REGENXBIO (RGNX) 10-Q 5 Nov 19 2019 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2019	Nov. 01, 2019
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2019
Document Fiscal Year Focus	2019
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		36,874,282
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, 2019	Dec. 31, 2018
Current assets
Cash and cash equivalents	$ 79,594	$ 75,561
Marketable securities	252,125	244,200
Accounts receivable	19,175	8,587
Prepaid expenses	6,920	5,734
Other current assets	2,414	3,831
Total current assets	360,228	337,913
Marketable securities	85,408	150,819
Accounts receivable	24,345	23,012
Property and equipment, net	28,287	28,702
Operating lease right-of-use assets	5,905
Restricted cash	1,053	1,053
Other assets	4,011	2,315
Total assets	509,237	543,814
Current liabilities
Accounts payable	9,608	4,412
Accrued expenses and other current liabilities	19,231	17,164
Deferred revenue		600
Operating lease liabilities	2,506
Total current liabilities	31,345	22,176
Deferred revenue	3,333	3,333
Operating lease liabilities	4,320
Deferred rent		1,098
Financing lease obligations		5,854
Other liabilities	1,844	2,505
Total liabilities	40,842	34,966
Commitments and contingencies (Note 7)
Stockholders’ equity
Preferred stock; $0.0001 par value; 10,000 shares authorized, and no shares issued and outstanding at September 30, 2019 and December 31, 2018
Common stock; $0.0001 par value; 100,000 shares authorized at September 30, 2019 and December 31, 2018; 36,840 and 36,120 shares issued and outstanding at September 30, 2019 and December 31, 2018, respectively	4	4
Additional paid-in capital	619,386	592,580
Accumulated other comprehensive income (loss)	363	(720)
Accumulated deficit	(151,358)	(83,016)
Total stockholders’ equity	468,395	508,848
Total liabilities and stockholders’ equity	$ 509,237	$ 543,814

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2019	Dec. 31, 2018
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	36,840,000	36,120,000
Common stock, shares outstanding	36,840,000	36,120,000

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenues
Revenues	$ 14,700	$ 5,306	$ 23,465	$ 177,728
Types of Revenue[Extensible List]	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Operating Expenses
Cost of revenues	$ 2,494	$ 517	$ 4,450	$ 6,797
Research and development	35,692	18,508	90,378	59,544
General and administrative	12,402	9,008	37,365	25,706
Other operating expenses (income)	8	(2)	(54)	31
Total operating expenses	50,596	28,031	132,139	92,078
Income (loss) from operations	(35,896)	(22,725)	(108,674)	85,650
Other Income
Interest income from licensing	716	109	2,091	8,362
Investment income	431	2,122	37,950	4,177
Total other income	1,147	2,231	40,041	12,539
Income (loss) before income taxes	(34,749)	(20,494)	(68,633)	98,189
Income Tax Benefit (Expense)	165	1,292	364	(2,558)
Net income (loss)	(34,584)	(19,202)	(68,269)	95,631
Other Comprehensive Income (Loss)
Unrealized gain (loss) on available-for-sale securities, net of reclassifications and income tax expense	(108)	(103)	1,043	(159)
Total other comprehensive income (loss)	(108)	(103)	1,043	(159)
Comprehensive income (loss)	(34,692)	(19,305)	(67,226)	95,472
Net income (loss) applicable to common stockholders	$ (34,584)	$ (19,202)	$ (68,269)	$ 95,631
Net income (loss) per share:
Basic	$ (0.94)	$ (0.56)	$ (1.86)	$ 2.94
Diluted	$ (0.94)	$ (0.56)	$ (1.86)	$ 2.67
Weighted-average common shares outstanding:
Basic	36,813	33,988	36,618	32,576
Diluted	36,813	33,988	36,618	35,875

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional paid in capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]
Balances at Dec. 31, 2017	$ 183,029	$ 3	$ 371,497	$ (715)	$ (187,756)
Balances (Shares) at Dec. 31, 2017		31,295
Adoption of ASU | ASU 2014-09 [Member]	4,803				4,803
Issuance of common stock upon public offering, net of transaction costs, values	189,097	$ 1	189,096
Issuance of common stock upon public offering, net of transaction costs, shares		3,105
Exercise of stock options	9,051		9,051
Exercise of stock options, Shares		1,267
Issuance of common stock under employee stock purchase plan	850		850
Issuance of common stock under employee stock purchase plan, shares		37
Stock-based compensation expense	11,755		11,755
Unrealized gain (loss) on available-for-sale securities, net of reclassifications and income tax expense	(159)			(159)
Net income (loss)	95,631				95,631
Balances at Sep. 30, 2018	494,057	$ 4	582,249	(874)	(87,322)
Balances (Shares) at Sep. 30, 2018		35,704
Balances at Jun. 30, 2018	317,222	$ 3	386,110	(771)	(68,120)
Balances (Shares) at Jun. 30, 2018		32,275
Issuance of common stock upon public offering, net of transaction costs, values	189,097	$ 1	189,096
Issuance of common stock upon public offering, net of transaction costs, shares		3,105
Exercise of stock options	2,053		2,053
Exercise of stock options, Shares		307
Issuance of common stock under employee stock purchase plan	507		507
Issuance of common stock under employee stock purchase plan, shares		17
Stock-based compensation expense	4,483		4,483
Unrealized gain (loss) on available-for-sale securities, net of reclassifications and income tax expense	(103)			(103)
Net income (loss)	(19,202)				(19,202)
Balances at Sep. 30, 2018	494,057	$ 4	582,249	(874)	(87,322)
Balances (Shares) at Sep. 30, 2018		35,704
Balances at Dec. 31, 2018	508,848	$ 4	592,580	(720)	(83,016)
Balances (Shares) at Dec. 31, 2018		36,120
Adoption of ASU | ASU 2016-02 [Member]	(33)				(33)
Adoption of ASU | ASU 2018-02 [Member]				40	(40)
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 of reclassifications and income tax expense	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 of reclassifications and income tax expense	(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

Consolidated Statements of St_2

Consolidated Statements of Stockholders' Equity (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2019
Common Stock [Member]
Issuance of Stock, transaction costs	$ 12,728	$ 12,728

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities
Net income (loss)	$ (68,269)	$ 95,631
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities
Stock-based compensation expense	19,979	11,755
Net amortization of premiums and accretion of discounts on marketable debt securities	(1,085)	889
Depreciation and amortization	5,229	2,671
Net realized losses (gains) on sales and maturities of marketable securities	(20)	15
Imputed interest income from licensing	(2,091)	(8,362)
Unrealized gains on marketable equity securities	(29,420)
Other non-cash adjustments	357	12
Changes in operating assets and liabilities
Accounts receivable	(10,699)	6,986
Prepaid expenses	(1,418)	(974)
Other current assets	1,286	(3,072)
Operating lease right-of-use assets	1,712
Other assets	(2,150)	(788)
Accounts payable	5,339	156
Accrued expenses and other current liabilities	1,990	3,438
Deferred revenue	(600)	600
Operating lease liabilities	(1,832)
Deferred rent		(41)
Other liabilities	(507)	(128)
Net cash provided by (used in) operating activities	(82,199)	108,788
Cash flows from investing activities
Purchases of marketable securities	(127,925)	(319,897)
Maturities of marketable securities	218,019	116,110
Purchases of property and equipment	(10,689)	(8,389)
Net cash provided by (used in) investing activities	79,405	(212,176)
Cash flows from financing activities
Proceeds from exercise of stock options	5,513	9,051
Proceeds from issuance of common stock under employee stock purchase plan	1,314	850
Proceeds from public offerings of common stock, net of underwriting discounts and commissions		189,716
Issuance costs for public offerings of common stock		(462)
Net cash provided by financing activities	6,827	199,155
Net increase in cash and cash equivalents and restricted cash	4,033	95,767
Cash and cash equivalents and restricted cash
Beginning of period	76,614	46,881
End of period	$ 80,647	142,648
Supplemental disclosures of non-cash investing and financing activities
Purchases of property and equipment in accounts payable and accrued expenses		174
Issuance costs for public offerings of common stock in accounts payable and accrued expenses		$ 157

Nature of Business

Nature of Business	9 Months Ended
	Sep. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Nature of Business	1. Nature of Business REGENXBIO Inc. (the Company) is a leading 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 Company’s 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 candidates in multiple therapeutic areas. The Company was formed in 2008 in the State of Delaware and is headquartered in Rockville, Maryland. Liquidity and Risks As of September 30, 2019, the Company had generated an accumulated deficit of $151.4 million since inception. As the Company has incurred cumulative losses since inception, transition to recurring profitability is dependent upon the successful development, approval and commercialization of its product candidates and achieving a level of revenues adequate to support the Company’s cost structure. The Company may never achieve recurring profitability, and unless and until it does, the Company will continue to need to raise additional capital. As of September 30, 2019, the Company had cash, cash equivalents and marketable securities of $417.1 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, 2019
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, 2018 included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018, which was filed with the SEC on February 27, 2019. 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, 2018, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018. 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, stock-based compensation expense, accrued research and development expenses and other accrued liabilities, income taxes and the fair value of financial instruments. 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, 2019 September 30, 2018 Cash and cash equivalents $ 79,594 $ 142,423 Restricted cash 1,053 225 Total cash and cash equivalents and restricted cash $ 80,647 $ 142,648 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 (loss) 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 (loss). 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. A decline in the fair value below cost of available-for-sale debt securities that is deemed other-than-temporary is charged to results of operations, resulting in the establishment of a new cost basis for the security. The Company regularly evaluates whether declines in the fair value of its debt securities below their cost are other-than-temporary. The evaluation includes consideration of the cause of the impairment, including the creditworthiness of the security issuers, the number of securities in an unrealized loss position, the severity and duration of the unrealized losses, whether the Company has the intent to sell the securities and whether it is more likely than not that the Company will be required to sell the securities before the recovery of their amortized cost basis. The Company has not recorded any impairment of available-for-sale debt securities which was deemed to be to be other-than-temporary. Leases Effective January 1, 2019, the Company adopted Accounting Standards Update (ASU) 2016-02, Leases Leases Under Topic 842, the Company classifies its leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase by the Company. Lease classification is evaluated at the inception of the lease agreement. Regardless of classification, the Company records a right-of-use asset and a lease liability for all leases with a term greater than 12 months. All of the Company’s leases as of September 30, 2019 have been classified as operating leases. Operating lease expense is recognized on a straight-line basis over the term of the lease, with the exception of variable lease expenses which are recognized as incurred. The Company identifies leases in its contracts if the contract conveys the right to control the use of identified property, plant or equipment for a period of time in exchange for consideration. The Company does not allocate lease consideration between lease and nonlease components and records a lease liability equal to the present value of the remaining fixed consideration under the lease. The interest rates implicit in the Company’s leases are generally not readily determinable. Accordingly, the Company uses its estimated incremental borrowing rate at the commencement date of the lease to determine the present value discount of the lease liability. The Company estimates its incremental borrowing rate for each lease based on an evaluation of its expected credit rating and the prevailing market rates for collateralized debt in a similar economic environment with similar payment terms and maturity dates commensurate with the term of the lease. The right-of-use asset for each lease is equal to the lease liability, adjusted for unamortized initial direct costs and lease incentives and prepaid or accrued rent. Initial direct costs of entering into a lease are included in the right-of-use asset and amortized as lease expense over the term of the lease. Lease incentives, such as tenant improvements allowances, are recorded as a reduction of the right-of-use asset and amortized as a reduction of lease expense over the term of the lease. The Company excludes options to extend or terminate leases from the calculation of the lease liability unless it is reasonably certain the option will be exercised. 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. 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. Revenue Recognition The Company recognizes revenue in accordance with ASC 606, Revenue from Contracts with Customers The Company applies the five-step model to contracts that are within the scope of Topic 606 only when it is probable that the Company will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, for contracts within the scope of Topic 606, the Company assesses the goods or services promised within each contract and determine those that are performance obligations and whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to respective performance obligations when (or as) the respective performance obligations are satisfied. The Company evaluates its contracts with customers for the presence of significant financing components. If a significant financing component is identified in a contract and provides a financing benefit to the customer, the transaction price for the contract is adjusted to account for the financing portion of the arrangement, which is recognized as interest income over the financing term using the effective interest method. In determining the appropriate interest rates for significant financing components, the Company evaluates the credit profile of the customer and prevailing market interest rates and selects an interest rate in which it believes would be charged to the customer in a separate financing arrangement over a similar financing term. License and Royalty Revenue The Company licenses its NAV Technology Platform to other biotechnology and pharmaceutical companies. The terms of the licenses vary, and licenses may be exclusive or non-exclusive and may be sublicensable by the licensee. Licenses may grant intellectual property rights for purposes of internal and preclinical research and development only, or may include the rights, or options to obtain future rights, to commercialize drug therapies for specific diseases using the Company’s NAV Technology Platform. License agreements generally have a term at least equal to the life of the underlying patents, but are terminable at the option of the licensee. Consideration payable 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. The Company’s license agreements are accounted for as contracts with customers within the scope of Topic 606. At the inception of each license agreement, the Company determines the contract term for purposes of applying the requirements of Topic 606. Licenses are generally terminable at the option of the licensee with advance notice to the Company. For each license, the Company evaluates these termination rights to determine whether a substantive termination penalty would be incurred by the licensee upon termination. If the licensee incurs a substantive termination penalty upon termination, the contract term for revenue recognition purposes is generally equal to the stated term of the license, which is the life of the underlying licensed patents. Alternatively, if the licensee does not incur a substantive termination penalty upon termination, the contract term for revenue recognition purposes may be shorter than the stated term of the license, in which case the termination rights may be accounted for as contract renewal options. The determination of whether a substantive termination penalty is associated with the termination rights requires significant judgment. In making this determination, the Company considers, among other things, the nature of the intellectual property rights that would be returned to the Company upon termination, including the exclusivity of the licensed rights and the stage of development of the licensed products, the payment terms, including the amount and timing of non-refundable or guaranteed payments, and the business purpose of the termination rights granted to the licensee. Generally, the most significant judgment in determining whether a substantive termination penalty exists is the related to amount of any up-front or guaranteed non-refundable payments relative to the amount of annual payments that may be avoided by the licensee upon termination of the license. The Company considers all of the facts and circumstances relevant to each license when making this determination. Performance obligations under the Company’s license agreements may include (i) the delivery of intellectual property licenses and (ii) options granted to licensees to acquire additional licenses to the extent the options represent material rights to the licensee. At the inception of each license agreement which contains options for the licensee to acquire additional licenses, or contract renewal options, the Company evaluates the options to determine whether they provide material rights to the licensee. In making this determination, the Company considers whether the options are priced at a discount to the standalone selling price for the underlying licenses. If an option is priced at a discount to the standalone selling price for the underlying license, the option is considered to be a material right to the licensee and is accounted for as a separate performance obligation under the current license agreement. The Company evaluates the transaction price of its license agreements at the inception of each agreement and at each reporting date. The transaction price includes the fixed consideration payable to the Company during the contract term, as well as any variable consideration to the extent that it is probable that a significant reversal of revenue will not occur in the future. Fixed consideration under the license agreements includes up-front and annual fees payable during the contract term. Variable consideration under the license agreements includes development and sales-based milestone payments, sublicense fees and royalties on sales of licensed products. Consideration contingent upon the exercise of options by a licensee is excluded from the transaction price and not accounted for as part of the license agreement until the option is exercised. The transaction price for each license agreement is allocated to the underlying performance obligations and recognized as revenue when the performance obligations are satisfied. Consideration allocated to performance obligations for the delivery of an intellectual property license is recognized as revenue in full upon the delivery of the license to the licensee. Consideration allocated to performance obligations for license options is recognized as revenue in full upon the earlier of the option exercise or expiration. The exercise of a license option by a licensee is accounted for as a new license for revenue recognition purposes. Up-front and annual licenses fees payable to the Company over the contract term of each license are included in the transaction price, and the portion of this consideration that is allocated to the performance obligation for the delivery of the intellectual property license is recognized as revenue in full upon the delivery of the license to the licensee. If annual license fees are payable to the Company in periods beyond 12 months from the delivery of the license, a significant financing component is deemed to exist which provides a financing benefit to the licensee. If a significant financing component is identified, the Company adjusts the transaction price for the license to include only the present value of the annual license fees payable to the Company over the contract term. The discounted portion of the license fees is recognized as interest income from licensing over the financing period of the license. Development milestone payments are payable to the Company upon the achievement of specified development milestones by licensees. At the inception of each license agreement that contains development milestone payments, the Company evaluates whether the milestones are considered probable of achievement and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal will not occur in the future, milestone payments are included in the transaction price and recognized as revenue upon the delivery of the license. Milestone payments contingent on the achievement of development milestones that are not within the control of the Company or the licensee, such as regulatory approvals, are not considered probable of being achieved and are excluded from the transaction price until the milestone is achieved. At each reporting date, the Company re-evaluates the probability of achievement of outstanding development milestones and, if necessary, adjusts the transaction price for any milestones for which the probability of achievement has changed due to current facts and circumstances. Any such adjustments are recorded on a cumulative catch-up basis and recognized as revenue in the period of the adjustment. Royalties on sales of licensed products, sales-based milestone payments and sublicense fees based on the receipt of certain fees by licensees from any sublicensees are excluded from the transaction price of each license and recognized as revenue in the period that the related sales or sublicenses occur, provided that the associated license has been delivered to the licensee. Royalty revenue to date consists of royalties on net sales of Zolgensma®, which is marketed by AveXis, Inc. (AveXis), a wholly owned subsidiary of Novartis AG (Novartis). Zolgensma is a licensed product under the Company’s March 2014 license agreement, as amended, with AveXis for the development and commercialization of treatments for spinal muscular atrophy (SMA). The Company recognizes royalty revenue from net sales of Zolgensma in the period in which the underlying products are sold by AveXis, which in certain cases may require the Company to estimate royalty revenue for periods of net sales which have not yet been reported to the Company. Sales-based milestone payments related to net sales of Zolgensma are recognized as royalty revenue in the period in which the milestone is achieved. The Company receives payments from licensees based on the billing schedules established in each license agreement. Amounts recognized as revenue which have not yet been received from licensees, including unbilled royalties, are recorded as accounts receivable when the Company’s rights to the consideration are conditional solely upon the passage of time. Amounts recognized as revenue which have not yet been received from licensees are recorded as contract assets when the Company’s rights to the consideration are not unconditional. Contract assets are recorded as other current assets on the consolidated balance sheets. 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 consideration recorded as accounts receivable or contract assets which is not contractually payable by the licensee is charged off as a reduction of license revenue in the period of the termination. Amounts received by the Company prior to the delivery of underlying performance obligations are deferred and recognized as revenue upon the satisfaction of the performance obligations by the Company. Deferred revenue which is not expected to be recognized within 12 months from the reporting date is recorded as non-current on the consolidated balance sheets. Cost of Revenues Cost of revenues consists primarily of sublicense fees, milestone payments and royalties on net sales of licensed products as specified in the Company’s agreements with its licensors. Sublicense fees are based on a percentage of license fees received by the Company from NAV Technology Licensees and are recognized in the period that the underlying revenue is recognized. Milestone payments are payable to licensors upon the achievement of specified milestones by NAV Technology Licensees and are recognized in the period the milestone is achieved or deemed probable of achievement. Royalties are based on a percentage of net sales of licensed products by NAV Technology Licensees and are recognized in the period that the underlying sales occur. Amounts which are payable to licensors in periods beyond 12 months from the reporting date are recorded as non-current liabilities on the consolidated balance sheets. Collaborative Arrangements The Company evaluates its collaboration arrangements to determine whether they are within the scope of ASC 808, Collaborative Arrangements 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 Adoption of ASU 2016-02, Leases In February 2016, the Financial Accounting Standards Board (FASB) issued ASU 2016-02, Leases Leases The Company elected certain practical expedients allowed by Topic 842 for transition purposes, including the package of practical expedients which permitted the Company to not reassess lease identification, classification and initial direct costs under Topic 842 for leases that commenced prior to January 1, 2019. Additionally, the Company elected the practical expedient allowed for transition purposes to use hindsight in determining the terms of leases that commenced prior to January 1, 2019. Upon the adoption of Topic 842, the Company recorded operating lease right-of-use assets of $7.4 million and operating lease liabilities of $8.4 million for its leases which were in effect and had commenced prior to January 1, 2019 and had original lease terms of more than 12 months. The Company also derecognized current and non-current deferred rent liabilities of $1.4 million and prepaid expenses, other current assets and other assets of $0.4 million upon the adoption of Topic 842. Additionally, upon the adoption of Topic 842, the Company derecognized $5.9 million of property and equipment and $5.9 million of financing lease obligations related to construction-in-progress at 9800 Medical Center Drive, as the Company does not control the building during the construction period under the requirements of Topic 842. The lease term for the facility at 9800 Medical Center Drive does not commence until certain construction is completed by the landlord and the building is delivered to the Company. The right-of-use assets and lease liabilities related to the facility at 9800 Medical Center Drive will not be recognized on the Company’s consolidated balance sheets until the commencement date of the lease, which is expected to occur in 2020. The cumulative impact of the adoption of Topic 842 resulted in an increase in accumulated deficit of less than $0.1 million on January 1, 2019. The adoption of Topic 842 did not have a material impact on the Company’s results of operations for the three and nine months ended September 30, 2019, nor does the Company believe it will have a material impact on future results of operations based on its current leasing arrangements. Other Recently Adopted Accounting Pronouncements In November 2018, the FASB issued ASU 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction Between Topic 808 and Topic 606 In February 2018, the FASB issued ASU 2018-02, Income Statement—Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income Tax Cuts and Jobs Act of 2017 (the TCJA) In April 2017, the FASB issued ASU 2017-08, Receivables—Nonrefundable Fees and Other Costs (Subtopic 310-20) Recent Accounting Pronouncements Not Yet Adopted 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 August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement measurements. The standard is effective for the Company beginning January 1, 2020, with early adoption permitted upon issuance. The Company does not believe the application of this standard will have a material impact on its financial statement disclosures. In June 2016, the FASB issued ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments

Marketable Securities

Marketable Securities	9 Months Ended
	Sep. 30, 2019
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 Unrealized Gains Unrealized Losses Fair Value September 30, 2019 U.S. government and federal agency securities $ 78,093 $ 296 $ (3 ) $ 78,386 Certificates of deposit 7,529 87 — 7,616 Corporate bonds 220,694 1,018 (21 ) 221,691 Equity securities 420 29,420 — 29,840 $ 306,736 $ 30,821 $ (24 ) $ 337,533 Amortized Cost Unrealized Gains Unrealized Losses Fair Value December 31, 2018 U.S. government and federal agency securities $ 103,410 $ 93 $ (37 ) $ 103,466 Certificates of deposit 8,992 — — 8,992 Corporate bonds 282,902 36 (377 ) 282,561 $ 395,304 $ 129 $ (414 ) $ 395,019 As of September 30, 2019 and December 31, 2018, 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, 2019 and December 31, 2018, the balance in the Company’s accumulated other comprehensive income (loss) 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, 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 periods. 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 (loss) during the periods and were included in investment income in the consolidated statements of operations and comprehensive income (loss). During the three and nine months ended September 30, 2018, the Company recognized net unrealized losses on available-for-sale debt securities of $0.1 million and $0.2 million, respectively, and income tax expense of zero in other comprehensive income (loss) for the periods. The Company recognized net realized losses 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, 2018, which were reclassified out of accumulated other comprehensive income (loss) during the periods and were included in investment income in the consolidated statements of operations and comprehensive income (loss). Realized gains and losses from the sale or maturity of available-for-sale debt securities are determined based on the specific identification method. 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, 2019 U.S. government and federal agency securities $ 4,497 $ (3 ) $ — $ — $ 4,497 $ (3 ) Corporate bonds 23,354 (21 ) — — 23,354 (21 ) $ 27,851 $ (24 ) $ — $ — $ 27,851 $ (24 ) Less than 12 Months 12 Months or Greater Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses December 31, 2018 U.S. government and federal agency securities $ 53,124 $ (37 ) $ — $ — $ 53,124 $ (37 ) Corporate bonds 245,283 (354 ) 12,424 (23 ) 257,707 (377 ) $ 298,407 $ (391 ) $ 12,424 $ (23 ) $ 310,831 $ (414 ) As of September 30, 2019, available-for-sale debt securities held by the Company which were in an unrealized loss position consisted of 7 investment grade security positions. The Company has the intent and ability to hold such securities until recovery and has determined that none of its available-for-sale debt securities were other-than-temporarily impaired as of September 30, 2019 or December 31, 2018. Marketable equity securities held by the Company as of September 30, 2019 consisted 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. The Company recognized unrealized gains (losses) of $(2.2) million and $29.4 million during the three and nine months ended September 30, 2019, respectively, related to the marketable equity securities of Prevail, which are included in investment income in the consolidated statements of operations and comprehensive income (loss). Pursuant to a lock-up agreement executed in connection with Prevail’s IPO, the Company is restricted from selling its common stock of Prevail prior to December 2019. As of September 30, 2019, no amounts have been realized by the Company related to its marketable securities of Prevail as there have been no sales of the securities.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	9 Months Ended
	Sep. 30, 2019
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, 2019 Cash equivalents: Money market mutual funds $ — $ 72,634 $ — $ 72,634 Corporate bonds — 5,905 — 5,905 Total cash equivalents — 78,539 — 78,539 Marketable securities: U.S. government and federal agency securities — 78,386 — 78,386 Certificates of deposit — 7,616 — 7,616 Corporate bonds — 221,691 — 221,691 Equity securities 29,840 — — 29,840 Total marketable securities 29,840 307,693 — 337,533 Total cash equivalents and marketable securities $ 29,840 $ 386,232 $ — $ 416,072 Quoted Significant prices other Significant in active observable unobservable markets inputs inputs (Level 1) (Level 2) (Level 3) Total December 31, 2018 Cash equivalents: Money market mutual funds $ — $ 75,542 $ — $ 75,542 Total cash equivalents — 75,542 — 75,542 Marketable securities: U.S. government and federal agency securities — 103,466 — 103,466 Certificates of deposit — 8,992 — 8,992 Corporate bonds — 282,561 — 282,561 Total marketable securities — 395,019 — 395,019 Total cash equivalents and marketable securities $ — $ 470,561 $ — $ 470,561 There were no transfers of financial instruments between levels of the fair value hierarchy during the nine months ended September 30, 2019. 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, 2019 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 December 31, 2018, non-marketable equity securities had a carrying value of $0.4 million and were included in other assets on the consolidated balance sheets. The Company did not identify any observable price changes or changes in circumstances that would have had an adverse effect on the fair value of the securities as of December 31, 2018. During the nine months ended September 30, 2019, all of the Company’s non-marketable equity securities were reclassified to marketable securities and as of September 30, 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, 2019 and 2018.

Property and Equipment, Net

Property and Equipment, Net	9 Months Ended
	Sep. 30, 2019
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, 2019 December 31, 2018 Lab equipment $ 18,492 $ 14,417 Computer equipment and software 2,448 2,002 Furniture and fixtures 1,960 1,915 Leasehold improvements 17,831 11,751 Construction-in-progress — 5,854 Total property and equipment 40,731 35,939 Accumulated depreciation and amortization (12,444 ) (7,237 ) Property and equipment, net $ 28,287 $ 28,702 Construction-in-progress reported in the table above as of December 31, 2018 consisted of certain costs incurred and reported by the Company’s landlord at 9800 Medical Center Drive. Upon the adoption of Topic 842 on January 1, 2019, the Company derecognized the cumulative amount of construction costs incurred by the landlord of $5.9 million. Please refer to Note 2 for further information on the Company’s adoption of Topic 842 and Note 6 for further information on the Company’s lease at 9800 Medical Center Drive.

Leases

Leases	9 Months Ended
	Sep. 30, 2019
Leases [Abstract]
Leases	6. Leases 9800 Medical Center Drive In November 2018, the Company entered into a lease agreement, as amended in April 2019, for approximately 139,000 square feet of office and laboratory facilities in a new building to be constructed at 9800 Medical Center Drive in Rockville, Maryland (the 9800 Medical Center Drive Lease). The initial construction of the building is being conducted by the landlord and is expected to be completed in 2020, after which the leased premises will be delivered to the Company to make additional improvements to the building. Pursuant to the amended lease agreement, the Company will receive a $15.3 million tenant improvement allowance from the landlord to construct additional improvements to the leased premises. The lease expires approximately 16 years from delivery of the leased premises to the Company, subject to certain extension and termination options held by the Company. 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 after 12 years from the delivery of the leased premises to the Company. If the Company elects to terminate the lease, it will be subject to a termination fee equal to the unamortized tenant improvement allowance, rent abatement and landlord commissions as of the termination date, bearing interest at 5% per annum, plus four months of base rent and operating expenses. Additionally, after the delivery of the leased premises under the 9800 Medical Center Drive Lease, the Company will have the option to terminate its lease at 9712 Medical Center Drive with six months’ notice. Monthly payments under the 9800 Medical Center Drive Lease begin approximately 12 months from the delivery of the leased premises to the Company and escalate annually in accordance with the lease agreement. As required by the lease agreement, the Company has provided the landlord with an irrevocable letter of credit of $0.8 million which the landlord may draw upon in the event of any uncured default by the Company under the terms of the lease. The Company is involved in the construction project for the leased premises at 9800 Medical Center Drive, including having the responsibility to pay for a portion of the costs of non-normal tenant improvements such as finish work, mechanical, electrical and plumbing elements of the building, among other items. As of December 31, 2018, under the requirements of Topic 840, the Company was deemed the owner of the leased premises during the construction period for accounting purposes and certain estimated construction costs incurred and reported by the landlord were recorded as property and equipment, with a corresponding financing lease obligation, on the consolidated balance sheet. The Company has determined that it does not control the building during the construction period under the requirements of Topic 842. Accordingly, upon the adoption of Topic 842 on January 1, 2019, the Company derecognized property and equipment of $5.9 million for the cumulative costs of construction incurred by the landlord as well as the associated $5.9 million financing lease obligation. As of September 30, 2019, the Company had recorded $5.4 million of costs related to construction-in-progress at 9800 Medical Center Drive, which have been recorded as leasehold improvements within property and equipment on the consolidated balance sheets. As of September 30, 2019, the right-of-use assets and lease liabilities related to the 9800 Medical Center Drive Lease have not been recorded on the Company’s consolidated balance sheets and will be measured and recognized on the commencement date of the lease, which is expected to occur in 2020 when the landlord delivers the newly constructed building to the Company. In November 2019, the Company amended the 9800 Medical Center Drive Lease to expand the leased premises to include the entire rentable square footage of the building (the November 2019 Amendment). The November 2019 Amendment increased the leased square footage by approximately 38,000 square feet, expanding the total leased premises from approximately 139,000 square feet to approximately 177,000 square feet. Total additional lease payments related to the November 2019 Amendment are estimated to be $22.6 million over the lease term, which are subject to adjustment based on the actual square footage of the facility once constructed. Additionally, the November 2019 Amendment resulted in an increase in the Company’s tenant improvement allowance from $15.3 million to $19.5 million. Other Leases 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 has options to extend the term of the 9712 Medical Center Drive Lease for up to six additional years. Additionally, upon the commencement of the 9800 Medical Center Drive Lease, the Company will have 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 have been excluded from the measurement of the right-of-use assets and lease liabilities for the lease as they are 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 rent expense over the term of the lease. 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. In November 2017, the Blackwell Road Lease was amended to include additional office space for the remainder of the lease term. Monthly payments under the lease began in September 2016 and escalate annually in accordance with the lease agreement. The Company has an option to extend the term of the Blackwell Road Lease for up to five additional years and the option to terminate the lease after 67 months from the lease commencement date. If the Company elects to terminate the lease, it will be subject to a termination fee equal to the unamortized tenant improvement allowance, rent abatement and landlord costs and commissions as of the termination date, bearing interest at 8% per annum. The Company’s extension and termination options under the Blackwell Road Lease have been excluded from the measurement of the right-of-use assets and lease liabilities for the lease as they are not reasonably certain of exercise. The Company received a $0.8 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 rent expense over the term of the lease. 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. 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. In May 2019, the 400 Madison Lease was amended to include additional office space and extend the term of the lease. Prior to the amendment, the lease was to expire in October 2020. Pursuant to the amendment, the Company vacated the original leased premises during the third quarter of 2019, upon which the landlord began the demolition of the original premises as well as the additional premises under the amended lease. Upon completion of the demolition, the landlord will deliver the entire expanded premises to the Company to make tenant improvements. The amended lease will expire approximately 7.5 years from the date the expanded premises are delivered to the Company, which occurred in October 2019. The Company will receive a $0.7 million tenant improvement allowance from the landlord to construct improvements to the leased premises. As a result of the amendment in May 2019, the expiration of the lease term for the original premises under the 400 Madison Lease was adjusted from October 2020 to August 2019. Accordingly, upon the execution of the amendment in May 2019, the right-of-use assets and lease liabilities for the original premises were reduced by $0.4 million to account for the modification of the lease term. As of September 30, 2019, the Company did not have control of the original or additional leased premises under the amended lease and no right-of-use assets and lease liabilities under the 400 Madison Lease were recorded on the Company’s consolidated balance sheets. The right-of-use assets and lease liabilities related to the expanded premises for the extended lease term will be measured and recognized upon the delivery of the expanded premises to the Company to make tenant improvements , which occurred in October 2019. The Company leases additional office and laboratory facilities in Rockville, Maryland, as well as laboratory and other equipment, under operating leases with various expiration dates through 2022. 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, 2019 September 30, 2019 Operating lease cost $ 690 $ 2,088 Variable lease cost 164 463 Total lease cost $ 854 $ 2,551 Cash paid for amounts included in operating lease liabilities $ 757 $ 2,152 Right-of-use assets acquired through operating lease liabilities $ 557 $ 222 Right-of-use assets acquired through operating lease liabilities for the nine months ended September 30, 2019 includes a reduction of $0.4 million related to the May 2019 amendment to the 400 Madison Lease for the adjustment of the lease term. Short-term lease expense for the three and nine months ended September 30, 2019 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, 2019 Weighted-average remaining lease term (years) 2.7 Weighted-average discount rate 5.5 % The following table presents a reconciliation of the undiscounted future minimum lease payments remaining under leases that have not yet commenced and other operating leases to the amounts reported as operating lease liabilities on the consolidated balance sheet as of September 30, 2019 (in thousands): Leases Other Total Not Yet Operating Minimum Lease Commenced (a) Leases Payments Undiscounted future minimum lease payments: 2019 (remainder of year) $ 73 $ 521 $ 594 2020 413 3,057 3,470 2021 2,306 2,662 4,968 2022 5,420 631 6,051 2023 6,369 479 6,848 Thereafter 83,731 — 83,731 Total undiscounted future minimum lease payments $ 98,312 $ 7,350 $ 105,662 Amount representing imputed interest (524 ) Total operating lease liabilities 6,826 Current portion of operating lease liabilities (2,506 ) Operating lease liabilities, non-current $ 4,320 (a) Includes undiscounted future minimum lease payments under the 9800 Medical Center Drive Lease and 400 Madison Lease which are not included in the lease liabilities reported on the consolidated balance sheet as of September 30, 2019. The actual timing and amounts of these payments are subject to adjustment based on the commencement dates and actual square footage of the leased premises. Accordingly, these amounts were estimates as of September 30 , 2019. As of December 31, 2018, future minimum lease payments under Topic 840 for the 9800 Medical Center Drive Lease and other operating leases were as follows (in thousands): 9800 Medical Other Total Center Drive Operating Minimum Lease Lease (a) Leases Payments 2019 $ — $ 2,798 $ 2,798 2020 — 3,054 3,054 2021 1,329 2,391 3,720 2022 4,289 621 4,910 2023 5,156 479 5,635 Thereafter 76,420 — 76,420 Total minimum lease payments $ 87,194 $ 9,343 $ 96,537 (a) Includes all future minimum lease payments under the 9800 Medical Center Drive Lease, including amounts recorded as financing lease obligations on the consolidated balance sheet . The actual timing and amounts of payments under the 9800 Medical Center Drive Lease are subject to adjustment based on the commencement date and actual square footage of the leased premises. Accordingly, these amounts were estimates as of December 31, 2018.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2019
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	7. Commitments and Contingencies Licenses and Collaborations The Trustees of the University of Pennsylvania In February 2009, the Company entered into a license agreement, which has been amended from time to time, with The Trustees of the University of Pennsylvania (together with the University of Pennsylvania, Penn) for exclusive, worldwide rights to certain patents owned by Penn underlying the Company’s NAV Technology Platform, as well as exclusive rights to certain data, results and other information generated in connection with the clinical trial for RGX-501, the Company’s product candidate for the treatment of homozygous familial hypercholesterolemia (HoFH). Pursuant to the license agreement, the Company and is obligated to pay Penn royalties on net sales of licensed products and sublicense fees. Additionally, the Company is obligated to reimburse Penn for certain costs incurred related to the maintenance of the licensed patents. In April 2019, the Company amended its license from Penn to include exclusive license rights to certain know-how, including research data and other information, relating to the treatment of late-infantile neuronal ceroid lipofuscinosis type 2 (CLN2) disease. In consideration for the additional licensed rights, and in addition to any consideration owed under the license prior to the amendment, the Company paid Penn an up-front fee and is obligated to pay milestone fees of up to $20.5 million upon the achievement of various development and sales-based milestones and additional royalties on net sales of licensed products for the treatment of CLN2 disease. Additionally, the amendment modifies the percentage of sublicense fees the Company is obligated to pay Penn on amounts the Company receives from third parties for the sublicensing of the licensed rights for the treatment of CLN2 disease. Neurimmune AG In July 2019, the Company entered into a collaboration and license agreement with Neurimmune AG (Neurimmune) pursuant to which the Company and Neurimmune will jointly develop and commercialize novel gene therapies using AAV vectors from the NAV Technology Platform to deliver human antibodies for chronic neurodegenerative diseases. The Company and Neurimmune will share all research and development costs for the first two years of the agreement, after which each party will have the option, on a target-by-target basis, to: (i) continue as a 50% partner in the collaboration; (ii) receive a phase-based worldwide royalty in lieu of continued development investment; or (iii) negotiate with the other party to lead the development and commercialization of the respective program. Unless the parties agree otherwise, upon the commercialization of any product candidates, if any, it is anticipated that profits and losses will be shared equally on a worldwide basis. The Company evaluated the collaboration and license agreement with Neurimmune and determined that it is a collaborative arrangement within the scope of Topic 808, and that no unit of account under the arrangement should be accounted for as a transaction with a customer within the scope of Topic 606. In accordance with the Company’s accounting policies for collaborative arrangements, if Neurimmune’s development costs incurred under the collaboration exceed those incurred by the Company during a reporting period, the Company will recognize research and development expense and record a liability for the amount due to Neurimmune at the end of the period. Alternatively, if the Company’s development costs incurred under the collaboration exceed those incurred by the Neurimmune during a reporting period, the Company will recognize a reduction of research and development expense s and record an amount due from Neurimmune at the end of the period. During the three and nine months ended September 30, 2019, the Company recognized net research and development expenses of less than $ 0.1 million under the collaboration and license agreement with Neurimmune. Clearside Biomedical, Inc. In August 2019, the Company entered into an option and license agreement with Clearside Biomedical, Inc. (Clearside) pursuant to which the Company was granted an option to exclusively license the worldwide rights to certain patents related to Clearside’s proprietary, in-office SCS Microinjector™ for the delivery of RGX-314 to the suprachoroidal space to treat wet age-related macular degeneration (wet AMD), diabetic neuropathy (DR) and other diseases. The Company exercised its license option in October 2019, resulting in a payment of $1.6 million to Clearside upon exercise. Additionally, the Company is obligated to pay milestone fees of up to $136.0 million upon the achievement of various development and sales-based milestones, as well as royalties on net sales of licensed products using the SCS Microinjector. Clearside is responsible for supplying the SCS Microinjector to the Company to support all preclinical, clinical and commercial needs. European Patent Office Proceeding In June 2017, a third party filed an opposition with the European Patent Office (EPO) challenging the validity of a European patent owned by Penn for the AAV8 vector, which the Company has exclusively licensed (EU AAV8 Patent). The EPO conducted oral proceedings in October 2018 and upheld the validity of the EU AAV8 Patent subject to certain amendments made during the proceeding. Each party to the proceeding has appealed the EPO’s ruling. As of September 30, 2019 and December 31, 2018, the Company had not recorded any liabilities related to this matter nor does the Company believe this matter will have a material adverse impact on its business.

License and Royalty Revenue

License and Royalty Revenue	9 Months Ended
	Sep. 30, 2019
License Agreement Revenue Recognition [Abstract]
License and Royalty Revenue	8. License and Royalty Revenue As of September 30, 2019, 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 only included in the transaction price of each license and recognized as license revenue to the extent they 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, 2019, 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 $20.1 million upon the commencement of various stages of clinical trials, $31.0 million upon the submission of regulatory approval filings, $96.0 million upon the approval of commercial products by regulatory agencies and $207.0 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. The following tables present changes in the balances of the Company’s receivables, contract assets and contract liabilities during the periods presented (in thousands): Balance at Beginning Net Additions Balance at of Period (Deductions) End of Period Three Months Ended September 30, 2019 Receivables and contract assets: Accounts receivable, current and non-current $ 33,634 $ 9,886 $ 43,520 Contract assets $ — $ — $ — Contract liabilities: Deferred revenue, current and non-current $ 3,333 $ — $ 3,333 Balance at Beginning Net Additions Balance at of Period (Deductions) End of Period Nine Months Ended September 30, 2019 Receivables and contract assets: Accounts receivable, current and non-current $ 31,599 $ 11,921 $ 43,520 Contract assets $ 750 $ (750 ) $ — Contract liabilities: Deferred revenue, current and non-current $ 3,933 $ (600 ) $ 3,333 Balance at Beginning Net Additions Balance at of Period (Deductions) End of Period Three Months Ended September 30, 2018 Receivables and contract assets: Accounts receivable, current and non-current $ 5,224 $ 2,002 $ 7,226 Contract assets $ — $ 2,000 $ 2,000 Contract liabilities: Deferred revenue, current and non-current $ 600 $ — $ 600 Balance at Beginning Net Additions Balance at of Period (Deductions) End of Period Nine Months Ended September 30, 2018 Receivables and contract assets: Accounts receivable, current and non-current $ 5,850 $ 1,376 $ 7,226 Contract assets $ 350 $ 1,650 $ 2,000 Contract liabilities: Deferred revenue, current and non-current $ — $ 600 $ 600 The net increases in accounts receivable during the three and nine months ended September 30, 2019 were primarily attributable to royalties on net sales of Zolgensma, which commenced in the second quarter of 2019. During the three and nine months ended September 2019, the Company recognized royalty revenue of $9.2 million and $10.1 million, respectively, related to net sales of Zolgensma. As of September 30, 2019, the Company had recorded accounts receivable of $9.2 million related to Zolgensma royalties. As of September 30, 2019, the Company had recorded deferred revenue, current and non-current, of $3.3 million which represents consideration received from licensees for performance obligations that have not yet been satisfied by the Company. Unsatisfied performance obligations consist of options granted to licensees that provide material rights to the licensee to acquire additional licenses from the Company. These performance obligations will be satisfied, and underlying revenue will be recognized, upon the exercise or expiration of the options. During the three and nine months ended September 30, 2019, the Company recognized zero million and $0.6 million, respectively, of license revenue that was included in deferred revenue at the beginning of the period as a result of options exercised by licensees during the period. The Company did not recognize any license revenue during the three and nine months ended September 30, 2018 that was included in deferred revenue at the beginning of the period. During the three and nine months ended September 30, 2019, the Company recognized license revenue of $0.9 million and $4.6 million, respectively, from licenses delivered to licensees in prior periods as a result of changes in the transaction prices of its license agreements. Changes in the transaction prices during the three and nine months ended September 30, 2019 were primarily attributable to development milestones achieved or deemed probable of achievement during the period that were previously not considered probable of achievement. During the three and nine months ended September 30, 2018, the Company recognized license revenue of $4.1 million and $4.2 million, respectively, from licenses delivered to licensees in prior periods as a result of changes in the transaction prices of its license agreements. Changes in the transaction prices during the three and nine months ended September 30, 2018 were primarily attributable to development milestones achieved or deemed probable of achievement during the period that were previously not considered probable of achievement . Changes in the transaction price exclude revenue recognized from sublicense fees and royalties on sales of licensed products, which are excluded from the transaction price and recognized as revenue in the period that the underlying sales or sublicenses occur. As of September 30, 2019, the Company had recorded total current and non-current accounts receivable of $43.5 million, of which $1.2 million had been billed to customers and $42.4 million was billable to customers in future periods. As of December 31, 2018, the Company had recorded total current and non-current accounts receivable of $31.6 million, of which $0.4 million had been billed to customers and $31.2 million was billable to customers in future periods. Accounts receivable, current and non-current, as of September 30, 2019 and December 31, 2018 included $28.0 million and $26.0 million, respectively, related to the November 2018 license agreement with Abeona Therapeutics Inc. for the development and commercialization of treatments for various diseases. The Company believes that it is not exposed to significant credit risk related to accounts receivable due to the credit quality and history of collections from its significant customers. The Company is unaware of any concentrations of credit risk related to accounts receivable from significant customers with deteriorated credit quality. As of September 30, 2019 and December 31, 2018, the Company had not recognized any impairment losses on its receivables or contract assets from contracts with customers and no allowance for doubtful accounts was recorded. AveXis March 2014 License and January 2018 Amendment In March 2014, the Company entered into an exclusive license agreement (the March 2014 License) with AveXis. Under the license, the Company granted AveXis an exclusive, worldwide commercial license, with rights to sublicense, to the NAV AAV9 vector for the treatment of SMA in humans by in vivo gene therapy. mid-single to low double-digit royalties on net sales of licensed products, I n January 2018, the Company and AveXis amended the March 2014 License (the January 2018 Amendment). Under the January 2018 Amendment, the licensed intellectual property was expanded to include, in addition to the NAV AAV9 vector previously licensed, sublicenses to other third-party patents exclusively licensed by the Company as well as any other recombinant AAV vector in the Company’s intellectual property portfolio during a period of 14 years from the effective date of the January 2018 Amendment, for the treatment of SMA in humans by in vivo gene therapy. The Company may also, in its sole discretion, provide specified collaborative services to AveXis as specified in the January 2018 Amendment. The January 2018 Amendment also modified the assignment provision of the March 2014 License. Under the amended assignment provision, AveXis was permitted to transfer the March 2014 License, as amended, without the Company’s consent in connection with a change of control of AveXis, subject to certain conditions. Under the original March 2014 License, any assignment by AveXis without the Company’s prior written consent had been prohibited. In consideration for the additional rights granted under the January 2018 Amendment, and in addition to any consideration owed under the original March 2014 License, AveXis paid to the Company a fee of $80.0 million upon entry into the January 2018 Amendment. In addition, AveXis was obligated to pay the Company (i) $30.0 million on the first anniversary of the effective date of the January 2018 Amendment, (ii) $30.0 million on the second anniversary of the effective date of the January 2018 Amendment and (iii) potential sales-based milestone payments of up to $120.0 million. In the event of a change of control of AveXis, to the extent that any fee described in (i) or (ii) above, or the first $40.0 million of sales-based milestone payments described in (iii) above, had not yet been paid to the Company, AveXis was required to pay any such unpaid fee to the Company upon the change of control. For any product developed for the treatment of SMA using the NAV AAV9 vector, AveXis will continue to be obligated to pay to the Company mid-single to low double-digit royalties on net sales as required by the March 2014 License, and for any product developed for the treatment of SMA using a licensed vector other than NAV AAV9, the Company will receive a low double-digit royalty on net sales. In May 2018, AveXis was acquired by Novartis, which qualified as a change of control of AveXis under the January 2018 Amendment. Pursuant to the January 2018 Amendment, AveXis paid the Company $100.0 million in accelerated license payments as a result of the change of control. In May 2019, the U.S. Food and Drug Administration (the FDA) approved Zolgensma for marketing in the United States, which is a licensed product under the March 2014 License, as amended, with AveXis. Upon its commercial launch in the second quarter of 2019, the Company began recognizing royalty revenue on net sales of Zolgensma. Accounting Analysis The January 2018 Amendment was accounted for under Topic 606 as a modification of the license agreement resulting in a new and separate contract from the original March 2014 License for revenue recognition purposes. The Company determined that a substantive termination penalty is associated with AveXis’ termination rights under the amended license agreement, and therefore the contract term for revenue recognition purposes is equal to the stated term of the license. The only material performance obligation of the Company under the January 2018 Amendment is for the delivery of the modified license, which occurred upon the execution of the amendment in January 2018. As of September 30, 2019, the transaction price of the original March 2014 License was $11.0 million. The transaction price includes (i) the up-front payment in March 2014 of $2.0 million, (ii) the present value of aggregate annual fees payable to the Company over the term of the license and (iii) payments for development milestones achieved to date or which are deemed probable of achievement. The discounted portion of the annual fees represents the financing benefit provided to AveXis and is recognized as interest income from licensing over the term of the license. Variable consideration under the original March 2014 License, which has been excluded from the transaction price, includes $3.5 million in payments for remaining development milestones that had not yet been achieved and were not considered probable of achievement, as well as any potential sublicense fees or royalties on sales of licensed products, which will be recognized in the period of the underlying sales or sublicenses. The transaction price of the original March 2014 License increased by $3.5 million during the nine months ended September 30, 2019 as a result of development milestones achieved during the period which were previously excluded from the transaction price. Upon its execution, the transaction price of the January 2018 Amendment was $132.1 million, which was fully recognized as license revenue upon the delivery of the modified license in January 2018. In May 2018, as a result of the acquisition of AveXis by Novartis, the transaction price was increased by $40.0 million to account for the acceleration of the sale-based milestone which was previously excluded from the transaction price. The $40.0 million increase in the transaction price was recognized as license revenue upon the completion of the change of control in May 2018 since the amended license had been fully delivered to AveXis. Additionally, due to the acceleration of the two $30.0 million payments originally due in January 2019 and January 2020, the Company recognized $6.1 million of interest income from licensing upon the completion of the change of control of AveXis, which represents the remaining present value discount on such payments as of the date of the change of control. As of September 30, 2019, the transaction price of the January 2018 Amendment was $172.1 million, which includes: (i) the $80.0 million payment in January 2018, (ii) the present value, as of the date of the January 2018 Amendment, of the two $30.0 million payments originally due in January 2019 and January 2020 and (iii) the $40.0 million sales-based milestone which was accelerated upon the change of control in May 2018. Variable consideration under the January 2018 Amendment, which has been excluded from the transaction price, includes the remaining sales-based milestone payment of $80.0 million, as well as any potential sublicense fees or royalties on sales of licensed products, which will be recognized in the period of the underlying sales or sublicenses . There were no increases in the transaction price of the January 2018 Amendment during the nine months ended September 30, 2019. The Company recognized the following amounts under the March 2014 License with AveXis, as amended, which include amounts from both the original March 2014 License and the January 2018 Amendment (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 License revenue $ — $ 4,000 $ 3,500 $ 176,066 Zolgensma royalty revenue 9,182 — 10,106 — Total license and royalty revenue $ 9,182 $ 4,000 $ 13,606 $ 176,066 Interest income from licensing $ 7 $ 8 $ 22 $ 7,958 As of September 30, 2019, the Company had recorded $9.4 million of accounts receivable from AveXis under the March 2014 License, as amended, of which $9.2 million were included in current assets and $0.2 million were included in non-current assets. As of December 31, 2018, the Company had recorded $0.2 million of accounts receivable from AveXis under the March 2014 License, as amended, of which less than $0.1 million were included in current assets and $0.2 million were included in non-current assets.

Stock-based Compensation

Stock-based Compensation	9 Months Ended
	Sep. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-based Compensation	9. Stock-based Compensation In January 2019, an additional 1,444,808 shares became available for issuance under the 2015 Equity Incentive Plan (the 2015 Plan). As of September 30, 2019, the total number of shares of common stock authorized for issuance under the 2015 Plan and the 2014 Stock Plan (the 2014 Plan) was 10,933,221, of which 2,189,562 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, 2019 2018 2019 2018 Stock options $ 6,965 $ 4,309 $ 19,261 $ 11,248 Restricted stock units 69 69 206 206 Employee stock purchase plan 128 105 512 301 $ 7,162 $ 4,483 $ 19,979 $ 11,755 As of September 30, 2019, the Company had $67.7 million of unrecognized stock-based compensation expense related to stock options, restricted stock units and the 2015 Employee Stock Purchase Plan (the 2015 ESPP), which is expected to be recognized over a weighted-average period of 2.8 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, 2019 2018 2019 2018 Research and development $ 3,657 $ 1,940 $ 9,530 $ 5,364 General and administrative 3,505 2,543 10,449 6,391 $ 7,162 $ 4,483 $ 19,979 $ 11,755 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, 2018 4,855 $ 19.31 7.6 $ 118,185 Granted 1,596 $ 47.82 Exercised (684 ) $ 8.07 Cancelled or forfeited (237 ) $ 33.74 Outstanding at September 30, 2019 5,530 $ 28.31 7.7 $ 69,769 Exercisable at September 30, 2019 2,827 $ 15.48 6.6 $ 60,340 Vested and expected to vest at September 30, 2019 5,530 $ 28.31 7.7 $ 69,769 (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, 2019 was $31.84. During the nine months ended September 30, 2019, the total number of stock options exercised was 684,218, resulting in total proceeds of $5.5 million. The total intrinsic value of options exercised during the nine months ended September 30, 2019 was $27.8 million. Restricted Stock Units The following table summarizes restricted stock unit activity under the 2015 Plan (in thousands, except per share data): Weighted- average Grant Date Shares Fair Value Unvested balance at December 31, 2018 40 $ 20.90 Granted — $ — Vested — $ — Forfeited — $ — Unvested balance at September 30, 2019 40 $ 20.90 Employee Stock Purchase Plan As of September 30, 2019, the total number of shares of common stock authorized for issuance under the 2015 ESPP was 254,000, of which 133,586 remained available for future issuance. During the nine months ended September 30, 2019, 35,994 shares of common stock were issued under the 2015 ESPP.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Income Taxes	10. 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 a three-year cumulative loss position as of September 30, 2019 and December 31, 2018, the Company has concluded that it is more likely than not that the benefit of its deferred tax assets will not be realized. Accordingly, the Company has provided a full valuation allowance for its net deferred tax assets as of September 30, 2019 and December 31, 2018. During the three and nine months ended September 30, 2019, the Company recognized income tax benefit of $0.2 million and $0.4 million, respectively, and income tax benefit (expense) in other comprehensive income (loss) of less than $0.1 million and $(0.6) million, respectively, related to net unrealized gains on available-for-sale debt securities. As of September 30, 2019, the Company had accrued $0.3 million related to this tax benefit, which is expected to be generated from losses in continuing operations in 2019 and is included in accrued expenses and other current liabilities on the consolidated balance sheet.

Related Party Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 2019
Related Party Transactions [Abstract]
Related Party Transactions	11. 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 services provided and increase the monthly fee, and the amended agreement expires in December 2020. 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 for the three and nine months ended September 30, 2018 were $0.5 million and $1.6 million, respectively. Expenses incurred under the agreements with FOXKISER are recorded as research and development expenses in the consolidated statements of operations and comprehensive income (loss).

Net Income (Loss) Per Share

Net Income (Loss) Per Share	9 Months Ended
	Sep. 30, 2019
Earnings Per Share [Abstract]
Net Income (Loss) Per Share	12. Net Income (Loss) Per Share The computations of basic and diluted net income (loss) per share are as follows (in thousands, except per share data): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Basic net income (loss) per share: Net income (loss) applicable to common stockholders $ (34,584 ) $ (19,202 ) $ (68,269 ) $ 95,631 Shares used in computation: Weighted-average common shares outstanding 36,813 33,988 36,618 32,576 Basic net income (loss) per share $ (0.94 ) $ (0.56 ) $ (1.86 ) $ 2.94 Diluted net income (loss) per share: Net income (loss) applicable to common stockholders $ (34,584 ) $ (19,202 ) $ (68,269 ) $ 95,631 Shares used in computation: Weighted-average common shares outstanding 36,813 33,988 36,618 32,576 Stock options — — — 3,268 Restricted stock units — — — 31 Weighted-average diluted common shares 36,813 33,988 36,618 35,875 Diluted net income (loss) per share $ (0.94 ) $ (0.56 ) $ (1.86 ) $ 2.67 For periods in which the Company incurred net losses applicable to common stockholders, common stock equivalents are excluded from the calculation of diluted net loss per share as their effect would be anti-dilutive, and accordingly, basic and diluted net loss per share are the same for such periods. Outstanding stock options with exercise prices greater than the average market price of common stock are excluded from the calculation of diluted net income (loss) per share as their effect would be anti-dilutive. 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, 2019 2018 2019 2018 Stock options issued and outstanding 5,530 5,171 5,530 1,128 Unvested restricted stock units outstanding 40 40 40 — Employee stock purchase plan 16 4 16 4 5,586 5,215 5,586 1,132

Supplemental Disclosures

Supplemental Disclosures	9 Months Ended
	Sep. 30, 2019
Payables And Accruals [Abstract]
Supplemental Disclosures	13. Supplemental Disclosures Accrued expenses and other current liabilities consists of the following (in thousands): September 30, 2019 December 31, 2018 Accrued personnel costs $ 8,869 $ 9,484 Accrued external research and development expenses 4,390 4,274 Accrued sublicense fees and royalties 3,245 1,617 Accrued external general and administrative expenses 1,137 773 Accrued income taxes payable 508 726 Accrued purchases of property and equipment 349 221 Other accrued expenses and current liabilities 733 69 $ 19,231 $ 17,164 Other liabilities of $1.8 million and $2.5 million reported as of September 30, 2019 and December 31, 2018, respectively, consist of accrued sublicense fees payable to licensors in periods beyond 12 months from the reporting date.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2019
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, 2018 included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018, which was filed with the SEC on February 27, 2019. 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, 2018, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018. 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, stock-based compensation expense, accrued research and development expenses and other accrued liabilities, income taxes and the fair value of financial instruments.
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, 2019 September 30, 2018 Cash and cash equivalents $ 79,594 $ 142,423 Restricted cash 1,053 225 Total cash and cash equivalents and restricted cash $ 80,647 $ 142,648
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 (loss) 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 (loss). 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. A decline in the fair value below cost of available-for-sale debt securities that is deemed other-than-temporary is charged to results of operations, resulting in the establishment of a new cost basis for the security. The Company regularly evaluates whether declines in the fair value of its debt securities below their cost are other-than-temporary. The evaluation includes consideration of the cause of the impairment, including the creditworthiness of the security issuers, the number of securities in an unrealized loss position, the severity and duration of the unrealized losses, whether the Company has the intent to sell the securities and whether it is more likely than not that the Company will be required to sell the securities before the recovery of their amortized cost basis. The Company has not recorded any impairment of available-for-sale debt securities which was deemed to be to be other-than-temporary.
Leases	Leases Effective January 1, 2019, the Company adopted Accounting Standards Update (ASU) 2016-02, Leases Leases Under Topic 842, the Company classifies its leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase by the Company. Lease classification is evaluated at the inception of the lease agreement. Regardless of classification, the Company records a right-of-use asset and a lease liability for all leases with a term greater than 12 months. All of the Company’s leases as of September 30, 2019 have been classified as operating leases. Operating lease expense is recognized on a straight-line basis over the term of the lease, with the exception of variable lease expenses which are recognized as incurred. The Company identifies leases in its contracts if the contract conveys the right to control the use of identified property, plant or equipment for a period of time in exchange for consideration. The Company does not allocate lease consideration between lease and nonlease components and records a lease liability equal to the present value of the remaining fixed consideration under the lease. The interest rates implicit in the Company’s leases are generally not readily determinable. Accordingly, the Company uses its estimated incremental borrowing rate at the commencement date of the lease to determine the present value discount of the lease liability. The Company estimates its incremental borrowing rate for each lease based on an evaluation of its expected credit rating and the prevailing market rates for collateralized debt in a similar economic environment with similar payment terms and maturity dates commensurate with the term of the lease. The right-of-use asset for each lease is equal to the lease liability, adjusted for unamortized initial direct costs and lease incentives and prepaid or accrued rent. Initial direct costs of entering into a lease are included in the right-of-use asset and amortized as lease expense over the term of the lease. Lease incentives, such as tenant improvements allowances, are recorded as a reduction of the right-of-use asset and amortized as a reduction of lease expense over the term of the lease. The Company excludes options to extend or terminate leases from the calculation of the lease liability unless it is reasonably certain the option will be exercised.
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. 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.
Revenue Recognition	Revenue Recognition The Company recognizes revenue in accordance with ASC 606, Revenue from Contracts with Customers The Company applies the five-step model to contracts that are within the scope of Topic 606 only when it is probable that the Company will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, for contracts within the scope of Topic 606, the Company assesses the goods or services promised within each contract and determine those that are performance obligations and whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to respective performance obligations when (or as) the respective performance obligations are satisfied. The Company evaluates its contracts with customers for the presence of significant financing components. If a significant financing component is identified in a contract and provides a financing benefit to the customer, the transaction price for the contract is adjusted to account for the financing portion of the arrangement, which is recognized as interest income over the financing term using the effective interest method. In determining the appropriate interest rates for significant financing components, the Company evaluates the credit profile of the customer and prevailing market interest rates and selects an interest rate in which it believes would be charged to the customer in a separate financing arrangement over a similar financing term. License and Royalty Revenue The Company licenses its NAV Technology Platform to other biotechnology and pharmaceutical companies. The terms of the licenses vary, and licenses may be exclusive or non-exclusive and may be sublicensable by the licensee. Licenses may grant intellectual property rights for purposes of internal and preclinical research and development only, or may include the rights, or options to obtain future rights, to commercialize drug therapies for specific diseases using the Company’s NAV Technology Platform. License agreements generally have a term at least equal to the life of the underlying patents, but are terminable at the option of the licensee. Consideration payable 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. The Company’s license agreements are accounted for as contracts with customers within the scope of Topic 606. At the inception of each license agreement, the Company determines the contract term for purposes of applying the requirements of Topic 606. Licenses are generally terminable at the option of the licensee with advance notice to the Company. For each license, the Company evaluates these termination rights to determine whether a substantive termination penalty would be incurred by the licensee upon termination. If the licensee incurs a substantive termination penalty upon termination, the contract term for revenue recognition purposes is generally equal to the stated term of the license, which is the life of the underlying licensed patents. Alternatively, if the licensee does not incur a substantive termination penalty upon termination, the contract term for revenue recognition purposes may be shorter than the stated term of the license, in which case the termination rights may be accounted for as contract renewal options. The determination of whether a substantive termination penalty is associated with the termination rights requires significant judgment. In making this determination, the Company considers, among other things, the nature of the intellectual property rights that would be returned to the Company upon termination, including the exclusivity of the licensed rights and the stage of development of the licensed products, the payment terms, including the amount and timing of non-refundable or guaranteed payments, and the business purpose of the termination rights granted to the licensee. Generally, the most significant judgment in determining whether a substantive termination penalty exists is the related to amount of any up-front or guaranteed non-refundable payments relative to the amount of annual payments that may be avoided by the licensee upon termination of the license. The Company considers all of the facts and circumstances relevant to each license when making this determination. Performance obligations under the Company’s license agreements may include (i) the delivery of intellectual property licenses and (ii) options granted to licensees to acquire additional licenses to the extent the options represent material rights to the licensee. At the inception of each license agreement which contains options for the licensee to acquire additional licenses, or contract renewal options, the Company evaluates the options to determine whether they provide material rights to the licensee. In making this determination, the Company considers whether the options are priced at a discount to the standalone selling price for the underlying licenses. If an option is priced at a discount to the standalone selling price for the underlying license, the option is considered to be a material right to the licensee and is accounted for as a separate performance obligation under the current license agreement. The Company evaluates the transaction price of its license agreements at the inception of each agreement and at each reporting date. The transaction price includes the fixed consideration payable to the Company during the contract term, as well as any variable consideration to the extent that it is probable that a significant reversal of revenue will not occur in the future. Fixed consideration under the license agreements includes up-front and annual fees payable during the contract term. Variable consideration under the license agreements includes development and sales-based milestone payments, sublicense fees and royalties on sales of licensed products. Consideration contingent upon the exercise of options by a licensee is excluded from the transaction price and not accounted for as part of the license agreement until the option is exercised. The transaction price for each license agreement is allocated to the underlying performance obligations and recognized as revenue when the performance obligations are satisfied. Consideration allocated to performance obligations for the delivery of an intellectual property license is recognized as revenue in full upon the delivery of the license to the licensee. Consideration allocated to performance obligations for license options is recognized as revenue in full upon the earlier of the option exercise or expiration. The exercise of a license option by a licensee is accounted for as a new license for revenue recognition purposes. Up-front and annual licenses fees payable to the Company over the contract term of each license are included in the transaction price, and the portion of this consideration that is allocated to the performance obligation for the delivery of the intellectual property license is recognized as revenue in full upon the delivery of the license to the licensee. If annual license fees are payable to the Company in periods beyond 12 months from the delivery of the license, a significant financing component is deemed to exist which provides a financing benefit to the licensee. If a significant financing component is identified, the Company adjusts the transaction price for the license to include only the present value of the annual license fees payable to the Company over the contract term. The discounted portion of the license fees is recognized as interest income from licensing over the financing period of the license. Development milestone payments are payable to the Company upon the achievement of specified development milestones by licensees. At the inception of each license agreement that contains development milestone payments, the Company evaluates whether the milestones are considered probable of achievement and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal will not occur in the future, milestone payments are included in the transaction price and recognized as revenue upon the delivery of the license. Milestone payments contingent on the achievement of development milestones that are not within the control of the Company or the licensee, such as regulatory approvals, are not considered probable of being achieved and are excluded from the transaction price until the milestone is achieved. At each reporting date, the Company re-evaluates the probability of achievement of outstanding development milestones and, if necessary, adjusts the transaction price for any milestones for which the probability of achievement has changed due to current facts and circumstances. Any such adjustments are recorded on a cumulative catch-up basis and recognized as revenue in the period of the adjustment. Royalties on sales of licensed products, sales-based milestone payments and sublicense fees based on the receipt of certain fees by licensees from any sublicensees are excluded from the transaction price of each license and recognized as revenue in the period that the related sales or sublicenses occur, provided that the associated license has been delivered to the licensee. Royalty revenue to date consists of royalties on net sales of Zolgensma®, which is marketed by AveXis, Inc. (AveXis), a wholly owned subsidiary of Novartis AG (Novartis). Zolgensma is a licensed product under the Company’s March 2014 license agreement, as amended, with AveXis for the development and commercialization of treatments for spinal muscular atrophy (SMA). The Company recognizes royalty revenue from net sales of Zolgensma in the period in which the underlying products are sold by AveXis, which in certain cases may require the Company to estimate royalty revenue for periods of net sales which have not yet been reported to the Company. Sales-based milestone payments related to net sales of Zolgensma are recognized as royalty revenue in the period in which the milestone is achieved. The Company receives payments from licensees based on the billing schedules established in each license agreement. Amounts recognized as revenue which have not yet been received from licensees, including unbilled royalties, are recorded as accounts receivable when the Company’s rights to the consideration are conditional solely upon the passage of time. Amounts recognized as revenue which have not yet been received from licensees are recorded as contract assets when the Company’s rights to the consideration are not unconditional. Contract assets are recorded as other current assets on the consolidated balance sheets. 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 consideration recorded as accounts receivable or contract assets which is not contractually payable by the licensee is charged off as a reduction of license revenue in the period of the termination. Amounts received by the Company prior to the delivery of underlying performance obligations are deferred and recognized as revenue upon the satisfaction of the performance obligations by the Company. Deferred revenue which is not expected to be recognized within 12 months from the reporting date is recorded as non-current on the consolidated balance sheets.
Cost of Revenues	Cost of Revenues Cost of revenues consists primarily of sublicense fees, milestone payments and royalties on net sales of licensed products as specified in the Company’s agreements with its licensors. Sublicense fees are based on a percentage of license fees received by the Company from NAV Technology Licensees and are recognized in the period that the underlying revenue is recognized. Milestone payments are payable to licensors upon the achievement of specified milestones by NAV Technology Licensees and are recognized in the period the milestone is achieved or deemed probable of achievement. Royalties are based on a percentage of net sales of licensed products by NAV Technology Licensees and are recognized in the period that the underlying sales occur. Amounts which are payable to licensors in periods beyond 12 months from the reporting date are recorded as non-current liabilities on the consolidated balance sheets.
Collaborative Arrangements	Collaborative Arrangements The Company evaluates its collaboration arrangements to determine whether they are within the scope of ASC 808, Collaborative Arrangements
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 Adoption of ASU 2016-02, Leases In February 2016, the Financial Accounting Standards Board (FASB) issued ASU 2016-02, Leases Leases The Company elected certain practical expedients allowed by Topic 842 for transition purposes, including the package of practical expedients which permitted the Company to not reassess lease identification, classification and initial direct costs under Topic 842 for leases that commenced prior to January 1, 2019. Additionally, the Company elected the practical expedient allowed for transition purposes to use hindsight in determining the terms of leases that commenced prior to January 1, 2019. Upon the adoption of Topic 842, the Company recorded operating lease right-of-use assets of $7.4 million and operating lease liabilities of $8.4 million for its leases which were in effect and had commenced prior to January 1, 2019 and had original lease terms of more than 12 months. The Company also derecognized current and non-current deferred rent liabilities of $1.4 million and prepaid expenses, other current assets and other assets of $0.4 million upon the adoption of Topic 842. Additionally, upon the adoption of Topic 842, the Company derecognized $5.9 million of property and equipment and $5.9 million of financing lease obligations related to construction-in-progress at 9800 Medical Center Drive, as the Company does not control the building during the construction period under the requirements of Topic 842. The lease term for the facility at 9800 Medical Center Drive does not commence until certain construction is completed by the landlord and the building is delivered to the Company. The right-of-use assets and lease liabilities related to the facility at 9800 Medical Center Drive will not be recognized on the Company’s consolidated balance sheets until the commencement date of the lease, which is expected to occur in 2020. The cumulative impact of the adoption of Topic 842 resulted in an increase in accumulated deficit of less than $0.1 million on January 1, 2019. The adoption of Topic 842 did not have a material impact on the Company’s results of operations for the three and nine months ended September 30, 2019, nor does the Company believe it will have a material impact on future results of operations based on its current leasing arrangements. Other Recently Adopted Accounting Pronouncements In November 2018, the FASB issued ASU 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction Between Topic 808 and Topic 606 In February 2018, the FASB issued ASU 2018-02, Income Statement—Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income Tax Cuts and Jobs Act of 2017 (the TCJA) In April 2017, the FASB issued ASU 2017-08, Receivables—Nonrefundable Fees and Other Costs (Subtopic 310-20) Recent Accounting Pronouncements Not Yet Adopted 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 August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement measurements. The standard is effective for the Company beginning January 1, 2020, with early adoption permitted upon issuance. The Company does not believe the application of this standard will have a material impact on its financial statement disclosures. In June 2016, the FASB issued ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2019
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, 2019 September 30, 2018 Cash and cash equivalents $ 79,594 $ 142,423 Restricted cash 1,053 225 Total cash and cash equivalents and restricted cash $ 80,647 $ 142,648

Marketable Securities (Tables)

Marketable Securities (Tables)	9 Months Ended
	Sep. 30, 2019
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 Unrealized Gains Unrealized Losses Fair Value September 30, 2019 U.S. government and federal agency securities $ 78,093 $ 296 $ (3 ) $ 78,386 Certificates of deposit 7,529 87 — 7,616 Corporate bonds 220,694 1,018 (21 ) 221,691 Equity securities 420 29,420 — 29,840 $ 306,736 $ 30,821 $ (24 ) $ 337,533 Amortized Cost Unrealized Gains Unrealized Losses Fair Value December 31, 2018 U.S. government and federal agency securities $ 103,410 $ 93 $ (37 ) $ 103,466 Certificates of deposit 8,992 — — 8,992 Corporate bonds 282,902 36 (377 ) 282,561 $ 395,304 $ 129 $ (414 ) $ 395,019
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, 2019 U.S. government and federal agency securities $ 4,497 $ (3 ) $ — $ — $ 4,497 $ (3 ) Corporate bonds 23,354 (21 ) — — 23,354 (21 ) $ 27,851 $ (24 ) $ — $ — $ 27,851 $ (24 ) Less than 12 Months 12 Months or Greater Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses December 31, 2018 U.S. government and federal agency securities $ 53,124 $ (37 ) $ — $ — $ 53,124 $ (37 ) Corporate bonds 245,283 (354 ) 12,424 (23 ) 257,707 (377 ) $ 298,407 $ (391 ) $ 12,424 $ (23 ) $ 310,831 $ (414 )

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2019
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, 2019 Cash equivalents: Money market mutual funds $ — $ 72,634 $ — $ 72,634 Corporate bonds — 5,905 — 5,905 Total cash equivalents — 78,539 — 78,539 Marketable securities: U.S. government and federal agency securities — 78,386 — 78,386 Certificates of deposit — 7,616 — 7,616 Corporate bonds — 221,691 — 221,691 Equity securities 29,840 — — 29,840 Total marketable securities 29,840 307,693 — 337,533 Total cash equivalents and marketable securities $ 29,840 $ 386,232 $ — $ 416,072 Quoted Significant prices other Significant in active observable unobservable markets inputs inputs (Level 1) (Level 2) (Level 3) Total December 31, 2018 Cash equivalents: Money market mutual funds $ — $ 75,542 $ — $ 75,542 Total cash equivalents — 75,542 — 75,542 Marketable securities: U.S. government and federal agency securities — 103,466 — 103,466 Certificates of deposit — 8,992 — 8,992 Corporate bonds — 282,561 — 282,561 Total marketable securities — 395,019 — 395,019 Total cash equivalents and marketable securities $ — $ 470,561 $ — $ 470,561

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	9 Months Ended
	Sep. 30, 2019
Property Plant And Equipment [Abstract]
Schedule of Property and Equipment	Property and equipment, net consists of the following (in thousands): September 30, 2019 December 31, 2018 Lab equipment $ 18,492 $ 14,417 Computer equipment and software 2,448 2,002 Furniture and fixtures 1,960 1,915 Leasehold improvements 17,831 11,751 Construction-in-progress — 5,854 Total property and equipment 40,731 35,939 Accumulated depreciation and amortization (12,444 ) (7,237 ) Property and equipment, net $ 28,287 $ 28,702

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2019
Leases [Abstract]
Summary of Lease Costs and Supplemental Cash Flow Information of 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, 2019 September 30, 2019 Operating lease cost $ 690 $ 2,088 Variable lease cost 164 463 Total lease cost $ 854 $ 2,551 Cash paid for amounts included in operating lease liabilities $ 757 $ 2,152 Right-of-use assets acquired through operating lease liabilities $ 557 $ 222
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, 2019 Weighted-average remaining lease term (years) 2.7 Weighted-average discount rate 5.5 %
Reconciliation of Undiscounted Future Minimum Lease Payments Remaining Under Leases that Have Not Yet Commenced and Other Operating Leases	The following table presents a reconciliation of the undiscounted future minimum lease payments remaining under leases that have not yet commenced and other operating leases to the amounts reported as operating lease liabilities on the consolidated balance sheet as of September 30, 2019 (in thousands): Leases Other Total Not Yet Operating Minimum Lease Commenced (a) Leases Payments Undiscounted future minimum lease payments: 2019 (remainder of year) $ 73 $ 521 $ 594 2020 413 3,057 3,470 2021 2,306 2,662 4,968 2022 5,420 631 6,051 2023 6,369 479 6,848 Thereafter 83,731 — 83,731 Total undiscounted future minimum lease payments $ 98,312 $ 7,350 $ 105,662 Amount representing imputed interest (524 ) Total operating lease liabilities 6,826 Current portion of operating lease liabilities (2,506 ) Operating lease liabilities, non-current $ 4,320 (a) Includes undiscounted future minimum lease payments under the 9800 Medical Center Drive Lease and 400 Madison Lease which are not included in the lease liabilities reported on the consolidated balance sheet as of September 30, 2019. The actual timing and amounts of these payments are subject to adjustment based on the commencement dates and actual square footage of the leased premises. Accordingly, these amounts were estimates as of September 30 , 2019.
Schedule of Future Minimum Lease Payments Under Topic 840 for 9800 Medical Center Drive Lease and Other Operating Leases	As of December 31, 2018, future minimum lease payments under Topic 840 for the 9800 Medical Center Drive Lease and other operating leases were as follows (in thousands): 9800 Medical Other Total Center Drive Operating Minimum Lease Lease (a) Leases Payments 2019 $ — $ 2,798 $ 2,798 2020 — 3,054 3,054 2021 1,329 2,391 3,720 2022 4,289 621 4,910 2023 5,156 479 5,635 Thereafter 76,420 — 76,420 Total minimum lease payments $ 87,194 $ 9,343 $ 96,537 (a) Includes all future minimum lease payments under the 9800 Medical Center Drive Lease, including amounts recorded as financing lease obligations on the consolidated balance sheet . The actual timing and amounts of payments under the 9800 Medical Center Drive Lease are subject to adjustment based on the commencement date and actual square footage of the leased premises. Accordingly, these amounts were estimates as of December 31, 2018.

License and Royalty Revenue (Ta

License and Royalty Revenue (Tables)	9 Months Ended
	Sep. 30, 2019
License Agreement Revenue Recognition [Abstract]
Summary of Changes in Balances of Receivables, Contract Assets and Contract Liabilities	The following tables present changes in the balances of the Company’s receivables, contract assets and contract liabilities during the periods presented (in thousands): Balance at Beginning Net Additions Balance at of Period (Deductions) End of Period Three Months Ended September 30, 2019 Receivables and contract assets: Accounts receivable, current and non-current $ 33,634 $ 9,886 $ 43,520 Contract assets $ — $ — $ — Contract liabilities: Deferred revenue, current and non-current $ 3,333 $ — $ 3,333 Balance at Beginning Net Additions Balance at of Period (Deductions) End of Period Nine Months Ended September 30, 2019 Receivables and contract assets: Accounts receivable, current and non-current $ 31,599 $ 11,921 $ 43,520 Contract assets $ 750 $ (750 ) $ — Contract liabilities: Deferred revenue, current and non-current $ 3,933 $ (600 ) $ 3,333 Balance at Beginning Net Additions Balance at of Period (Deductions) End of Period Three Months Ended September 30, 2018 Receivables and contract assets: Accounts receivable, current and non-current $ 5,224 $ 2,002 $ 7,226 Contract assets $ — $ 2,000 $ 2,000 Contract liabilities: Deferred revenue, current and non-current $ 600 $ — $ 600 Balance at Beginning Net Additions Balance at of Period (Deductions) End of Period Nine Months Ended September 30, 2018 Receivables and contract assets: Accounts receivable, current and non-current $ 5,850 $ 1,376 $ 7,226 Contract assets $ 350 $ 1,650 $ 2,000 Contract liabilities: Deferred revenue, current and non-current $ — $ 600 $ 600
Schedule of License Revenue	The Company recognized the following amounts under the March 2014 License with AveXis, as amended, which include amounts from both the original March 2014 License and the January 2018 Amendment (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 License revenue $ — $ 4,000 $ 3,500 $ 176,066 Zolgensma royalty revenue 9,182 — 10,106 — Total license and royalty revenue $ 9,182 $ 4,000 $ 13,606 $ 176,066 Interest income from licensing $ 7 $ 8 $ 22 $ 7,958

Stock-based Compensation (Table

Stock-based Compensation (Tables)	9 Months Ended
	Sep. 30, 2019
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, 2019 2018 2019 2018 Stock options $ 6,965 $ 4,309 $ 19,261 $ 11,248 Restricted stock units 69 69 206 206 Employee stock purchase plan 128 105 512 301 $ 7,162 $ 4,483 $ 19,979 $ 11,755
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, 2019 2018 2019 2018 Research and development $ 3,657 $ 1,940 $ 9,530 $ 5,364 General and administrative 3,505 2,543 10,449 6,391 $ 7,162 $ 4,483 $ 19,979 $ 11,755
Summary of Unvested RSUs Activity Under 2015 Plan	The following table summarizes restricted stock unit activity under the 2015 Plan (in thousands, except per share data): Weighted- average Grant Date Shares Fair Value Unvested balance at December 31, 2018 40 $ 20.90 Granted — $ — Vested — $ — Forfeited — $ — Unvested balance at September 30, 2019 40 $ 20.90
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, 2018 4,855 $ 19.31 7.6 $ 118,185 Granted 1,596 $ 47.82 Exercised (684 ) $ 8.07 Cancelled or forfeited (237 ) $ 33.74 Outstanding at September 30, 2019 5,530 $ 28.31 7.7 $ 69,769 Exercisable at September 30, 2019 2,827 $ 15.48 6.6 $ 60,340 Vested and expected to vest at September 30, 2019 5,530 $ 28.31 7.7 $ 69,769 (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 Income (Loss) Per Share (Ta

Net Income (Loss) Per Share (Tables)	9 Months Ended
	Sep. 30, 2019
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 are as follows (in thousands, except per share data): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Basic net income (loss) per share: Net income (loss) applicable to common stockholders $ (34,584 ) $ (19,202 ) $ (68,269 ) $ 95,631 Shares used in computation: Weighted-average common shares outstanding 36,813 33,988 36,618 32,576 Basic net income (loss) per share $ (0.94 ) $ (0.56 ) $ (1.86 ) $ 2.94 Diluted net income (loss) per share: Net income (loss) applicable to common stockholders $ (34,584 ) $ (19,202 ) $ (68,269 ) $ 95,631 Shares used in computation: Weighted-average common shares outstanding 36,813 33,988 36,618 32,576 Stock options — — — 3,268 Restricted stock units — — — 31 Weighted-average diluted common shares 36,813 33,988 36,618 35,875 Diluted net income (loss) per share $ (0.94 ) $ (0.56 ) $ (1.86 ) $ 2.67
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, 2019 2018 2019 2018 Stock options issued and outstanding 5,530 5,171 5,530 1,128 Unvested restricted stock units outstanding 40 40 40 — Employee stock purchase plan 16 4 16 4 5,586 5,215 5,586 1,132

Supplemental Disclosures (Table

Supplemental Disclosures (Tables)	9 Months Ended
	Sep. 30, 2019
Payables And Accruals [Abstract]
Schedules of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consists of the following (in thousands): September 30, 2019 December 31, 2018 Accrued personnel costs $ 8,869 $ 9,484 Accrued external research and development expenses 4,390 4,274 Accrued sublicense fees and royalties 3,245 1,617 Accrued external general and administrative expenses 1,137 773 Accrued income taxes payable 508 726 Accrued purchases of property and equipment 349 221 Other accrued expenses and current liabilities 733 69 $ 19,231 $ 17,164

Nature of Business - Additional

Nature of Business - Additional Information (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Accumulated deficit	$ (151,358)	$ (83,016)
Cash, cash equivalents and marketable securities	$ 417,100

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, 2019	Dec. 31, 2018	Sep. 30, 2018
Accounting Policies [Abstract]
Cash and cash equivalents	$ 79,594	$ 75,561	$ 142,423
Restricted cash	1,053	$ 1,053	225
Total cash and cash equivalents and restricted cash	$ 80,647		$ 142,648

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	Jan. 01, 2019	Sep. 30, 2019	Dec. 31, 2018
Significant Accounting Policies [Line Items]
Impairment of available-for-sale securities deemed to be other-than-temporary		$ 0
Operating lease right-of-use assets		5,905,000
Property and equipment, net		28,287,000	$ 28,702,000
Accumulated deficit		$ (151,358,000)	$ (83,016,000)
ASU 2016-02 [Member]
Significant Accounting Policies [Line Items]
Operating lease right-of-use assets	$ 7,400,000
Operating lease liabilities	8,400,000
ASU 2016-02 [Member] | Maximum [Member]
Significant Accounting Policies [Line Items]
Accumulated deficit	100,000
ASU 2016-02 [Member] | Restatement Adjustment [Member]
Significant Accounting Policies [Line Items]
Current and noncurrent deferred rent liabilities	1,400,000
Prepaid expenses, other current assets and other assets	400,000
ASU 2016-02 [Member] | Restatement Adjustment [Member] | 9800 Medical Center Drive Lease [Member]
Significant Accounting Policies [Line Items]
Property and equipment, net	(5,900,000)
Financing lease obligation	(5,900,000)
ASU 2018-02 [Member] | Maximum [Member]
Significant Accounting Policies [Line Items]
Reclassification of stranded tax effects of unrealized gains and losses on available-for-sale securities from accumulated other comprehensive income (loss) to accumulated deficit	$ 100,000

Marketable Securities - Summary

Marketable Securities - Summary of Company Marketable Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 306,736	$ 395,304
Unrealized Gains	30,821	129
Unrealized Losses	(24)	(414)
Fair Value	337,533	395,019
U.S. Government and Federal Agency Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	78,093	103,410
Unrealized Gains	296	93
Unrealized Losses	(3)	(37)
Fair Value	78,386	103,466
Certificates of Deposit [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	7,529	8,992
Unrealized Gains	87
Fair Value	7,616	8,992
Corporate Bonds [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	220,694	282,902
Unrealized Gains	1,018	36
Unrealized Losses	(21)	(377)
Fair Value	221,691	$ 282,561
Equity Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	420
Unrealized Gains	29,420
Fair Value	$ 29,840

Marketable Securities - Additio

Marketable Securities - Additional Information (Detail)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019USD ($)Security	Sep. 30, 2018USD ($)	Sep. 30, 2019USD ($)Security	Sep. 30, 2018USD ($)	Dec. 31, 2018USD ($)
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	(100,000)	$ 100,000	1,700,000	$ 200,000
Unrealized gains (losses) on available-for-sale debt securities, income tax benefit (expense)	$ 100,000	0	$ (600,000)	0
Number of investment grade fixed income debt security | Security	7		7
Other-than-temporary impaired			$ 0		$ 0
Non-marketable equity securities, carrying value	$ 400,000		400,000
Marketable securities realized			0
Equity Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Marketable securities unrealized gain (loss)	(2,200,000)		29,400,000
Maximum [Member]
Schedule Of Available For Sale Securities [Line Items]
Unrealized gains (losses) on available-for-sale debt securities, income tax benefit (expense)	100,000		(600,000)
Investment Income [Member] | Maximum [Member]
Schedule Of Available For Sale Securities [Line Items]
Net realized gains or losses available for sale debt 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, 2019	Dec. 31, 2018
Schedule Of Available For Sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 27,851
Less than 12 Months, Unrealized Losses	(24)	$ (391)
12 Months or Greater, Unrealized Losses		(23)
Total, Fair Value	27,851
Total, Unrealized Losses	(24)	(414)
Less than 12 Months, Fair Value		298,407
12 Months or Greater, Fair Value		12,424
Total, Fair Value		310,831
U.S. Government and Federal Agency Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than 12 Months, Fair Value	4,497
Less than 12 Months, Unrealized Losses	(3)	(37)
Total, Fair Value	4,497
Total, Unrealized Losses	(3)	(37)
Less than 12 Months, Fair Value		53,124
Total, Fair Value		53,124
Corporate Bonds [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than 12 Months, Fair Value	23,354
Less than 12 Months, Unrealized Losses	(21)	(354)
12 Months or Greater, Unrealized Losses		(23)
Total, Fair Value	23,354
Total, Unrealized Losses	$ (21)	(377)
Less than 12 Months, Fair Value		245,283
12 Months or Greater, Fair Value		12,424
Total, Fair Value		$ 257,707

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, 2019	Dec. 31, 2018
Marketable securities:
Fair Value	$ 337,533	$ 395,019
Cash Equivalents and Marketable Securities [Member]
Marketable securities:
Total cash equivalents and marketable securities	416,072	470,561
Corporate Bonds [Member]
Marketable securities:
Fair Value	221,691	282,561
Cash Equivalents [Member]
Cash equivalents:
Total cash equivalents	78,539	75,542
Cash Equivalents [Member] | Corporate Bonds [Member]
Cash equivalents:
Total cash equivalents	5,905
U.S. Government and Federal Agency Securities [Member]
Marketable securities:
Fair Value	78,386	103,466
Certificates of Deposit [Member]
Marketable securities:
Fair Value	7,616	8,992
Equity Securities [Member]
Marketable securities:
Fair Value	29,840
Money Market Mutual Funds [Member] | Cash Equivalents [Member]
Cash equivalents:
Total cash equivalents	72,634	75,542
Quoted Prices in Active Markets (Level 1) [Member]
Marketable securities:
Fair Value	29,840
Quoted Prices in Active Markets (Level 1) [Member] | Cash Equivalents and Marketable Securities [Member]
Marketable securities:
Total cash equivalents and marketable securities	29,840
Quoted Prices in Active Markets (Level 1) [Member] | Equity Securities [Member]
Marketable securities:
Fair Value	29,840
Significant Other Observable Inputs (Level 2) [Member]
Marketable securities:
Fair Value	307,693	395,019
Significant Other Observable Inputs (Level 2) [Member] | Cash Equivalents and Marketable Securities [Member]
Marketable securities:
Total cash equivalents and marketable securities	386,232	470,561
Significant Other Observable Inputs (Level 2) [Member] | Corporate Bonds [Member]
Marketable securities:
Fair Value	221,691	282,561
Significant Other Observable Inputs (Level 2) [Member] | Cash Equivalents [Member]
Cash equivalents:
Total cash equivalents	78,539	75,542
Significant Other Observable Inputs (Level 2) [Member] | Cash Equivalents [Member] | Corporate Bonds [Member]
Cash equivalents:
Total cash equivalents	5,905
Significant Other Observable Inputs (Level 2) [Member] | U.S. Government and Federal Agency Securities [Member]
Marketable securities:
Fair Value	78,386	103,466
Significant Other Observable Inputs (Level 2) [Member] | Certificates of Deposit [Member]
Marketable securities:
Fair Value	7,616	8,992
Significant Other Observable Inputs (Level 2) [Member] | Money Market Mutual Funds [Member] | Cash Equivalents [Member]
Cash equivalents:
Total cash equivalents	$ 72,634	$ 75,542

Fair Value of Financial Instr_4

Fair Value of Financial Instruments - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Fair value hierarchy level 1 to level 2 transfers amount	$ 0		$ 0
Fair value hierarchy level 2 to level 1 transfers amount	0		0
Non-marketable equity securities					$ 400,000
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, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Total property and equipment	$ 40,731	$ 35,939
Accumulated depreciation and amortization	(12,444)	(7,237)
Property and equipment, net	28,287	28,702
Lab Equipment [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	18,492	14,417
Computer Equipment and Software [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	2,448	2,002
Furniture and Fixtures [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	1,960	1,915
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	$ 17,831	11,751
Construction in Progress [Member]
Property Plant And Equipment [Line Items]
Total property and equipment		$ 5,854

Property and Equipment Net - Ad

Property and Equipment Net - Additional Information (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Property and equipment, net	$ 28,287		$ 28,702
ASU 2016-02 [Member] | Restatement Adjustment [Member] | 9800 Medical Center Drive Lease [Member]
Property Plant And Equipment [Line Items]
Property and equipment, net		$ (5,900)

Leases - Additional Information

Leases - Additional Information (Detail)	1 Months Ended								9 Months Ended
	Nov. 30, 2019USD ($)ft²	Oct. 31, 2019USD ($)	May 31, 2019	Nov. 30, 2018USD ($)ft²	Apr. 30, 2018USD ($)	May 31, 2016USD ($)	Jan. 31, 2016USD ($)	Mar. 31, 2015	Sep. 30, 2019USD ($)	Jan. 01, 2019USD ($)	Dec. 31, 2018USD ($)
Other Commitments [Line Items]
Property and equipment, net									$ 28,287,000		$ 28,702,000
Financing lease obligation											$ 5,854,000
Operating lease liabilities									(1,832,000)
Decrease in right-of-use assets									(1,712,000)
Operating lease right-of-use assets									5,905,000
Operating lease liabilities									$ 2,506,000
ASU 2016-02 [Member]
Other Commitments [Line Items]
Operating lease right-of-use assets										$ 7,400,000
Rockville, Maryland [Member]
Other Commitments [Line Items]
Operating leases expiration year									2022
9800 Medical Center Drive Lease [Member] | Subsequent Event
Other Commitments [Line Items]
Tenant improvement allowance to be received	$ 19,500,000
Number of square feet to be constructed | ft²	38,000
Additional Lease Rental Payments	$ 22,600,000
9800 Medical Center Drive Lease [Member] | Leasehold Improvements [Member]
Other Commitments [Line Items]
Property and equipment, net									$ 5,400,000
9800 Medical Center Drive Lease [Member] | ASU 2016-02 [Member] | Restatement Adjustment [Member]
Other Commitments [Line Items]
Property and equipment, net										(5,900,000)
Financing lease obligation										$ (5,900,000)
9800 Medical Center Drive Lease [Member] | Rockville, Maryland [Member]
Other Commitments [Line Items]
Lease Expiration Term				16 years
Construction completion, description									The initial construction of the building is being conducted by the landlord and is expected to be completed in 2020
Tenant improvement allowance to be received				$ 15,300,000
Lease not yet commenced, option to extend the lease									true
Lease not yet commenced, additional lease term				10 years
Lease not yet commenced, option to terminate the lease									true
Lease not yet commenced, option to terminate the lease, description									the option to terminate the lease after 12 years from the delivery of the leased premises to the Company. If the Company elects to terminate the lease, it will be subject to a termination fee equal to the unamortized tenant improvement allowance, rent abatement and landlord commissions as of the termination date, bearing interest at 5% per annum, plus four months of base rent and operating expenses.
Minimum release term for option to terminate				12 years
Percentage of early termination fee				5.00%
Term of required base rent to be paid as termination fee				4 months
Frequency of periodic payment									Monthly payments under the 9800 Medical Center Drive Lease begin approximately 12 months from the delivery of the leased premises to the Company and escalate annually in accordance with the lease agreement.
Periodic payment term, from the delivery of leased premises				12 months
Letters of credit				$ 800,000
Number of square feet to be constructed | ft²				139,000
9712 Medical Center Drive [Member] | Rockville, Maryland [Member]
Other Commitments [Line Items]
Lease term commenced date								2015-04
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
Tenant improvement allowance received					$ 400,000
9600 Blackwell Road [Member] | Rockville, Maryland [Member]
Other Commitments [Line Items]
Percentage of early termination fee							8.00%
Lease term commenced date							2016-02
Operating lease, existence of option to extend the lease									true
Additional lease term under option to extend							5 years
Tenant improvement allowance received							$ 800,000
Lease expiration date							Sep. 30, 2023
Required period to terminate lease after commencement period							67 months
400 Madison Avenue [Member] | 400 Madison Lease [Member]
Other Commitments [Line Items]
Letters of credit						$ 200,000
Operating leases commencement year						2016-07
Operating lease expiration year			2020-10
400 Madison Avenue [Member] | 400 Madison Lease [Member] | Lease Amendment [Member]
Other Commitments [Line Items]
Operating lease expiration year									2019-08
Operating lease liabilities									$ 400,000
Decrease in right-of-use assets									400,000
Operating lease right-of-use assets									0
Operating lease liabilities									$ 0
400 Madison Avenue [Member] | 400 Madison Lease [Member] | Lease Amendment [Member] | Subsequent Event
Other Commitments [Line Items]
Tenant improvement allowance to be received		$ 700,000
Operating leases expiration term		7 years 6 months

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, 2019	Sep. 30, 2019
Leases [Abstract]
Operating lease cost	$ 690	$ 2,088
Variable lease cost	164	463
Total lease cost	854	2,551
Cash paid for amounts included in operating lease liabilities	757	2,152
Right-of-use assets acquired through operating lease liabilities	$ 557	$ 222

Leases - Weighted-Average Remai

Leases - Weighted-Average Remaining Lease Term and Weighted-Average Discount Rate of Operating Leases (Detail)	Sep. 30, 2019
Leases [Abstract]
Weighted-average remaining lease term (years)	2 years 8 months 12 days
Weighted-average discount rate	5.50%

Leases - Reconciliation of Undi

Leases - Reconciliation of Undiscounted Future Minimum Lease Payments Remaining Under Leases that Have Not Yet Commenced and Other Operating Leases (Detail) $ in Thousands	Sep. 30, 2019USD ($)
Undiscounted future minimum lease payments:
2019 (remainder of year)	$ 594
2020	3,470
2021	4,968
2022	6,051
2023	6,848
Thereafter	83,731
Total undiscounted future minimum lease payments	105,662
Current portion of operating lease liabilities	(2,506)
Operating lease liabilities, non-current	4,320
Leases Not Yet Commenced [Member]
Undiscounted future minimum lease payments:
2019 (remainder of year)	73
2020	413
2021	2,306
2022	5,420
2023	6,369
Thereafter	83,731
Total undiscounted future minimum lease payments	98,312
Other Operating leases [Member]
Undiscounted future minimum lease payments:
2019 (remainder of year)	521
2020	3,057
2021	2,662
2022	631
2023	479
Total undiscounted future minimum lease payments	7,350
Amount representing imputed interest	(524)
Total operating lease liabilities	6,826
Current portion of operating lease liabilities	(2,506)
Operating lease liabilities, non-current	$ 4,320

Leases - Schedule of Future Min

Leases - Schedule of Future Minimum Lease Payments Under Topic 840 for 9800 Medical Center Drive Lease and Other Operating Leases (Detail) $ in Thousands	Dec. 31, 2018USD ($)
Lessee Lease Description [Line Items]
2019	$ 2,798
2020	3,054
2021	3,720
2022	4,910
2023	5,635
Thereafter	76,420
Total minimum lease payments	96,537
9800 Medical Center Drive Lease [Member]
Lessee Lease Description [Line Items]
2021	1,329
2022	4,289
2023	5,156
Thereafter	76,420
Total minimum lease payments	87,194
Other Operating leases [Member]
Lessee Lease Description [Line Items]
2019	2,798
2020	3,054
2021	2,391
2022	621
2023	479
Total minimum lease payments	$ 9,343

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($)	1 Months Ended		3 Months Ended		9 Months Ended
	Oct. 31, 2019	Jul. 31, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Apr. 30, 2019
Other Commitments [Line Items]
Research and development			$ 35,692,000	$ 18,508,000	$ 90,378,000	$ 59,544,000
European Patent Office Proceeding [Member]
Other Commitments [Line Items]
Liability related to third party opposition			0		0
University of Pennsylvania [Member] | Maximum [Member]
Other Commitments [Line Items]
Upfront fee, milestone fees							$ 20,500,000
Neurimmune AG [Member]
Other Commitments [Line Items]
Period for sharing of research and development cost		2 years
Percentage of partnership in collaboration		50.00%
Neurimmune AG [Member] | Maximum [Member]
Other Commitments [Line Items]
Research and development			$ 100,000		$ 100,000
Clearside Biomedical Inc. [Member] | Subsequent Event
Other Commitments [Line Items]
Payments against exercise of license option	$ 1,600,000
Clearside Biomedical Inc. [Member] | Maximum [Member] | Subsequent Event
Other Commitments [Line Items]
Upfront fee, milestone fees	$ 136,000,000

License and Royalty Revenue - A

License and Royalty Revenue - Additional Information (Detail)	1 Months Ended			3 Months Ended		9 Months Ended
	May 31, 2018USD ($)	Jan. 31, 2018USD ($)	Mar. 31, 2014USD ($)	Sep. 30, 2019USD ($)ProductCandidate	Sep. 30, 2018USD ($)	Sep. 30, 2019USD ($)ProductCandidate	Sep. 30, 2018USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Jun. 30, 2018USD ($)	Dec. 31, 2017USD ($)
License Revenue [Line Items]
Milestone payment upon commencement of clinical trials in humans						$ 20,100,000
Milestone payment upon submission of regulatory approval filings						31,000,000
Milestone payment upon approval of commercial products by regulatory agencies						96,000,000
Milestone payment upon achievement of specified sales targets for licensed products						207,000,000
Royalty revenue				$ 9,182,000	$ 4,000,000	13,606,000	$ 176,066,000
Accounts receivable				43,520,000	7,226,000	43,520,000	7,226,000	$ 33,634,000		$ 31,599,000	$ 5,224,000	$ 5,850,000
Deferred revenue, current and non-current				3,333,000	600,000	3,333,000	600,000	3,333,000		3,933,000	600,000
Licenses revenue				14,700,000	5,306,000	23,465,000	177,728,000
Impirment losses on receivables or contract assets						0
Total current and non-current accounts receivable				43,520,000	7,226,000	43,520,000	7,226,000	$ 33,634,000		31,599,000	$ 5,224,000	$ 5,850,000
Billed to customers				1,200,000		1,200,000				400,000
Billable to customers in future periods				42,400,000		42,400,000				31,200,000
Allowance for doubtful accounts				0		$ 0				0
Transaction price description						Upon its execution, the transaction price of the January 2018 Amendment was $132.1 million, which was fully recognized as license revenue upon the delivery of the modified license in January 2018. In May 2018, as a result of the acquisition of AveXis by Novartis, the transaction price was increased by $40.0 million to account for the acceleration of the sale-based milestone which was previously excluded from the transaction price. The $40.0 million increase in the transaction price was recognized as license revenue upon the completion of the change of control in May 2018 since the amended license had been fully delivered to AveXis. Additionally, due to the acceleration of the two $30.0 million payments originally due in January 2019 and January 2020, the Company recognized $6.1 million of interest income from licensing upon the completion of the change of control of AveXis, which represents the remaining present value discount on such payments as of the date of the change of control. As of September 30, 2019, the transaction price of the January 2018 Amendment was $172.1 million, which includes: (i) the $80.0 million payment in January 2018, (ii) the present value, as of the date of the January 2018 Amendment, of the two $30.0 million payments originally due in January 2019 and January 2020 and (iii) the $40.0 million sales-based milestone which was accelerated upon the change of control in May 2018. Variable consideration under the January 2018 Amendment, which has been excluded from the transaction price, includes the remaining sales-based milestone payment of $80.0 million, as well as any potential sublicense fees or royalties on sales of licensed products, which will be recognized in the period of the underlying sales or sublicenses.
Interest income from licensing				716,000	109,000	$ 2,091,000	8,362,000
Accounts receivable, current				19,175,000		19,175,000				8,587,000
AveXis, Inc. [Member]
License Revenue [Line Items]
Interest income from licensing				7,000	8,000	22,000	7,958,000
Zolgensma Royalties [Member]
License Revenue [Line Items]
Royalty revenue				9,182,000		10,106,000
License [Member]
License Revenue [Line Items]
Royalty revenue					4,000,000	3,500,000	176,066,000
Licenses revenue				$ 0	0	$ 600,000
NAV Technology Licensees [Member] | NAV Technology Platform [Member]
License Revenue [Line Items]
Number of commercial product candidates | ProductCandidate				1		1
NAV Technology Licensees [Member] | NAV Technology Platform [Member] | Minimum [Member]
License Revenue [Line Items]
Number of development product candidates | ProductCandidate				20		20
March 2014 Licence Agreement [Member] | AveXis, Inc. [Member]
License Revenue [Line Items]
Accounts receivable				$ 9,400,000		$ 9,400,000				200,000
Up-front fee paid			$ 2,000,000			2,000,000
Milestone fee payments upon achievement of various development and commercialization			$ 12,300,000
License agreement amendment date			2018-01
Transaction price of license				11,000,000		11,000,000
Payments for remaining development milestones				3,500,000		3,500,000
Increase in transaction price of license						3,500,000
Accounts receivable, current				9,200,000		9,200,000
Accounts receivable, non -current				200,000		200,000
March 2014 Licence Agreement [Member] | Maximum [Member] | AveXis, Inc. [Member]
License Revenue [Line Items]
Accounts receivable, current										100,000
Accounts receivable, non -current										200,000
March 2014 Licence Agreement [Member] | Zolgensma Royalties [Member] | AveXis, Inc. [Member]
License Revenue [Line Items]
Royalty revenue				9,200,000		10,100,000
Accounts receivable				9,200,000		9,200,000
Total current and non-current accounts receivable				9,200,000		9,200,000
License Agreement [Member] | License [Member]
License Revenue [Line Items]
License revenue				900,000	$ 4,100,000	4,600,000	$ 4,200,000
November 2018 License Agreement [Member] | Abeona Therapeutics Inc. [Member]
License Revenue [Line Items]
Accounts receivable				28,000,000		28,000,000				$ 26,000,000
January 2018 Amendment Agreement [Member] | AveXis, Inc. [Member]
License Revenue [Line Items]
License agreement period		14 years
License fee		$ 80,000,000
Sales-based milestone payment unpaid in the event of change of control		40,000,000
License fees received	$ 100,000,000
Transaction price of license		132,100,000		$ 172,100,000		172,100,000
Increase in transaction price of license						0
Interest income from licensing	6,100,000
Sales-based milestone payment exclude transaction price						$ 80,000,000
Payments due from related party									$ 30,000,000
Consideration payment due period one						2019-01
Consideration payment due period two						2020-01
January 2018 Amendment Agreement [Member] | AveXis, Inc. [Member] | Share-based Milestone [Member]
License Revenue [Line Items]
Increase in transaction price of license	40,000,000
January 2018 Amendment Agreement [Member] | AveXis, Inc. [Member] | First Anniversary [Member]
License Revenue [Line Items]
License fee		30,000,000
January 2018 Amendment Agreement [Member] | AveXis, Inc. [Member] | Second Anniversary [Member]
License Revenue [Line Items]
License fee		30,000,000
January 2018 Amendment Agreement [Member] | Minimum [Member] | AveXis, Inc. [Member]
License Revenue [Line Items]
Milestone payment		$ 120,000,000
January 2018 Amendment Agreement [Member] | License [Member] | AveXis, Inc. [Member]
License Revenue [Line Items]
Increase in transaction price of license	$ 40,000,000

License and Royalty Revenue - S

License and Royalty Revenue - Summary of Changes in Balances of Receivables, Contract Assets and Contract Liabilities (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Receivables and contract assets:
Accounts receivable, current and non-current, Balance at Beginning of Period	$ 33,634	$ 5,224	$ 31,599	$ 5,850
Accounts receivable, current and non-current, Net Additions (Deductions)	9,886	2,002	11,921	1,376
Accounts receivable, current and non-current, Balance at End of Period	43,520	7,226	43,520	7,226
Contract assets, Balance at Beginning of Period			750	350
Contract assets, Net Additions (Deductions)		2,000	(750)	1,650
Contract assets, Balance at End of Period		2,000		2,000
Contract liabilities:
Deferred revenue, current and non-current, Balance at Beginning of Period	3,333	600	3,933
Deferred revenue, Net Additions (Deductions)			(600)	600
Deferred revenue, current and non-current, Balance at End of Period	$ 3,333	$ 600	$ 3,333	$ 600

License and Royalty Revenue -_2

License and Royalty Revenue - Additional Information (Detail1)	Sep. 30, 2019
January 2018 Amendment Agreement [Member] | AveXis, Inc. [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2018-01-01
License Revenue [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, period	1 year

License and Royalty Revenue -_3

License and Royalty Revenue - Schedule Of License Revenue (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
License Revenue [Line Items]
Total license and royalty revenue	$ 9,182	$ 4,000	$ 13,606	$ 176,066
Interest income from licensing	716	109	2,091	8,362
AveXis, Inc. [Member]
License Revenue [Line Items]
Interest income from licensing	7	8	22	7,958
License [Member]
License Revenue [Line Items]
Total license and royalty revenue		$ 4,000	3,500	$ 176,066
Zolgensma Royalties [Member]
License Revenue [Line Items]
Total license and royalty revenue	$ 9,182		$ 10,106

Stock-based Compensation - Addi

Stock-based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	9 Months Ended
	Jan. 31, 2019	Sep. 30, 2019	Sep. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation expense		$ 67,700
Unrecognized stock-based compensation, weighted-average period		2 years 9 months 18 days
Proceeds from exercise of stock options		$ 5,513	$ 9,051
2015 Equity Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Additional shares to be issued	1,444,808
Common stock shares authorized for issuance		10,933,221
Shares available for future grants		2,189,562
Weighted-average fair values of options granted		$ 31.84
Exercise of stock options, Shares		684,218
Total intrinsic value of options exercised		$ 27,800
2015 Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares authorized for issuance		254,000
Shares available for future grants		133,586
Common stock shares issued to participants		35,994

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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 7,162	$ 4,483	$ 19,979	$ 11,755
Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	6,965	4,309	19,261	11,248
Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	69	69	206	206
Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 128	$ 105	$ 512	$ 301

Stock-based Compensation - St_2

Stock-based Compensation - Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 7,162	$ 4,483	$ 19,979	$ 11,755
Research and Development Costs [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	3,657	1,940	9,530	5,364
General and Administrative [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 3,505	$ 2,543	$ 10,449	$ 6,391

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, 2019USD ($)$ / sharesshares	Dec. 31, 2018USD ($)$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares [Roll Forward]
Shares Outstanding, Beginning Balance | shares	4,855
Shares, Granted | shares	1,596
Shares, Exercised | shares	(684)
Shares, Cancelled or forfeited | shares	(237)
Shares Outstanding, Ending Balance | shares	5,530	4,855
Shares, Exercisable | shares	2,827
Shares, Vested and expected to vest | shares	5,530
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted-average Exercise Price Outstanding, Beginning Balance | $ / shares	$ 19.31
Weighted-average Exercise Price, Granted | $ / shares	47.82
Weighted-average Exercise Price, Exercised | $ / shares	8.07
Weighted-average Exercise Price, Cancelled or forfeited | $ / shares	33.74
Weighted-average Exercise Price, Outstanding, Ending Balance | $ / shares	28.31	$ 19.31
Weighted-average Exercise Price, Exercisable | $ / shares	15.48
Weighted-average Exercise Price, Vested and expected to vest | $ / shares	$ 28.31
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted-average Remaining Contractual Life (Years) Outstanding	7 years 8 months 12 days	7 years 7 months 6 days
Weighted-average Remaining Contractual Life (Years), Exercisable	6 years 7 months 6 days
Weighted-average Remaining Contractual Life (Years), Vested and expected to vest	7 years 8 months 12 days
Aggregate Intrinsic Value Outstanding | $	$ 69,769	$ 118,185
Aggregate Intrinsic Value, Exercisable | $	60,340
Aggregate Intrinsic Value, Vested and expected to vest | $	$ 69,769

Stock-based Compensation - Su_2

Stock-based Compensation - Summary of Unvested RSUs Activity Under 2015 Plan (Detail) - Restricted Stock Units [Member] shares in Thousands	9 Months Ended
	Sep. 30, 2019$ / sharesshares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares Unvested, Beginning Balance	40
Shares, Granted	0
Shares, Vested	0
Shares, Forfeited	0
Shares Unvested, Ending Balance	40
Weighted-average Grant Date Fair Value, Unvested Beginning Balance | $ / shares	$ 20.90
Weighted-average Grant Date Fair Value, Unvested Ending Balance | $ / shares	$ 20.90

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Income Tax Disclosure [Line Items]
Income tax benefit	$ 165	$ 1,292	$ 364	$ (2,558)
Unrealized gains (losses) on available-for-sale debt securities, income tax benefit (expense)	100	$ 0	(600)	$ 0
Accrued income tax provision	508		508		$ 726
Accrued Expenses and Other Current Liabilities [Member]
Income Tax Disclosure [Line Items]
Accrued income tax provision	$ 300		$ 300

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
FOXKISER,LLP [Member] | Service Agreements [Member] | Research and Development Costs [Member]
Related Party Transaction [Line Items]
Related party transaction expense	$ 1.2	$ 0.5	$ 2.9	$ 1.6

Net Income (Loss) Per Share - C

Net Income (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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Basic net income (loss) per share:
Net income (loss) applicable to common stockholders	$ (34,584)	$ (19,202)	$ (68,269)	$ 95,631
Shares used in computation:
Weighted-average common shares outstanding	36,813	33,988	36,618	32,576
Basic net income (loss) per share	$ (0.94)	$ (0.56)	$ (1.86)	$ 2.94
Diluted net income (loss) per share:
Net income (loss) applicable to common stockholders	$ (34,584)	$ (19,202)	$ (68,269)	$ 95,631
Shares used in computation:
Weighted-average common shares outstanding	36,813	33,988	36,618	32,576
Weighted-average diluted common shares	36,813	33,988	36,618	35,875
Diluted net income (loss) per share	$ (0.94)	$ (0.56)	$ (1.86)	$ 2.67
Stock Option [Member]
Shares used in computation:
Weighted-average diluted common shares				3,268
Restricted Stock Units [Member]
Shares used in computation:
Weighted-average diluted common shares				31

Net Income (Loss) Per Share - S

Net Income (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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted weighted average shares outstanding	5,586	5,215	5,586	1,132
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	5,530	5,171	5,530	1,128
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	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	4	16	4

Supplemental Disclosures - Sche

Supplemental Disclosures - Schedules of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
Accrued personnel costs	$ 8,869	$ 9,484
Accrued external research and development expenses	4,390	4,274
Accrued sublicense fees and royalties	3,245	1,617
Accrued external general and administrative expenses	1,137	773
Accrued income taxes payable	508	726
Accrued purchases of property and equipment	349	221
Other accrued expenses and current liabilities	733	69
Accrued expenses and other current liabilities	$ 19,231	$ 17,164

Supplemental Disclosures - Addi

Supplemental Disclosures - Additional Information (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
Other liabilities	$ 1,844	$ 2,505