
9600 Blackwell Road [Member]
Other Commitments [Line Items]
Reduction in expected exercise of termination rights							$ 700	$ 700
9600 Blackwell Road [Member] | Rockville, Maryland [Member]
Other Commitments [Line Items]
Lease commenced date						2016-02
Lease expiration date						Sep. 30, 2023
Tenant improvement allowance received						$ 800
Operating lease, existence of option to extend the lease								true
Additional lease term under option to extend						5 years
Required period to terminate lease after commencement period						67 months
Decrease in right-of-use assets						$ 700
Operating lease liabilities						$ 700
9600 Blackwell Road [Member] | Rockville, Maryland [Member] | Scenario Forecast [Member]
Other Commitments [Line Items]
Lease expiration date	Sep. 30, 2021
Early termination fee	$ 400
400 Madison Avenue [Member] | 400 Madison Lease [Member]
Other Commitments [Line Items]
Letters of credit					$ 200
Operating leases commencement year					2016-07
Tenant improvement allowance entitled to received					$ 700

Leases - Summary of Lease Costs

Leases - Summary of Lease Costs and Supplemental Cash Flow Information of Operating Leases (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020
Leases [Abstract]
Operating lease cost	$ 997	$ 2,793
Variable lease cost	174	575
Total lease cost	1,171	3,368
Cash paid for amounts included in operating lease liabilities	988	2,482
Right-of-use assets acquired through operating lease liabilities	$ 49,734	$ 49,734

Leases - Weighted-Average Remai

Leases - Weighted-Average Remaining Lease Term and Weighted-Average Discount Rate of Operating Leases (Detail)	Sep. 30, 2020
Leases [Abstract]
Weighted-average remaining lease term (years)	13 years 9 months 18 days
Weighted-average discount rate	5.40%

Leases - Reconciliation of Undi

Leases - Reconciliation of Undiscounted Future Minimum Lease Payments Remaining Operating Leases (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Undiscounted future minimum lease payments:
2020 (remainder of year)	$ 1,117
2021	3,964
2022	5,055
2023	6,980
2024	8,000
Thereafter	99,184
Total undiscounted future minimum lease payments	124,300
Amount representing imputed interest	(45,843)
Tenant improvement allowance not yet received	(17,432)
Total operating lease liabilities	61,025
Current portion of operating lease liabilities	(3,564)	$ (2,421)
Operating lease liabilities, non-current	$ 57,461	$ 8,874

License and Royalty Revenue - A

License and Royalty Revenue - Additional Information (Detail) $ in Thousands	May 31, 2020USD ($)	Apr. 01, 2020USD ($)	Nov. 30, 2018	Oct. 31, 2020USD ($)	Nov. 30, 2018	Sep. 30, 2020USD ($)ProductCandidate	Sep. 30, 2019USD ($)	Sep. 30, 2020USD ($)ProductCandidate	Sep. 30, 2019USD ($)	Jun. 30, 2020USD ($)	Dec. 31, 2019USD ($)	Jun. 30, 2019USD ($)	Dec. 31, 2018USD ($)
License Revenue [Line Items]
Milestone fee upon submission of preclinical regulatory filings								$ 300
Milestone payment upon commencement of clinical trials in humans								26,600
Milestone payment upon submission of regulatory approval filings								26,000
Milestone payment upon approval of commercial products by regulatory agencies								103,500
Milestone payment upon achievement of specified sales targets for licensed products								57,000
Deferred revenue, current and non-current						$ 4,344	$ 3,333	4,344	$ 3,333	$ 4,457	$ 3,333	$ 3,333	$ 3,933
Provision for credit losses						7,700	0	7,678	0
Accounts receivable						125,680	$ 43,520	125,680	$ 43,520	$ 46,494	42,303	$ 33,634	$ 31,599
AveXis, Inc. [Member]
License Revenue [Line Items]
Milestone payment upon achievement of specified sales targets for licensed products								1,000,000
Aggregate milestone payment for all the targets								80,000
Accounts receivable						80,000		80,000
AveXis, Inc. [Member] | March 2014 License Agreement [Member]
License Revenue [Line Items]
Accounts receivable						98,900		98,900			11,000
Accounts receivable, current						98,800		98,800			10,800
Accounts receivable, non -current						100		100			$ 200
AveXis, Inc. [Member] | Subsequent Event [Member]
License Revenue [Line Items]
Milestone payments				$ 80,000
Abeona Therapeutics Inc. [Member] | November 2018 License Agreement Termination [Member]
License Revenue [Line Items]
Up-front and anuual fees		$ 20,000
Abeona Therapeutics Inc. [Member] | November 2018 License Agreement [Member]
License Revenue [Line Items]
License fee		$ 8,000
Abeona Therapeutics Inc. [Member] | November 2018 License Agreement [Member] | November 2018 License Agreement Termination [Member]
License Revenue [Line Items]
Accounts receivable	$ 28,000					30,100		30,100
License fee				$ 28,000
License agreement termination claims, description	subsequent to the termination of the November 2018 License, Abeona filed a claim in arbitration alleging that the Company had breached certain responsibilities to communicate with Abeona regarding the Company’s prosecution of licensed patents under the November 2018 License. The Company disputes Abeona’s claim and has filed a counterclaim in arbitration demanding payment of the $28.0 million of unpaid fees from Abeona, plus accrued interest.		As a result of the termination, Abeona was required to pay a $20.0 million license fee to the Company within 15 days of the termination date, which otherwise would have been due to the Company in November 2020.
Interest percentage on unpaid balances under license agreement					1.50%
Interest income from license on unpaid license fees						1,300		2,100
Allowance for doubtful accounts receivable						$ 7,700		7,700
Maximum [Member]
License Revenue [Line Items]
Aggregate milestone payment for all the targets								$ 213,400
N A V Technology Platform [Member]
License Revenue [Line Items]
Number of commercial product candidates | ProductCandidate						1		1
N A V Technology Platform [Member] | Minimum [Member]
License Revenue [Line Items]
Number of development partnered product candidates | ProductCandidate						20		20
Zolgensma [Member]
License Revenue [Line Items]
Accounts receivable						$ 1,000,000		$ 1,000,000

License and Royalty Revenue - S

License and Royalty Revenue - Summary of Changes in Balances of Receivables, Contract Assets and Deferred Revenue (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accounts receivable, current and non-current:
Balance, beginning of period	$ 46,494	$ 33,634	$ 42,303	$ 31,599
Additions	100,243	15,526	137,220	26,575
Deductions	(21,057)	(5,640)	(53,843)	(14,654)
Balance, end of period	125,680	43,520	125,680	43,520
Contract assets:
Balance, beginning of period	350			750
Additions			350	1,000
Deductions				(1,750)
Balance, end of period	350		350
Deferred revenue, current and non-current:
Balance, beginning of period	4,457	3,333	3,333	3,933
Additions			1,124
Deductions	(113)		(113)	(600)
Balance, end of period	4,344	3,333	4,344	3,333
Revenue recognized during the period from:
Amounts included in deferred revenue at beginning of period	113			600
Performance obligations satisfied in previous periods	$ 98,799	$ 10,072	$ 125,555	$ 15,037

License and Royalty Revenue -_2

License and Royalty Revenue - Summary of Accounts Recerivable, Net (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Current accounts receivable:
Billed to customers	$ 30,086	$ 376
Unbilled	99,708	37,772
Allowance for credit losses	(7,678)
Current accounts receivable, net	122,116	38,148
Non-current accounts receivable:
Unbilled	3,564	4,155
Non-current accounts receivable, net	3,564	4,155
Total accounts receivable, net	$ 125,680	$ 42,303

License and Royalty Revenue -_3

License and Royalty Revenue - Summary of Changes in Allowance For Credit Losses (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2020USD ($)
Accounts Receivable [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning Balance
Provision for credit losses	7,678
Write-offs
Ending Balance	7,678
Contract Assets [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning Balance
Provision for credit losses
Write-offs
Ending Balance

License and Royalty Revenue -_4

License and Royalty Revenue - Schedule Of License Revenue (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
License Revenue [Line Items]
Total license and royalty revenue	$ 98,799	$ 9,182	$ 124,223	$ 13,606
Interest income from licensing	1,444	716	4,141	2,091
AveXis, Inc. [Member]
License Revenue [Line Items]
Interest income from licensing	6	7	20	22
License [Member]
License Revenue [Line Items]
Total license and royalty revenue			3,500	3,500
Zolgensma Royalties [Member]
License Revenue [Line Items]
Total license and royalty revenue	18,799	$ 9,182	40,723	$ 10,106
Achievement of Sales Based Milestone for Zolgensma [Member]
License Revenue [Line Items]
Total license and royalty revenue	$ 80,000		$ 80,000

Stock-based Compensation - Addi

Stock-based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	9 Months Ended
	Jan. 31, 2020	Sep. 30, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation expense		$ 68.6
Unrecognized stock-based compensation, weighted-average period		2 years 6 months
Proceeds from stock options exercised including unsettled options		$ 4.2
2015 Equity Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Additional shares to be issued	1,479,696
Common stock shares authorized for issuance		12,412,917
Shares available for future grants		2,321,306
Weighted-average fair values of options granted		$ 24.08
Exercise of stock options, Shares		356,302
Total intrinsic value of options exercised		$ 9.4
2015 Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Additional shares to be issued	369,924
Common stock shares authorized for issuance		623,924
Shares available for future grants		448,011
Common stock shares issued to participants		55,499

Stock-based Compensation - Stoc

Stock-based Compensation - Stock-Based Compensation Expense by Award Type (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 8,035	$ 7,162	$ 24,368	$ 19,979
Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	7,880	6,965	23,745	19,261
Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense		69		206
Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 155	$ 128	$ 623	$ 512

Stock-based Compensation - St_2

Stock-based Compensation - Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 8,035	$ 7,162	$ 24,368	$ 19,979
Research and Development [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	4,110	3,657	12,442	9,530
General and Administrative [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 3,925	$ 3,505	$ 11,926	$ 10,449

Stock-based Compensation - Summ

Stock-based Compensation - Summary of Stock Option Activity (Detail) - 2014 and 2015 Equity Incentive Plan [Member] $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020USD ($)$ / sharesshares	Dec. 31, 2019USD ($)$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares [Roll Forward]
Shares Outstanding, Beginning Balance | shares	5,544
Shares, Granted | shares	1,542
Shares, Exercised | shares	(356)
Shares, Cancelled or forfeited | shares	(321)
Shares Outstanding, Ending Balance | shares	6,409	5,544
Shares, Exercisable | shares	3,581
Shares, Vested and expected to vest | shares	6,409
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted-average Exercise Price Outstanding, Beginning Balance | $ / shares	$ 28.79
Weighted-average Exercise Price, Granted | $ / shares	38.25
Weighted-average Exercise Price, Exercised | $ / shares	11.92
Weighted-average Exercise Price, Cancelled or forfeited | $ / shares	45.11
Weighted-average Exercise Price, Outstanding, Ending Balance | $ / shares	31.18	$ 28.79
Weighted-average Exercise Price, Exercisable | $ / shares	23.34
Weighted-average Exercise Price, Vested and expected to vest | $ / shares	$ 31.18
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted-average Remaining Contractual Life (Years) Outstanding	7 years 4 months 24 days	7 years 6 months
Weighted-average Remaining Contractual Life (Years), Exercisable	6 years 3 months 19 days
Weighted-average Remaining Contractual Life (Years), Vested and expected to vest	7 years 4 months 24 days
Aggregate Intrinsic Value Outstanding | $	$ 37,396	$ 86,509
Aggregate Intrinsic Value, Exercisable | $	36,885
Aggregate Intrinsic Value, Vested and expected to vest | $	$ 37,396

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2020USD ($)
Income Tax Disclosure [Abstract]
Elimination of limitation in net operating losses deductions as percentage of current year taxable income, percentage	80.00%
Recovery period on qualified improvement of property	15 years
Current income tax benefit	$ 0.5

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
FOXKISER LLP [Member] | Service Agreements [Member] | Research and Development [Member]
Related Party Transaction [Line Items]
Related party transaction expense	$ 1.2	$ 1.2	$ 3.6	$ 2.9

Net Loss Per Share - Computatio

Net Loss Per Share - Computations of Basic and Diluted Net Income (Loss) Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Basic net income (loss) per share:
Net income (loss)	$ 8,791	$ (34,584)	$ (65,009)	$ (68,269)
Shares used in computation:
Weighted-average common shares outstanding	37,342	36,813	37,234	36,618
Basic net income (loss) per share	$ 0.24	$ (0.94)	$ (1.75)	$ (1.86)
Diluted net income (loss) per share:
Net income (loss)	$ 8,791	$ (34,584)	$ (65,009)	$ (68,269)
Shares used in computation:
Weighted-average common shares outstanding	37,342	36,813	37,234	36,618
Weighted-average diluted common shares	38,877	36,813	37,234	36,618
Diluted net income (loss) per share	$ 0.23	$ (0.94)	$ (1.75)	$ (1.86)
Stock Option [Member]
Shares used in computation:
Weighted-average diluted common shares	1,529
Employee Stock Purchase Plan [Member]
Shares used in computation:
Weighted-average diluted common shares	6

Net Loss Per Share - Schedules

Net Loss Per Share - Schedules for Computation of Diluted Weighted-Average Shares Outstanding (Detail) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted weighted average shares outstanding	4,072	5,586	6,430	5,586
Stock Options Issued and Outstanding [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted weighted average shares outstanding	4,072	5,530	6,409	5,530
Unvested Restricted Stock Units Outstanding [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted weighted average shares outstanding		40		40
Employee Stock Purchase Plan [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted weighted average shares outstanding		16	21	16

Supplemental Disclosures - Sche

Supplemental Disclosures - Schedules of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Payables And Accruals [Abstract]
Accrued sublicense fees and royalties	$ 19,285	$ 4,542
Accrued personnel costs	10,380	10,903
Accrued external research and development expenses	9,163	5,791
Accrued external general and administrative expenses	2,873	2,053
Accrued purchases of property and equipment	2,438	1,328
Other accrued expenses and current liabilities	217	229
Accrued expenses and other current liabilities	$ 44,356	$ 24,846