REGENXBIO (RGNX) 10-K 27 Feb 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2018	Feb. 22, 2019	Jun. 30, 2018
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Trading Symbol	RGNX
Entity Registrant Name	REGENXBIO Inc.
Entity Central Index Key	1,590,877
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		36,418,716
Entity Public Float			$ 1,624,447,767

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets
Cash and cash equivalents	$ 75,561	$ 46,656
Marketable securities	244,200	114,122
Accounts receivable	8,587	473
Prepaid expenses	5,734	5,334
Other current assets	3,831	1,412
Total current assets	337,913	167,997
Marketable securities	150,819	15,616
Accounts receivable	23,012
Property and equipment, net	28,702	13,977
Restricted cash	1,053	225
Other assets	2,315	862
Total assets	543,814	198,677
Current liabilities
Accounts payable	4,412	4,832
Accrued expenses and other current liabilities	17,164	9,605
Deferred revenue	600
Total current liabilities	22,176	14,437
Deferred revenue	3,333
Deferred rent, net of current portion	1,098	1,211
Financing lease obligation	5,854
Other liabilities	2,505
Total liabilities	34,966	15,648
Commitments and contingencies (Note 6)
Stockholders’ equity
Preferred stock; $0.0001 par value; 10,000 shares authorized, and no shares issued and outstanding at December 31, 2018 and December 31, 2017
Common stock; $0.0001 par value; 100,000 shares authorized at December 31, 2018 and December 31, 2017; 36,120 and 31,295 shares issued and outstanding at December 31, 2018 and December 31, 2017, respectively	4	3
Additional paid-in capital	592,580	371,497
Accumulated other comprehensive loss	(720)	(715)
Accumulated deficit	(83,016)	(187,756)
Total stockholders’ equity	508,848	183,029
Total liabilities and stockholders’ equity	$ 543,814	$ 198,677

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
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	36,120,000	31,295,000
Common stock, shares outstanding	36,120,000	31,295,000

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues
Revenues	$ 218,505	$ 10,393	$ 4,589
Costs of revenues
Research and development	83,873	57,224	45,482
General and administrative	36,850	27,229	23,590
Other operating expenses (income)	42	116	(102)
Total operating expenses	130,405	86,278	69,929
Income (loss) from operations	88,100	(75,885)	(65,340)
Other Income
Interest income from licensing	8,946
Investment income	7,070	2,716	1,938
Total other income	16,016	2,716	1,938
Income (loss) before income taxes	104,116	(73,169)	(63,402)
Income Tax Benefit (Expense)	(4,179)	0	435
Net income (loss)	99,937	(73,169)	(62,967)
Other Comprehensive Income (Loss)
Unrealized gain (loss) on available-for-sale securities, net of reclassifications and income tax expense	(5)	(682)	686
Total other comprehensive income (loss)	(5)	(682)	686
Comprehensive income (loss)	99,932	(73,851)	(62,281)
Net income (loss) applicable to common stockholders	$ 99,937	$ (73,169)	$ (62,967)
Net income (loss) per share:
Basic	$ 2.99	$ (2.45)	$ (2.38)
Diluted	$ 2.73	$ (2.45)	$ (2.38)
Weighted-average common shares outstanding:
Basic	33,427	29,878	26,409
Diluted	36,648	29,878	26,409
License [Member]
Revenues
Revenues	$ 218,505	$ 10,385	$ 4,303
Costs of revenues
Costs of revenues	$ 9,640	1,703	861
Other [Member]
Revenues
Revenues		8	286
Costs of revenues
Costs of revenues		$ 6	$ 98

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 Loss [Member]	Accumulated Deficit [Member]
Balances at Dec. 31, 2015	$ 216,808	$ 3	$ 269,144	$ (719)	$ (51,620)
Balances (Shares) at Dec. 31, 2015		26,313
Exercise of stock options	179		179
Exercise of stock options, Shares		163
Stock-based compensation expense	7,031		7,031
Unrealized gain (loss) on available-for-sale securities, net of reclassifications and income tax expense	686			686
Net income (loss)	(62,967)				(62,967)
Balances at Dec. 31, 2016	161,737	$ 3	276,354	(33)	(114,587)
Balances (Shares) at Dec. 31, 2016		26,477
Issuance of common stock upon public offering, net of transaction costs	81,489		81,489
Issuance of common stock upon public offering, net of transaction costs, Shares		4,255
Exercise of stock options	2,493		2,493
Exercise of stock options, Shares		516
Issuance of common stock under employee stock purchase plan	556		556
Issuance of common stock under employee stock purchase plan, shares		48
Stock-based compensation expense	10,605		10,605
Unrealized gain (loss) on available-for-sale securities, net of reclassifications and income tax expense	(682)			(682)
Net income (loss)	(73,169)				(73,169)
Balances at Dec. 31, 2017	183,029	$ 3	371,497	(715)	(187,756)
Balances (Shares) at Dec. 31, 2017		31,295
Adoption of ASC 606	4,803				4,803
Issuance of common stock upon public offering, net of transaction costs	189,097	$ 1	189,096
Issuance of common stock upon public offering, net of transaction costs, Shares		3,105
Exercise of stock options	14,499		14,499
Exercise of stock options, Shares		1,683
Issuance of common stock under employee stock purchase plan	847		847
Issuance of common stock under employee stock purchase plan, shares		37
Stock-based compensation expense	16,641		16,641
Unrealized gain (loss) on available-for-sale securities, net of reclassifications and income tax expense	(5)			(5)
Net income (loss)	99,937				99,937
Balances at Dec. 31, 2018	$ 508,848	$ 4	$ 592,580	$ (720)	$ (83,016)
Balances (Shares) at Dec. 31, 2018		36,120

Consolidated Statements of St_2

Consolidated Statements of Stockholders' Equity (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Common Stock [Member]
Issuance of Stock, transaction costs	$ 12,728	$ 5,738

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities
Net income (loss)	$ 99,937	$ (73,169)	$ (62,967)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities
Stock-based compensation expense	16,641	10,605	7,031
Net amortization of premiums and accretion of discounts on marketable debt securities	755	1,815	2,004
Depreciation and amortization	3,982	2,686	544
Net realized losses (gains) on sales and maturities of marketable securities	39	(479)
Imputed interest income from licensing	(8,946)
Non-cash consideration received for licenses granted		(420)
Other non-cash adjustments	14	73	(399)
Changes in operating assets and liabilities
Accounts receivable	(16,803)	561	1,073
Prepaid expenses	(400)	(3,559)	(755)
Other current assets	(2,069)	(402)	(159)
Other assets	(1,453)	(135)	(139)
Accounts payable	(218)	2,621	186
Accrued expenses and other current liabilities	7,582	1,897	3,873
Deferred revenue	3,933
Advance payments			(127)
Deferred rent	(32)	(86)	1,277
Other liabilities	1,686
Net cash provided by (used in) operating activities	104,648	(57,992)	(48,558)
Cash flows from investing activities
Purchases of marketable securities	(445,829)	(68,634)	(45,072)
Maturities of marketable securities	179,749	70,224	72,586
Sales of marketable securities		780	23
Purchases of property and equipment	(13,278)	(7,160)	(8,149)
Net cash provided by (used) in investing activities	(279,358)	(4,790)	19,388
Cash flows from financing activities
Proceeds from exercise of stock options	14,499	2,493	179
Proceeds from issuance of common stock under employee stock purchase plan	847	556
Proceeds from public offerings of common stock, net of underwriting discounts and commissions	189,716	81,994
Issuance costs for public offerings of common stock	(619)	(445)	(60)
Net cash provided by financing activities	204,443	84,598	119
Net increase (decrease) in cash and cash equivalents and restricted cash	29,733	21,816	(29,051)
Cash and cash equivalents and restricted cash
Beginning of period	46,881	25,065	54,116
End of period	76,614	46,881	25,065
Supplemental cash flow information
Cash paid for income taxes	3,443
Supplemental disclosures of non-cash investing and financing activities
Purchases of property and equipment in accounts payable and accrued expenses		254	1,181
Assets acquired under financing lease obligation	$ 5,854
Non-cash consideration received for licenses granted		$ 420
Issuance costs for public offerings of common stock in accounts payable and accrued expenses			$ 33

Nature of Business

Nature of Business	12 Months Ended
	Dec. 31, 2018
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 product candidates for a variety of diseases with unmet needs. The Company was formed in 2008 in the State of Delaware and is headquartered in Rockville, Maryland. Liquidity and Risks As of December 31, 2018, the Company had generated an accumulated deficit of $83.0 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 December 31, 2018, the Company had cash, cash equivalents and marketable securities of $470.6 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	12 Months Ended
	Dec. 31, 2018
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 have been prepared in conformity with accounting principles generally accepted in the United States of America (GAAP). 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. Foreign Currency Transactions The functional currency of the Company and its consolidated subsidiaries is the U.S. dollar. Transaction gains and losses that arise from exchange rate fluctuations on transactions denominated in a currency other than the U.S. dollar are included in results of operations as incurred. 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: 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. Segment and Geographical Information Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision maker (CODM), or decision-making group, in making decisions on how to allocate resources and assess performance. The Company’s CODM, the Chief Executive Officer, views its operations and manages its business as one operating segment. The Company’s revenue primarily consists of license revenue. For the year ended December 31, 2018, 99% of the Company’s revenue was generated from customers located in the U.S. For the year ended December 31, 2017, 96% of the Company’s revenue was generated from customers located in the U.S. For the year ended December 31, 2016, 90% of the Company’s revenue was generated from customers located in the U.S. Country of origin for license revenue is determined based on the country of domicile of the licensee. The substantial majority of the Company’s assets currently reside in the U.S. Cash and Cash Equivalents The Company considers all highly liquid investments purchased with original maturities of 90 days or less at acquisition to be cash equivalents. 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): December 31, 2018 December 31, 2017 December 31, 2016 Cash and cash equivalents $ 75,561 $ 46,656 $ 24,840 Restricted cash 1,053 225 225 Total cash and cash equivalents and restricted cash $ 76,614 $ 46,881 $ 25,065 Marketable Securities Marketable securities consist of debt securities and are classified as available-for-sale and carried at fair value. Marketable 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. Unrealized gains and losses, 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. Purchase premiums and discounts 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. 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. A decline in the fair value below cost of available-for-sale 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 investments below their cost are other-than-temporary. The evaluation includes consideration of the cause of the impairment, including the creditworthiness of the security issuers, the number of securities in an unrealized loss position, the severity and duration of the unrealized losses, whether the Company has the intent to sell the securities and whether it is more likely than not that the Company will be required to sell the securities before the recovery of their amortized cost basis. The Company has not recorded any impairment of available-for-sale securities which was deemed to be to be other-than-temporary. Concentrations of Credit Risk and Off-balance Sheet Risk Cash and cash equivalents, marketable securities and accounts receivable are financial instruments that are potentially subject to concentrations of credit risk. The Company’s cash and cash equivalents are deposited in accounts at multiple financial institutions, and amounts may exceed federally insured limits. The Company believes it is not exposed to significant credit risk due to the financial strength of the depository institutions in which the cash and cash equivalents are held. The Company’s marketable securities consist of investment grade debt securities and may be subject to concentrations of credit risk. The Company has adopted an investment policy which limits potential concentrations of investments and establishes minimum acceptable credit ratings, thereby reducing credit risk exposure. 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. The Company has no financial instruments with off-balance sheet risk of loss. The following table summarizes those customers who represented at least 10% of revenue or accounts receivable, current and non-current, for the periods presented: Revenue Accounts Receivable Years Ended December 31, December 31, 2018 2017 2016 2018 2017 Customer A 81 % 68 % * * * Customer B 16 % * * 82 % * Customer C * * 24 % * * Customer D * * * * 42 % Customer E * * * * 32 % Customer F * * 44 % * * Customer G * * * * 21 % * Represented less than 10% Accounts Receivable Accounts receivable primarily consist of consideration due to the Company resulting from its license agreements with NAV Technology Licensees. Accounts receivable include amounts invoiced to licensees as well as rights to consideration which have not yet been invoiced and for which payment is conditional solely upon the passage of time. If a licensee elects to terminate a license prior to the end of the license term, the licensed intellectual property is returned to the Company and any accounts receivable from the licensee which are not contractually payable to the Company are charged off as a reduction of license revenue in the period of the termination. Accounts receivable which are not expected to be received by the Company within 12 months from the reporting date are stated net of a discount to present value and recorded as non-current assets on the consolidated balance sheets. The present value discount is recognized as a reduction of revenue in the period in which the accounts receivable are initially recorded and is accreted as interest income from licensing over the term of the receivables. Accounts receivable are stated net of an allowance for doubtful accounts, if deemed necessary based on the Company’s evaluation of collectability using specific identification of account balances, the credit profile and financial condition of its customers and historical information regarding write-offs. Account balances are charged off against the allowance when the potential for recovery is considered remote. The Company did not record an allowance for doubtful accounts as of December 31, 2018 or 2017. Property and Equipment Property and equipment is stated at cost less accumulated depreciation and amortization. Maintenance and repairs that do not improve or extend the lives of the respective assets are expensed to operations as incurred. Upon disposal, the related cost and accumulated depreciation is removed from the accounts and any resulting gain or loss is included in the results of operations. Depreciation and amortization is calculated using the straight-line method over the estimated useful lives of the assets, which are as follows: Computer equipment and software 3 years Lab equipment 5 years Furniture and fixtures 5 years Leasehold improvements Shorter of lease term or estimated useful life Certain estimated construction costs incurred and reported by the Company’s landlord at 9800 Medical Center Drive are recorded as property and equipment, with a corresponding financing lease obligation, on the consolidated balance sheets. Please refer to Note 6 for further information on the Company’s lease agreements. Impairment of Long-lived Assets The Company reviews long-lived assets when events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Recoverability is measured by comparison of the book values of the assets to estimated future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the book value of the assets exceed their fair value, which is measured based on the projected discounted future net cash flows arising from the assets. No impairment losses have been recorded during the years ended December 31, 2018, 2017 and 2016. Non-marketable Equity Securities The Company’s non-marketable equity securities do not have readily determinable fair values and consist of equity investments in other entities in which the Company’s ownership interest is below 20% and the Company does not have significant influence over the operations of the entity. Prior to January 1, 2018, non-marketable equity securities were accounted for using the cost method and measured at cost less impairment. Beginning January 1, 2018, upon the Company’s adoption of Accounting Standards Update (ASU) 2016-01, Financial Instruments—Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities Declines in the fair value of non-marketable equity securities below their carrying values that are deemed to be other-than-temporary are charged to results of operations as realized losses. In estimating other-than-temporary impairment losses, management considers, among other things, the length of time and the extent to which the fair value has been less than cost, the financial condition and near-term prospects of the issuer and the intent and ability of the Company to retain its investments in the issuer for a period of time sufficient to allow for the anticipated recovery in fair value. The Company has not recorded any other-than-temporary impairment losses on its non-marketable equity securities. Fair Value of Financial Instruments The Company is required to disclose information on all assets and liabilities reported at fair value that enables an assessment of the inputs used in determining the reported fair values. Accounting Standards Codification (ASC) Topic 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 Effective January 1, 2018, the Company adopted ASU 2014-09, Revenue from Contracts with Customers Revenue Recognition Topic 606 requires entities to recognize revenue when control of the promised goods or services is transferred to customers at an amount that reflects the consideration to which the entity expects to be entitled to in exchange for those goods or services. The following five steps are performed to determine the appropriate revenue recognition for arrangements within the scope of Topic 606: (i) identify the contract(s) with a customer, (ii) identify the performance obligations in the contract, (iii) determine the transaction price, (iv) allocate the transaction price to the performance obligations in the contract and (v) recognize revenue when (or as) the entity satisfies the performance obligations. 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 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 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. 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 in the consolidated statements of operations 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. To date the Company has not recognized any revenue from royalties on sales of licensed products or the achievement of sales-based milestones. 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 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. Other Revenues Other revenues consist of sales of licensed reagents to third parties for use in research and development and grant revenue generated through research and development grant programs offered by the European Union. Revenue from reagent sales is recognized when control of the licensed reagents is transferred to the customer. Grant revenue is recognized in the period in which the related costs are incurred and the related services are rendered by the Company. As of December 31, 2017, all grant programs were completed. Costs of Revenues Licensing costs consist of sublicense fees to licensors as a result of license revenues generated by the Company. Sublicense fees are based on a percentage of license fees received by the Company from licensees as specified in the Company’s agreements with its licensors. The Company recognizes sublicense fees in the period that the underlying license revenue is recognized. Sublicense fees payable by the Company to licensors in periods beyond 12 months from the reporting date are recorded as non-current liabilities on the consolidated balance sheets. Other costs of revenue consist of royalties to licensors as a result of the sales of licensed reagents by the Company. The Company recognizes royalties on sales of licensed reagents in the period that the underlying sales occur. Research and Development Expenses Research and development costs are expensed as incurred. Advance payments for goods or services related to research and development activities are deferred and expensed as the goods are delivered or the related services are performed. Research and development costs include salaries, benefits and other personnel costs, laboratory and facilities costs and other overhead costs allocated to research and development activities. Additionally, research and development costs include goods and services associated with preclinical research, clinical trial activities, manufacturing-related activities, regulatory and other related services performed by third-parties. At the end of each reporting period, the Company compares payments made to third-party service providers to the estimated expenses incurred based on the services provided and progress toward completion of the research or development objectives. Such estimates are subject to change as additional information becomes available. Depending on the timing of payments to the service providers and the estimated expenses incurred, the Company may record net prepaid or accrued research and development expenses relating to these costs. Up-front fees incurred in obtaining technology licenses, as well as milestone payments to licensors, are charged to research and development expense as incurred if the technology licensed has no alternative future use. Stock-based Compensation The Company accounts for its stock-based compensation awards in accordance with ASC 718, Compensation—Stock Compensation The Company’s stock-based awards are subject to either service or performance-based vesting conditions. Compensation expense related to awards to employees and nonemployees with service-based vesting conditions is recognized on a straight-line basis based on the estimated grant date fair value over the requisite service period of the award, which is generally the vesting term. Compensation expense related to awards to employees and nonemployees with performance-based vesting conditions is recognized based on the estimated grant date fair value over the requisite service period using the accelerated attribution method to the extent achievement of the performance condition is probable. The Company estimates the fair value of its stock option awards using the Black-Scholes option-pricing model, which requires the input of subjective assumptions, including (i) the fair value of the underlying common stock, (ii) the expected stock price volatility, (iii) the expected term of the award, (iv) the risk-free interest rate and (v) expected dividends. The Company does not have sufficient historical and implied volatility data for its common stock necessary to estimate the expected the volatility of its common stock over a period of time commensurate with the expected term of its stock option awards. As a result, the Company estimates expected volatility based on the historical volatility of both its common stock and the common stock of a selected peer group of similar publicly traded companies for which sufficient historical volatility data is available. Due to the lack of historical volatility data for its common stock, the Company places a higher weight on the historical volatility of the selected peer group in estimating expected volatility. The Company computes the historical volatility data using the daily closing prices for the selected companies’ shares during a period equivalent to the expected term of the stock option awards. For the purpose of identifying the selected peer group companies, the Company considers characteristics such as enterprise value, risk profiles, position within the industry and length of historical share price information. The Company plans to continue using historical peer group volatility data as an input to estimate expected volatility until a sufficient amount of historical volatility data for its common stock becomes available. The Company estimates the expected term of its employee stock options using the “simplified” method, whereby, the expected term equals the arithmetic average of the vesting term and the original contractual term of the option due to its lack of sufficient historical data. For stock options granted to nonemployees, the Company uses the contractual term of the award rather than expected term to estimate the fair value of the award. The Company estimates the risk-free interest rates for periods within the expected term of its options based on the rates of U.S. Treasury securities with maturity dates commensurate with the expected term of the associated awards. The Company has never paid and does not expect to pay dividends in the foreseeable future. The Company estimates the fair value of restricted stock units based on the fair value of the Company’s common stock on the date of the grant. On July 1, 2018, the Company adopted ASU 2018-07, Compensation—Stock Compensation (Topic 718): Improvements to Nonemployee Share-based Payment Accounting For the year ended December 31, 2016, the Company was also required to estimate forfeitures of stock-based awards at the time of grant and revise those estimates in subsequent periods if actual forfeitures differ from its estimates. For all periods through December 31, 2016, a forfeiture rate of zero was used to calculate stock-based compensation exp

Marketable Securities

Marketable Securities	12 Months Ended
	Dec. 31, 2018
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 solely of available-for-sale debt securities (in thousands): 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 Amortized Cost Unrealized Gains Unrealized Losses Fair Value December 31, 2017 Corporate bonds $ 130,018 $ 2 $ (282 ) $ 129,738 $ 130,018 $ 2 $ (282 ) $ 129,738 As of December 31, 2018 and 2017, no marketable securities had remaining maturities greater than three years. The amortized cost of available-for-sale securities is adjusted for amortization of premiums and accretion of discounts to maturity. As of December 31, 2018 and 2017, the balance in the Company’s accumulated other comprehensive loss consisted solely of net unrealized gains and losses on available-for-sale securities, net of income tax effects and reclassification adjustments for realized gains and losses. During the years ended December 31, 2018, 2017 and 2016, the Company recognized net unrealized gains (losses) on available-for-sale securities of less than $(0.1) million, $(0.2) million and $1.1 million, respectively, and income tax expense of zero, zero and $0.4 million, respectively, in other comprehensive income (loss). The Company recognized net realized gains (losses) of less than $(0.1) million, $0.5 million and less than $(0.1) million on the sale or maturity of available-for-sale securities during the years ended December 31, 2018, 2017 and 2016, respectively, which were reclassified out of accumulated other comprehensive loss during the period and are included in investment income in the consolidated statements of operations and comprehensive income (loss). The following tables present the 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 (in thousands): 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 ) Less than 12 Months 12 Months or Greater Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses December 31, 2017 Corporate bonds $ 109,238 $ (180 ) $ 17,124 $ (102 ) $ 126,362 $ (282 ) $ 109,238 $ (180 ) $ 17,124 $ (102 ) $ 126,362 $ (282 ) As of December 31, 2018, marketable securities held by the Company which were in an unrealized loss position consisted of 102 investment grade security positions. The Company has the intent and ability to hold such securities until recovery and has determined that none of its investments were other-than-temporarily impaired as of December 31, 2018 or 2017.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	12 Months Ended
	Dec. 31, 2018
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 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 Quoted Significant prices other Significant in active observable unobservable markets inputs inputs (Level 1) (Level 2) (Level 3) Total December 31, 2017 Cash equivalents: Money market mutual funds $ — $ 46,646 $ — $ 46,646 Total cash equivalents — 46,646 — 46,646 Marketable securities: Corporate bonds — 129,738 — 129,738 Total marketable securities — 129,738 — 129,738 Total cash equivalents and marketable securities $ — $ 176,384 $ — $ 176,384 There were no transfers of financial instruments between levels of the fair value hierarchy during the years ended December 31, 2018 and 2017. 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 December 31, 2018 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. The Company’s 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 and 2017, non-marketable equity securities had carrying values of $0.4 million and are included in other assets on the consolidated balance sheets. Since the acquisition of the securities, the Company has not identified any observable price changes or changes in circumstances that would have an adverse effect on the fair value of the securities as of December 31, 2018 and 2017. No remeasurements or impairment losses were recorded on non-marketable equity securities during the years ended December 31, 2018, 2017 and 2016.

Property and Equipment, Net

Property and Equipment, Net	12 Months Ended
	Dec. 31, 2018
Property Plant And Equipment [Abstract]
Property and Equipment, Net	5. Property and Equipment, Net Property and equipment, net consists of the following (in thousands): December 31, 2018 December 31, 2017 Lab equipment $ 14,417 $ 8,561 Computer equipment and software 2,002 1,481 Furniture and fixtures 1,915 1,384 Leasehold improvements 11,751 5,828 Construction-in-progress 5,854 — Total property and equipment 35,939 17,254 Accumulated depreciation and amortization (7,237 ) (3,277 ) Property and equipment, net $ 28,702 $ 13,977 Construction-in-progress in the table above consists of certain costs incurred and reported by the Company’s landlord at 9800 Medical Center Drive. Please refer to Note 6 for further information on the Company’s lease agreements. Construction costs incurred by the Company for the building at 9800 Medical Center Drive were less than $0.1 million as of December 31, 2018. During the years ended December 31, 2018, 2017 and 2016, the Company recorded depreciation expense of $4.0 million ,

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2018
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	6. Commitments and Contingencies Lease Commitments The Company recognizes rent expense on a straight-line basis over the term of its operating leases commencing on the date the Company takes possession of the leased property. Tenant improvement allowances that are considered to be lease incentives from the lessor are recorded as deferred rent and amortized as a reduction of rent expense over the term of the lease from the possession date. 9800 Medical Center Drive Lease In November 2018, the Company entered into a lease for approximately 132,000 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). Construction of the new building, which will be conducted by the landlord, is expected to be completed in 2020 and the lease will expire approximately 16 years from the delivery of the leased premises to the Company, subject to certain extension and termination options. Under the terms of the 9800 Medical Center Drive Lease, the Company will receive a $14.6 million tenant improvement allowance from the landlord to construct additional improvements to the leased premises. 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 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. Accordingly, for accounting purposes only, the Company is deemed the owner of the leased premises during the construction period. Certain estimated construction costs incurred and reported by the landlord are recorded as property and equipment, with a corresponding financing lease obligation, on the consolidated balance sheets. The portion of the lease allocated to the land on which the building is located is treated for accounting purposes as an operating lease that commenced upon the execution of the 9800 Medical Center Drive Lease in November 2018. Imputed rent expense attributable to the land portion of the lease was not material for the year ended December 31, 2018. Other Lease Commitments In March 2015, the Company entered into a non-cancelable 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. Under the amended lease, the Company has received a $0.4 million tenant improvement allowance from the landlord which will be deferred and 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 a 7.5-year, non-cancelable operating lease for its corporate headquarters at 9600 Blackwell Road in Rockville, Maryland (the Blackwell Road Lease). The lease commenced in February 2016, and expires in September 2023. The Company has an option to extend the term of the lease for an additional five years. 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 received a $0.8 million tenant improvement allowance from the landlord which will be deferred and amortized on a straight-line basis as a reduction of rent expense over the term of lease. The Company leases additional office and laboratory facilities in Rockville, Maryland and New York, New York, as well as laboratory and other equipment, under non-cancelable operating leases with various expiration dates through 2021 and which may contain annual escalations of rental payments. As required by the Company’s lease agreement for its office space in New York, New York, 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. As of December 31, 2018, future minimum lease payments under 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 sheets. The actual timing and amounts of payments under the lease are subject to adjustment based on the completion date of construction and actual square footage of the facility. Rent expense under all leases, including additional rent charges for utilities, parking, property management, operating expenses and real estate taxes for the years ended December 31, 2018, 2017 and 2016 was $2.8 million, $1.8 million and $1.8 million, respectively. Licenses Granted to the Company The Company licenses intellectual property from third-parties, primarily for technology used in the Company’s product candidates and development programs and which may be sublicensed to NAV Technology Licensees. Licenses granted to the Company may require the Company to make future payments relating to sublicense fees, milestone fees and royalties on future sales of licensed products. Additionally, the Company may be responsible for the cost of the maintenance of the intellectual property as incurred by its licensors. Up-front fees to obtain licensed technology are included in research and development expenses and patent maintenance costs are included in general and administrative expenses in the consolidated statements of operations and comprehensive income (loss). Sublicense fees are based on a specified percentage of license fees earned by the Company and are included in licensing costs in the consolidated statements of operations and comprehensive income (loss). Milestone fees are included in licensing costs in the consolidated statements of operations and comprehensive income (loss) if the underlying milestone is achieved by a licensee, or in research and development expense if the underlying milestone is achieved by the Company as a result of the development of its product candidates. Royalties on sales of licensed reagents for use in research and development are included in other costs of revenue in the consolidated statements of operations and comprehensive income (loss). The Company has not commercialized any product candidates or paid any royalties under these agreements other than for the sales of licensed reagents. 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). In consideration for the license, the Company issued Penn an equity interest in 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. Expenses incurred by the Company related to its license from Penn were recorded as follows (in thousands): Years Ended December 31, 2018 2017 2016 Licensing costs $ (18 ) $ 207 $ 430 Other costs of revenue — 4 11 General and administrative 130 233 133 $ 112 $ 444 $ 574 As of December 31, 2018 and 2017, the Company had accrued $0.1 million and less than $0.1 million, respectively, in expenses payable to Penn under the license agreement, which are included in accounts payable, accrued expenses and other current liabilities and other liabilities on the consolidated balance sheets. GlaxoSmithKline LLC In March 2009, the Company entered into a license agreement, which was amended in April 2009, with GlaxoSmithKline LLC (GSK) for exclusive, worldwide rights to certain patents underlying the Company’s NAV Technology Platform which are owned by Penn and exclusively licensed to GSK. In consideration for the license the Company issued GSK an equity interest in the Company and is obligated to pay GSK royalties on net sales of licensed products and sublicense fees. Additionally, the Company is obligated to reimburse GSK for certain costs incurred related to the maintenance of the licensed patents. The Company is also obligated to pay GSK up to $1.5 million upon the achievement of various milestones. From the inception of the agreement through December 31, 2018, the Company has paid or accrued $0.5 million to GSK for milestones that have been achieved or are deemed probable of achievement. Expenses incurred by the Company related to its license from GSK were recorded as follows (in thousands): Years Ended December 31, 2018 2017 2016 Licensing costs $ 9,407 $ 1,497 $ 430 Other costs of revenue — 2 7 General and administrative 548 509 597 $ 9,955 $ 2,008 $ 1,034 As of December 31, 2018 and 2017, the Company had accrued $4.1 million and $0.3 million, respectively, in expenses payable to GSK under the license agreement, which are included in accounts payable, accrued expenses and other current liabilities and other liabilities on the consolidated balance sheets. Other Licenses In November 2014, the Company entered into a license agreement, which was amended in November 2016, with Regents of the University of Minnesota (Minnesota), for an exclusive license under Minnesota’s interest in certain patent rights which are co-owned by Minnesota and the Company to commercialize products covered by the licensed patent rights in any country or territory in which a licensed patent has been issued and is unexpired, or a licensed patent application is pending. In consideration for the license, the Company paid an up-front fee, and reimbursed Minnesota for patent maintenance expenses incurred to date. Under the terms of the agreement, the Company is obligated to pay Minnesota an upfront fee, annual maintenance fees, royalties on net sales, sublicense fees and fees upon the achievement of various milestones. In November 2016, the license with Minnesota was amended to include additional patent rights. In consideration for the additional patent rights, the Company paid an up-front fee. In August 2018, the Company entered into a license agreement with Emory University (Emory) for an exclusive license under Emory’s interest in certain patent rights which are co-owned by Emory and the Company to commercialize products covered by the licensed patent rights in any country or territory. In consideration for the license, the Company paid an up-front fee and is obligated to reimburse Emory for patent prosecution and maintenance expenses and pay Emory annual maintenance fees under certain circumstances, royalties on net sales, sublicense fees and fees upon the achievement of various milestones for the first licensed product. Other Funding Commitments In the normal course of business, the Company enters into agreements with contract research organizations, contract manufacturing organizations and other third-parties for services to be provided to the Company. Generally, these agreements provide for termination upon notice, with specified amounts due upon termination based on the timing of termination and the terms of the agreement. The actual amounts and timing of payments under these agreements are uncertain and contingent upon the initiation and completion of services to be provided to the Company. Guarantees and Indemnifications In the normal course of business, the Company enters into agreements that contain a variety of representations and provide for general indemnification. The Company’s potential exposure under these agreements is unknown because it involves claims that may be made against the Company in the future. To date, the Company has not paid any claims or been required to defend any action related to its indemnification obligations. As of December 31, 2018 and 2017, the Company did not have any material indemnification claims that were probable or reasonably possible and consequently has not recorded any related liabilities. 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 December 31, 2018 and 2017, the Company has not recorded any liabilities related to this matter.

Capitalization

Capitalization	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Capitalization	7. Capitalization As of December 31, 2018 and 2017, the authorized capital stock of the Company included 100,000,000 shares of common stock, par value $0.0001 per share, and 10,000,000 shares of preferred stock, par value $0.0001 per share. The Company’s restated certificate of incorporation and bylaws contain the rights, preferences and privileges of the Company’s stockholders and their respective shares. In March 2017, the Company completed a public offering of 3,700,000 shares of its common stock at a price of $20.50 per share. In connection with the offering, the Company granted the underwriters an option to purchase 555,000 additional shares of common stock at the public offering price. The underwriters exercised the option in full and purchased the additional shares in April 2017. The aggregate net proceeds received by the Company from the offering, inclusive of the underwriters’ option exercise, were $81.5 million, net of underwriting discounts and commissions and offering expenses payable by the Company. In August 2018, the Company completed a public offering of 3,105,000 shares of its common stock (inclusive of 405,000 shares pursuant to the full exercise by the underwriters of their option to purchase additional shares) at a price of $65.00 per share. The aggregate net proceeds received by the Company from the offering, inclusive of the underwriters’ option exercise, were $189.1 million, net of underwriting discounts and commissions and offering expenses payable by the Company. The Company’s reserved shares of common stock for future issuance are as follows (in thousands): December 31, 2018 December 31, 2017 Reserved for issuance under equity incentive plans 6,999 7,430 Reserved for issuance under employee stock purchase plan 170 206 7,169 7,636

License Revenue

License Revenue	12 Months Ended
	Dec. 31, 2018
License Agreement Revenue Recognition [Abstract]
License Revenue	8. License Revenue Effective January 1, 2018, the Company adopted Topic 606 using the modified retrospective transition method and has applied the new standard to all of its license agreements in effect as of, or entered into after, January 1, 2018. License revenue for periods ending after January 1, 2018 is presented in accordance with the requirements of Topic 606, while prior period amounts have not been adjusted and continue to be reported in accordance with Topic 605 and accordingly, may not be comparable. As of December 31, 2018, the Company’s NAV Technology Platform was being applied in the development of more than 20 partnered product candidates by 11 NAV Technology Licensees. Development milestone payments are only included in the transaction price of each license and recognized as 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 revenue in the period of achievement. As of December 31, 2018, 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 $30.4 million upon the commencement of various stages of clinical trials, $47.5 million upon the submission of regulatory approval filings, $117.5 million upon the approval of commercial products by regulatory agencies and $232.0 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 table presents 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 Year Ended December 31, 2018 Receivables and contract assets: Accounts receivable, current and non-current $ 5,850 $ 25,749 $ 31,599 Contract assets $ 350 $ 400 $ 750 Contract liabilities: Deferred revenue, current and non-current $ — $ 3,933 $ 3,933 The net increase in the balance of accounts receivable during the year ended December 31, 2018 was primarily attributable to the license granted to Abeona in November 2018. As of December 31, 2018, the Company had recorded accounts receivable, current and non-current, of $26.0 million related to the license granted to Abeona in November 2018. As of December 31, 2018, the Company had recorded deferred revenue, current and non-current, of $3.9 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. The net increase in deferred revenue during the year ended December 31, 2018 was attributable to consideration received by the Company for new license options granted during the period. During the year ended December 31, 2018, the Company recognized license revenue of $5.3 million 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 price were primarily attributable to development milestones achieved or deemed probable of achievement during the period that were previously not considered probable of achievement. 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. As of December 31, 2018, the Company had not recognized any impairment losses on its receivables or contract assets from contracts with customers. AveXis, Inc. 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 spinal muscular atrophy (SMA) in humans by in vivo In 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, 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 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. Pursuant to the January 2018 Amendment, in consideration for the additional rights granted thereunder 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 AG (Novartis), which 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 December 31, 2018, the transaction price of the original March 2014 License was $7.5 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 $7.0 million in payments for remaining development milestones that have not yet been achieved and are 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, if any. 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 December 31, 2018, 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, if any. During the year ended December 31, 2018, the Company recognized license revenue of $176.1 million and interest income from licensing of $8.0 million from the March 2014 License, as amended, which includes amounts from both the original March 2014 License and the January 2018 Amendment. 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 are included in current assets and $0.2 million are included in non-current assets on the consolidated balance sheets. During the years ended December 31, 2017 and 2016, the Company recognized license revenue of $1.1 million and $0.1 million, respectively, from the March 2014 License which was recognized under the requirements of Topic 605. As of December 31, 2017, the Company had no amounts receivable from AveXis related to the March 2014 License under the requirements of Topic 605. AveXis, Inc. June 2017 License In June 2017, the Company entered into an exclusive license agreement (the June 2017 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 Rett Syndrome and amyotrophic lateral sclerosis (ALS) caused by mutations in the gene that produces the copper zinc superoxide dismutase 1 (SOD1) in humans by in vivo During the year ended December 31, 2018, the Company recognized license revenue of zero and interest income from licensing of $0.1 million from the June 2017 License. As of December 31, 2018, the Company had recorded $0.8 million of accounts receivable from AveXis under the June 2017 License, of which $0.1 million are included in current assets and $0.7 million are included in non-current assets on the consolidated balance sheets. During the year ended December 31, 2017, the Company recognized license revenue of $6.0 million from the June 2017 License which was recognized under the requirements of Topic 605. As of December 31, 2017, the Company had no amounts receivable from AveXis related to the June 2017 License under the requirements of Topic 605. Abeona Therapeutics Inc. In November 2018, the Company entered into an exclusive license agreement with Abeona. Under the license, the Company granted Abeona an exclusive, worldwide commercial license (subject to certain non-exclusive rights previously granted by the Company), with rights to sublicense, to the NAV AAV9 vector for the treatment of Mucopolysaccharidosis Type IIIA (MPS IIIA), also known as Sanfilippo Syndrome Type A, Mucopolysaccharidosis Type IIIB (MPS IIIB), also known as Sanfilippo Syndrome Type B, Neuronal Ceroid Lipfuscinosis-1 (CLN1 disease), also known as infantile Batten Disease, and Neuronal Ceroid Lipfuscinosis-3 (CLN3 disease), also known as juvenile Batten Disease, by in vivo Accounting Analysis The Company determined that the November 2018 license agreement with Abeona has an initial contract term of three years for revenue recognition purposes due to the lack of a substantive termination penalty for license periods beyond three years from the date of the license agreement. The annual payments due under the agreement beginning in November 2021 represent contract renewal options granted to Abeona for revenue recognition purposes, and therefore are not accounted for under the current license agreement. The Company determined that the contract renewal options do not represent material rights granted to Abeona, and the only material performance obligations of the Company under the current license agreement are for the delivery of the initial intellectual property licenses, which occurred upon the execution of the license agreement in November 2018. Upon its execution, and as of December 31, 2018, the transaction price of the November 2018 license agreement with Abeona was $35.6 million, which was fully recognized as license revenue upon the delivery of the licenses in November 2018. The transaction price includes the following fixed consideration payable to the Company over the initial contract term of three years: (i) the $10.0 million payment in November 2018 and (ii) the present value, as of the date of the license agreement, of the $10.0 million payment due in November 2019 and $20.0 million payment due in November 2020. The discounted portion of the annual payments represents the financing benefit provided to Abeona and is recognized as interest income from licensing over the financing term of two years. Variable consideration under the license agreement, which has been excluded from the transaction price, includes the sales-based milestone payments of $60.0 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, if any. The annual payments due under the agreement beginning in November 2021 represent contract renewal options granted to Abeona for revenue recognition purposes, and therefore are excluded from the transaction price. If renewed by Abeona, each of these payments will be recognized as revenue on the first day of the license renewal period for which the payment relates to, which is the date the payments are due under the agreement. During the year ended December 31, 2018, the Company recognized license revenue of $35.6 million and interest income from licensing of $0.4 million from the license agreement with Abeona. As of December 31, 2018, the Company had recorded $26.0 million of accounts receivable from Abeona under the license agreement, of which $7.5 million are included in current assets and $18.5 million are included in non-current assets on the consolidated balance sheets.

Stock-based Compensation

Stock-based Compensation	12 Months Ended
	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-based Compensation	9. Stock-based Compensation In September 2014, the Board of Directors adopted the 2014 Stock Plan (2014 Plan). In June 2015, the Board of Directors adopted the 2015 Equity Incentive Plan (2015 Plan), which became effective upon the Company’s initial public offering in September 2015. The 2015 Plan replaced the 2014 Plan, and as of the effective date of the 2015 Plan, no further awards may be issued under the 2014 Plan. Any options or awards outstanding under the 2014 Plan as of the effective date of the 2015 Plan remained outstanding and effective. The number of authorized shares under the 2015 Plan automatically increases annually on the first business day of each fiscal year, by the lesser of (i) 4% of the total number of shares of common stock outstanding on December 31 of the prior year, or (ii) a number of common shares determined by the Board of Directors. As of December 31, 2018, the total number of shares of common stock authorized for issuance under the 2015 Plan and 2014 Plan was 9,488,413, of which 2,104,070 remained available for future grants under the 2015 Plan. In January 2019, the Board of Directors authorized an additional 1,444,808 shares to be issued under the 2015 Plan. The 2014 Plan and 2015 Plan provide for the issuance of stock options, stock appreciation rights, restricted and unrestricted stock and unit awards, and performance cash awards to employees, members of the Board of Directors and consultants of the Company. Since the inception of the plans, the Company has issued only stock options and restricted stock units under the plans. Stock options under the 2014 Plan and 2015 Plan generally expire 10 years following the date of grant. Options typically vest over a four-year period, but vesting provisions can vary by award based on the discretion of the Board of Directors. Certain stock option awards granted by the Company include performance conditions that must be achieved in order for vesting to occur. Stock options under the 2014 Plan and 2015 Plan have an exercise price at least equal to the estimated fair value of the Company’s common stock on the date of grant. Restricted stock units vest in accordance with the underlying award agreements and, upon vesting, are settled in common stock of the Company. Shares of common stock underlying awards previously issued under the 2014 Plan and 2015 Plan which are reacquired by the Company, withheld by the Company in payment of the purchase price, exercise price or withholding taxes, expired, cancelled due to forfeiture or otherwise terminated other than by exercise or settlement, are added to the number of shares of common stock available for issuance under the 2015 Plan. Shares available for issuance under the 2015 Plan may be either authorized but unissued shares of the Company’s common stock or common stock reacquired by the Company and held in treasury. The 2015 Plan expires in June 2025, 10 years from the date it was adopted by the Board of Directors, unless earlier terminated. Stock-based Compensation Expense The Company’s stock-based compensation expense by award type is as follows (in thousands): Years Ended December 31, 2018 2017 2016 Stock options $ 15,960 $ 10,031 $ 6,950 Restricted stock units 275 275 23 Employee stock purchase plan 406 299 58 $ 16,641 $ 10,605 $ 7,031 As of December 31, 2018, the Company had $41.6 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 2.7 years. The Company has recorded aggregate stock-based compensation expense in the consolidated statements of operations and comprehensive income (loss) as follows (in thousands): Years Ended December 31, 2018 2017 2016 Research and development $ 7,612 $ 5,128 $ 2,743 General and administrative 9,029 5,477 4,288 $ 16,641 $ 10,605 $ 7,031 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, 2017 5,468 $ 10.25 7.9 $ 125,738 Granted 1,397 $ 41.11 Exercised (1,685 ) $ 8.63 Cancelled or forfeited (325 ) $ 15.95 Outstanding at December 31, 2018 4,855 $ 19.31 7.6 $ 118,185 Exercisable at December 31, 2018 2,535 $ 9.15 6.7 $ 83,529 Vested and expected to vest at December 31, 2018 4,855 $ 19.31 7.6 $ 118,185 (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 years ended December 31, 2018, 2017 and 2016 was $27.49, $13.87 and $8.37, respectively. During the years ended December 31, 2018, 2017 and 2016, the total number of stock options exercised was 1,684,522, 515,916 and 163,158, respectively, resulting in total proceeds of $14.5 million, $2.5 million and $0.2 million, respectively. The total intrinsic value of options exercised during the years ended December 31, 2018, 2017 and 2016 was $68.2 million, $11.1 million and $1.7 million, respectively. The fair values of options granted were estimated at each grant date using the Black-Scholes valuation model with the following weighted-average assumptions: Years Ended December 31, 2018 2017 2016 Expected volatility 75 % 77 % 75 % Expected term (in years) 6.0 6.2 6.2 Risk-free interest rate 2.6 % 2.1 % 1.5 % Expected dividend yield 0.0 % 0.0 % 0.0 % The weighted-average assumptions in the table above for the years ended December 31, 2017 and 2016 exclude options granted to nonemployee advisors, except for members of the Company’s Board of Directors. For the years ended December 31, 2017 and 2016, the Company recognized $0.5 million and $0.6 million, respectively, of stock-based compensation expense related to stock options granted to these nonemployees. Effective July 1, 2018, upon the adoption of ASU 2018-07, Compensation—Stock Compensation (Topic 718): Improvements to Nonemployee Share-based Payment Accounting , options to nonemployees are measured at the estimated grant date value of the awards. Prior to the adoption of ASU 2018-07, stock options granted to nonemployees were remeasured at their fair values at each reporting date until vested. There was no impact to the Company’s financial statements upon the adoption of ASU 2018-07 on July 1, 2018, because as of that date, there were no unvested stock options outstanding which were considered probable of achievement. The weighted-average assumptions in the table above for the year ended December 31, 2018 include all options granted to employees and nonemployees during the period. 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, 2017 40 $ 20.90 Granted — $ — Vested — $ — Forfeited — $ — Unvested balance at December 31, 2018 40 $ 20.90 Employee Stock Purchase Plan In June 2015, the Company’s Board of Directors adopted the 2015 ESPP, which became effective upon the Company’s initial public offering in September 2015. The number of authorized shares reserved for issuance under the 2015 ESPP automatically increases on the first business day of each fiscal year by the lesser of (i) 1% of the shares of common stock outstanding on the last business day of the prior fiscal year; or (ii) the number of shares determined by the Company’s Board of Directors. Unless otherwise determined by the administrator of the 2015 ESPP, two offering periods of six months’ duration will begin each year on January 1 and July 1. As of December 31, 2018, the total number of shares of common stock authorized for issuance under the 2015 ESPP was 254,000, of which 169,580 remained available for future issuance. During the years ended December 31, 2018, 2017 and 2016, 36,700, 47,720 and zero shares of common stock, respectively, were issued under the 2015 ESPP.

Retirement Plan

Retirement Plan	12 Months Ended
	Dec. 31, 2018
Postemployment Benefits [Abstract]
Retirement Plan	10. Retirement Plan The Company sponsors a defined-contribution retirement plan under Section 401(k) of the Internal Revenue Code (the 401(k) Plan). The 401(k) Plan covers all employees who meet defined minimum age and service requirements, and allows participants to defer a portion of their annual compensation. The Company matches employee deferrals up to a specified percentage of eligible compensation. For the years ended December 31, 2018, 2017 and 2016, the Company incurred expenses of $1.3 million, $1.0 million and $0.6 million, respectively, for matching contributions to the 401(k) Plan.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	11. Income Taxes The components of income (loss) before income taxes were as follows (in thousands): Years Ended December 31, 2018 2017 2016 United States $ 104,181 $ (73,138 ) $ (63,402 ) Foreign (65 ) (31 ) — Total income (loss) before income taxes $ 104,116 $ (73,169 ) $ (63,402 ) The components of the provision for income tax expense (benefit) were as follows (in thousands): Years Ended December 31, 2018 2017 2016 Current: Federal $ — $ — $ — State 4,179 — — Foreign — — — Total current 4,179 — — Deferred: Federal — — (381 ) State — — (54 ) Foreign — — — Total deferred — — (435 ) Total income tax expense (benefit) $ 4,179 $ — $ (435 ) The TCJA was signed into law in December 2017 and, among other changes, contains significant changes to corporate taxation, including reduction of the corporate tax rate from a top marginal rate of 35% to a flat rate of 21%, elimination, reduction or limitation of certain domestic deductions and credits, limitation of the deduction for net operating losses (NOLs) to 80% of current year taxable income, elimination of NOL carrybacks, one-time taxation of offshore earnings at reduced rates regardless of whether they are repatriated, elimination of U.S. tax on foreign earnings (subject to certain significant exceptions), immediate deductions for certain new investments instead of deductions for depreciation expense over time, and modification or repeal of many business deductions and credits, including the orphan drug tax credit. Most of the changes resulting from the TCJA were effective beginning in 2018. In December 2017, the SEC staff issued Staff Accounting Bulletin No. 118 (SAB 118), which allowed the Company to record provisional amounts for the effects of the TCJA in the period it was enacted for a measurement period not extend beyond one year from the enactment date. Under SAB 118, the Company recorded a provisional reduction in its deferred tax assets and associated valuation allowance of $17.9 million in 2017 for the effects of the TCJA, which was primarily attributable to the reduction in federal tax rates. The Company completed its assessment of the final impact of the TCJA within the required measurement period under SAB 118 and determined that there were no material adjustments to the provisional amounts previously recorded. A reconciliation of income tax expense (benefit) computed at the statutory federal income tax rate of 21% for the year ended December 31, 2018 and 34% for the years ended December 31, 2017 and 2016, to income tax expense (benefit) as reflected in the financial statements for such periods is as follows (in thousands): Years Ended December 31, 2018 2017 2016 Federal income tax expense (benefit) at statutory rate $ 21,862 $ (24,876 ) $ (21,556 ) State income tax expense (benefit), net of federal tax effect 9,691 (7,756 ) (1,617 ) Research and development credits (7,847 ) (6,297 ) (7,275 ) Stock-based compensation expense for incentive stock options and employee stock purchase plan (6,493 ) (3,012 ) 1,805 Other non-deductible expenses and reconciling items 139 (26 ) 170 Change in corporate tax rates (729 ) 16,598 42 Change in valuation allowance (12,444 ) 25,369 27,996 Total income tax expense (benefit) $ 4,179 $ — $ (435 ) The significant components of the Company’s net deferred tax assets are as follows (in thousands): December 31, 2018 December 31, 2017 Deferred tax assets: Net operating loss carryforwards $ 15,468 $ 37,658 Research and development tax credits 28,984 21,137 Step-up in assets upon conversion to C-corporation 729 721 Stock-based compensation expense for non-qualified stock options and restricted stock units 5,462 4,263 Unrealized losses on marketable securities 101 89 Deferred rent 495 458 Accruals and other 2,772 1,540 Total deferred tax assets before valuation allowance 54,011 65,866 Valuation allowance (51,533 ) (65,669 ) Total deferred tax assets 2,478 197 Deferred tax liabilities: Depreciation (1,207 ) (197 ) Other (1,271 ) — Total deferred tax liabilities (2,478 ) (197 ) Net deferred tax assets $ — $ — The Company has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets. Based on the Company’s history of operating losses, including a three-year cumulative loss position as of 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 December 31, 2018 and 2017. The valuation allowance decreased by $14.1 million during the year ended December 31, 2018, due primarily to the utilization of federal and state NOLs and increases in deferred tax liabilities during the period, the impact of which was offset by research and development credits, stock-based compensation expense and other increases in deferred tax assets during the period. As of December 31, 2018 and 2017, the Company had U.S. federal NOL carryforwards of approximately $56.1 million and $126.7 million, respectively, which may be available to offset future income tax liabilities and expire at various dates though 2037. As of December 31, 2018 and 2017, the Company also had U.S. state NOL carryforwards of approximately $56.2 million and $167.8 million, respectively, which may be available to offset future income tax liabilities and expire at various dates through 2037. As of December 31, 2018 and 2017, the Company had federal research and development and orphan drug tax credit carryforwards of approximately $29.1 million and $21.3 million, respectively, which may be available to reduce future income tax liabilities and expire at various dates through 2038. The calculation of these credits requires assumptions to be made by the Company to estimate qualified research expenses. The Company conducts formal studies to document the qualified activities and expenses used to calculate these credits, however a portion of these credits may be subject to future studies which have not yet occurred, the results of which may result in an adjustment to the Company’s credit carryforwards. The Company accounts for uncertain tax positions in accordance with the requirements of ASC 740, and accordingly, recognizes the tax benefit of tax positions to the extent that the benefit will more likely than not be realized. As of December 31, 2018 and 2017, the Company had unrecognized tax benefits of $0.2 million and $0.1 million, respectively, which were reserved against the credit carryforwards as uncertain tax positions. No reserve for uncertain tax positions has been placed against qualified expenses for which a study has not been conducted. However, a full valuation allowance has been provided against the net credit carryforwards and, if an adjustment is required upon the completion of the study, this adjustment would be offset by an adjustment to the deferred tax asset established for the research and development credit carryforwards and the valuation allowance. Under the provisions of the Internal Revenue Code, the Company’s NOL and tax credit carryforwards are subject to review and possible adjustment by the Internal Revenue Service and state tax authorities. NOL and tax credit carryforwards may be subject to an annual limitation in the event of certain cumulative changes in the ownership interest of significant shareholders over a three-year period in excess of 50%, as defined under Sections 382 and 383 of the Internal Revenue Code, respectively, as well as similar state provisions. This could limit the amount of tax attributes that can be utilized annually to offset future taxable income or tax liabilities. The amount of the annual limitation is determined based on the value of the Company immediately prior to the ownership change. Subsequent ownership changes may further affect the limitation in future years. The Company has completed several financings since its inception which may have resulted in a change in control as defined by Sections 382 and 383 of the Internal Revenue Code, or could result in a change in control in the future. The Company and its subsidiaries file income tax returns in the United States at the federal level and in various states and foreign jurisdictions. The U.S. federal and state income tax returns are generally subject to tax examinations for the tax years ended December 31, 2014 onward. To the extent the Company has tax attribute carryforwards, the tax years in which the attribute was generated may still be adjusted upon examination by the Internal Revenue Service or state tax authorities to the extent utilized in a future period. The Company’s U.S. federal tax return for the year ended December 31, 2015 was examined by the Internal Revenue Service. The Internal Revenue Service completed its examination and made no changes to the amounts reported by the Company.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2018
Related Party Transactions [Abstract]
Related Party Transactions	12. Related Party Transactions FOXKISER LLP For the years ended December 31, 2018, 2017 and 2016, the Company was 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 paid 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 and which has a term of one year and is terminable by either party. Expenses incurred under the agreements with FOXKISER for the years ended December 31, 2018, 2017 and 2016 were $2.1 million, $1.5 million and $1.0 million, respectively, and are recorded as research and development expenses in the consolidated statements of operations and comprehensive income (loss). Scientific Founder In September 2014, the Company entered into an advisory agreement, as amended, with James M. Wilson, M.D., Ph.D., who was formerly the Company’s Chief Scientific Advisor, Chairman of the Company’s Scientific Advisory Board and Special Advisor. The agreement required a fixed monthly payment in consideration for scientific advisory services and expired in March 2017, after which the Company no longer deemed Dr. Wilson to be a related party. During the three months ended March 31, 2017 and the year ended December 31, 2016, the Company incurred advisory fees of $0.1 million and $0.3 million, respectively, under the agreement, which are recorded as research and development expenses in the consolidated statements of operations and comprehensive income (loss). Pursuant to a separate advisory agreement entered into in March 2017, which expired on December 31, 2018, Dr. Wilson provided services at no cost to the Company.

Net Income (Loss) Per Share

Net Income (Loss) Per Share	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Net Income (Loss) Per Share	13. 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): Years Ended December 31, 2018 2017 2016 Basic net income (loss) per share: Net income (loss) applicable to common stockholders $ 99,937 $ (73,169 ) $ (62,967 ) Shares used in computation: Weighted-average common shares outstanding 33,427 29,878 26,409 Basic net income (loss) per share $ 2.99 $ (2.45 ) $ (2.38 ) Diluted net income (loss) per share: Net income (loss) applicable to common stockholders $ 99,937 $ (73,169 ) $ (62,967 ) Shares used in computation: Weighted-average common shares outstanding 33,427 29,878 26,409 Stock options 3,186 — — Restricted stock units 32 — — Employee stock purchase plan 3 — — Weighted-average diluted common shares 36,648 29,878 26,409 Diluted net income (loss) per share $ 2.73 $ (2.45 ) $ (2.38 ) 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): Years Ended December 31, 2018 2017 2016 Stock options issued and outstanding 928 5,468 5,118 Unvested restricted stock units outstanding — 40 40 Employee stock purchase plan — 20 22 928 5,528 5,180

Supplemental Disclosures

Supplemental Disclosures	12 Months Ended
	Dec. 31, 2018
Payables And Accruals [Abstract]
Supplemental Disclosures	14. Supplemental Disclosures Accrued expenses and other current liabilities consists of the following (in thousands): December 31, 2018 December 31, 2017 Accrued personnel costs $ 9,484 $ 5,789 Accrued external research and development expenses 4,274 2,072 Accrued licensing costs 1,617 — Accrued external general and administrative expenses 773 1,078 Accrued income taxes payable 726 — Accrued purchases of property and equipment 221 430 Other accrued expenses and current liabilities 69 236 $ 17,164 $ 9,605 Other liabilities of $2.5 million reported as of December 31, 2018 consists of accrued licensing costs payable in periods beyond 12 months from the reporting date.

Selected Quarterly Financial In

Selected Quarterly Financial Information (Unaudited)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Information (Unaudited)	15. Selected Quarterly Financial Information (Unaudited) The following table contains quarterly financial information for the years ended December 31, 2018 and 2017. Management believes that the following information reflects all normal recurring adjustments necessary for a fair statement of the information for the periods presented. The operating results for any quarter are not necessarily indicative of results for any future period. Amounts in the following table are in thousands, except per share data. Quarters Ended March 31, 2018 June 30, 2018 September 30, 2018 December 31, 2018 Total revenues $ 132,391 $ 40,031 $ 5,306 $ 40,777 Total costs of revenues $ 2,408 $ 3,872 $ 517 $ 2,843 Research and development expense $ 19,550 $ 21,486 $ 18,508 $ 24,329 General and administrative expense $ 8,380 $ 8,318 $ 9,008 $ 11,144 Total operating expenses $ 30,366 $ 33,681 $ 28,031 $ 38,327 Net income (loss) $ 104,239 $ 10,594 $ (19,202 ) $ 4,306 Basic net income (loss) per share $ 3.30 $ 0.33 $ (0.56 ) $ 0.12 Diluted net income (loss) per share $ 3.04 $ 0.30 $ (0.56 ) $ 0.11 Quarters Ended March 31, 2017 June 30, 2017 September 30, 2017 December 31, 2017 Total revenues $ 455 $ 6,562 $ 1,336 $ 2,040 Total costs of revenues $ 91 $ 1,317 $ 683 $ (382 ) Research and development expense $ 16,619 $ 13,917 $ 12,518 $ 14,170 General and administrative expense $ 6,622 $ 6,355 $ 9,444 $ 4,808 Total operating expenses $ 23,377 $ 21,618 $ 22,645 $ 18,638 Net income (loss) $ (21,993 ) $ (14,473 ) $ (20,706 ) $ (15,997 ) Basic net income (loss) per share $ (0.82 ) $ (0.47 ) $ (0.67 ) $ (0.51 ) Diluted net income (loss) per share $ (0.82 ) $ (0.47 ) $ (0.67 ) $ (0.51 )

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation and Principles of Consolidation	Basis of Presentation and Principles of Consolidation The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (GAAP). 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.
Foreign Currency Transactions	Foreign Currency Transactions The functional currency of the Company and its consolidated subsidiaries is the U.S. dollar. Transaction gains and losses that arise from exchange rate fluctuations on transactions denominated in a currency other than the U.S. dollar are included in results of operations as incurred.
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: 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.
Segment and Geographical Information	Segment and Geographical Information Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision maker (CODM), or decision-making group, in making decisions on how to allocate resources and assess performance. The Company’s CODM, the Chief Executive Officer, views its operations and manages its business as one operating segment. The Company’s revenue primarily consists of license revenue. For the year ended December 31, 2018, 99% of the Company’s revenue was generated from customers located in the U.S. For the year ended December 31, 2017, 96% of the Company’s revenue was generated from customers located in the U.S. For the year ended December 31, 2016, 90% of the Company’s revenue was generated from customers located in the U.S. Country of origin for license revenue is determined based on the country of domicile of the licensee. The substantial majority of the Company’s assets currently reside in the U.S.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments purchased with original maturities of 90 days or less at acquisition to be cash equivalents.
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): December 31, 2018 December 31, 2017 December 31, 2016 Cash and cash equivalents $ 75,561 $ 46,656 $ 24,840 Restricted cash 1,053 225 225 Total cash and cash equivalents and restricted cash $ 76,614 $ 46,881 $ 25,065
Marketable Securities	Marketable Securities Marketable securities consist of debt securities and are classified as available-for-sale and carried at fair value. Marketable 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. Unrealized gains and losses, 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. Purchase premiums and discounts 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. 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. A decline in the fair value below cost of available-for-sale 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 investments below their cost are other-than-temporary. The evaluation includes consideration of the cause of the impairment, including the creditworthiness of the security issuers, the number of securities in an unrealized loss position, the severity and duration of the unrealized losses, whether the Company has the intent to sell the securities and whether it is more likely than not that the Company will be required to sell the securities before the recovery of their amortized cost basis. The Company has not recorded any impairment of available-for-sale securities which was deemed to be to be other-than-temporary.
Concentrations of Credit Risk and Off-balance Sheet Risk	Concentrations of Credit Risk and Off-balance Sheet Risk Cash and cash equivalents, marketable securities and accounts receivable are financial instruments that are potentially subject to concentrations of credit risk. The Company’s cash and cash equivalents are deposited in accounts at multiple financial institutions, and amounts may exceed federally insured limits. The Company believes it is not exposed to significant credit risk due to the financial strength of the depository institutions in which the cash and cash equivalents are held. The Company’s marketable securities consist of investment grade debt securities and may be subject to concentrations of credit risk. The Company has adopted an investment policy which limits potential concentrations of investments and establishes minimum acceptable credit ratings, thereby reducing credit risk exposure. 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. The Company has no financial instruments with off-balance sheet risk of loss. The following table summarizes those customers who represented at least 10% of revenue or accounts receivable, current and non-current, for the periods presented: Revenue Accounts Receivable Years Ended December 31, December 31, 2018 2017 2016 2018 2017 Customer A 81 % 68 % * * * Customer B 16 % * * 82 % * Customer C * * 24 % * * Customer D * * * * 42 % Customer E * * * * 32 % Customer F * * 44 % * * Customer G * * * * 21 % * Represented less than 10%
Accounts Receivable	Accounts Receivable Accounts receivable primarily consist of consideration due to the Company resulting from its license agreements with NAV Technology Licensees. Accounts receivable include amounts invoiced to licensees as well as rights to consideration which have not yet been invoiced and for which payment is conditional solely upon the passage of time. If a licensee elects to terminate a license prior to the end of the license term, the licensed intellectual property is returned to the Company and any accounts receivable from the licensee which are not contractually payable to the Company are charged off as a reduction of license revenue in the period of the termination. Accounts receivable which are not expected to be received by the Company within 12 months from the reporting date are stated net of a discount to present value and recorded as non-current assets on the consolidated balance sheets. The present value discount is recognized as a reduction of revenue in the period in which the accounts receivable are initially recorded and is accreted as interest income from licensing over the term of the receivables. Accounts receivable are stated net of an allowance for doubtful accounts, if deemed necessary based on the Company’s evaluation of collectability using specific identification of account balances, the credit profile and financial condition of its customers and historical information regarding write-offs. Account balances are charged off against the allowance when the potential for recovery is considered remote. The Company did not record an allowance for doubtful accounts as of December 31, 2018 or 2017.
Property and Equipment	Property and Equipment Property and equipment is stated at cost less accumulated depreciation and amortization. Maintenance and repairs that do not improve or extend the lives of the respective assets are expensed to operations as incurred. Upon disposal, the related cost and accumulated depreciation is removed from the accounts and any resulting gain or loss is included in the results of operations. Depreciation and amortization is calculated using the straight-line method over the estimated useful lives of the assets, which are as follows: Computer equipment and software 3 years Lab equipment 5 years Furniture and fixtures 5 years Leasehold improvements Shorter of lease term or estimated useful life Certain estimated construction costs incurred and reported by the Company’s landlord at 9800 Medical Center Drive are recorded as property and equipment, with a corresponding financing lease obligation, on the consolidated balance sheets. Please refer to Note 6 for further information on the Company’s lease agreements.
Impairment of Long-lived Assets	Impairment of Long-lived Assets The Company reviews long-lived assets when events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Recoverability is measured by comparison of the book values of the assets to estimated future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the book value of the assets exceed their fair value, which is measured based on the projected discounted future net cash flows arising from the assets. No impairment losses have been recorded during the years ended December 31, 2018, 2017 and 2016.
Non-marketable Equity Securities	Non-marketable Equity Securities The Company’s non-marketable equity securities do not have readily determinable fair values and consist of equity investments in other entities in which the Company’s ownership interest is below 20% and the Company does not have significant influence over the operations of the entity. Prior to January 1, 2018, non-marketable equity securities were accounted for using the cost method and measured at cost less impairment. Beginning January 1, 2018, upon the Company’s adoption of Accounting Standards Update (ASU) 2016-01, Financial Instruments—Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities Declines in the fair value of non-marketable equity securities below their carrying values that are deemed to be other-than-temporary are charged to results of operations as realized losses. In estimating other-than-temporary impairment losses, management considers, among other things, the length of time and the extent to which the fair value has been less than cost, the financial condition and near-term prospects of the issuer and the intent and ability of the Company to retain its investments in the issuer for a period of time sufficient to allow for the anticipated recovery in fair value. The Company has not recorded any other-than-temporary impairment losses on its non-marketable equity securities.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company is required to disclose information on all assets and liabilities reported at fair value that enables an assessment of the inputs used in determining the reported fair values. Accounting Standards Codification (ASC) Topic 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 Effective January 1, 2018, the Company adopted ASU 2014-09, Revenue from Contracts with Customers Revenue Recognition Topic 606 requires entities to recognize revenue when control of the promised goods or services is transferred to customers at an amount that reflects the consideration to which the entity expects to be entitled to in exchange for those goods or services. The following five steps are performed to determine the appropriate revenue recognition for arrangements within the scope of Topic 606: (i) identify the contract(s) with a customer, (ii) identify the performance obligations in the contract, (iii) determine the transaction price, (iv) allocate the transaction price to the performance obligations in the contract and (v) recognize revenue when (or as) the entity satisfies the performance obligations. 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 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 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. 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 in the consolidated statements of operations 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. To date the Company has not recognized any revenue from royalties on sales of licensed products or the achievement of sales-based milestones. 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 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. Other Revenues Other revenues consist of sales of licensed reagents to third parties for use in research and development and grant revenue generated through research and development grant programs offered by the European Union. Revenue from reagent sales is recognized when control of the licensed reagents is transferred to the customer. Grant revenue is recognized in the period in which the related costs are incurred and the related services are rendered by the Company. As of December 31, 2017, all grant programs were completed.
Cost of Revenues	Costs of Revenues Licensing costs consist of sublicense fees to licensors as a result of license revenues generated by the Company. Sublicense fees are based on a percentage of license fees received by the Company from licensees as specified in the Company’s agreements with its licensors. The Company recognizes sublicense fees in the period that the underlying license revenue is recognized. Sublicense fees payable by the Company to licensors in periods beyond 12 months from the reporting date are recorded as non-current liabilities on the consolidated balance sheets. Other costs of revenue consist of royalties to licensors as a result of the sales of licensed reagents by the Company. The Company recognizes royalties on sales of licensed reagents in the period that the underlying sales occur.
Research and Development Expense	Research and Development Expenses Research and development costs are expensed as incurred. Advance payments for goods or services related to research and development activities are deferred and expensed as the goods are delivered or the related services are performed. Research and development costs include salaries, benefits and other personnel costs, laboratory and facilities costs and other overhead costs allocated to research and development activities. Additionally, research and development costs include goods and services associated with preclinical research, clinical trial activities, manufacturing-related activities, regulatory and other related services performed by third-parties. At the end of each reporting period, the Company compares payments made to third-party service providers to the estimated expenses incurred based on the services provided and progress toward completion of the research or development objectives. Such estimates are subject to change as additional information becomes available. Depending on the timing of payments to the service providers and the estimated expenses incurred, the Company may record net prepaid or accrued research and development expenses relating to these costs. Up-front fees incurred in obtaining technology licenses, as well as milestone payments to licensors, are charged to research and development expense as incurred if the technology licensed has no alternative future use.
Stock-based Compensation	Stock-based Compensation The Company accounts for its stock-based compensation awards in accordance with ASC 718, Compensation—Stock Compensation The Company’s stock-based awards are subject to either service or performance-based vesting conditions. Compensation expense related to awards to employees and nonemployees with service-based vesting conditions is recognized on a straight-line basis based on the estimated grant date fair value over the requisite service period of the award, which is generally the vesting term. Compensation expense related to awards to employees and nonemployees with performance-based vesting conditions is recognized based on the estimated grant date fair value over the requisite service period using the accelerated attribution method to the extent achievement of the performance condition is probable. The Company estimates the fair value of its stock option awards using the Black-Scholes option-pricing model, which requires the input of subjective assumptions, including (i) the fair value of the underlying common stock, (ii) the expected stock price volatility, (iii) the expected term of the award, (iv) the risk-free interest rate and (v) expected dividends. The Company does not have sufficient historical and implied volatility data for its common stock necessary to estimate the expected the volatility of its common stock over a period of time commensurate with the expected term of its stock option awards. As a result, the Company estimates expected volatility based on the historical volatility of both its common stock and the common stock of a selected peer group of similar publicly traded companies for which sufficient historical volatility data is available. Due to the lack of historical volatility data for its common stock, the Company places a higher weight on the historical volatility of the selected peer group in estimating expected volatility. The Company computes the historical volatility data using the daily closing prices for the selected companies’ shares during a period equivalent to the expected term of the stock option awards. For the purpose of identifying the selected peer group companies, the Company considers characteristics such as enterprise value, risk profiles, position within the industry and length of historical share price information. The Company plans to continue using historical peer group volatility data as an input to estimate expected volatility until a sufficient amount of historical volatility data for its common stock becomes available. The Company estimates the expected term of its employee stock options using the “simplified” method, whereby, the expected term equals the arithmetic average of the vesting term and the original contractual term of the option due to its lack of sufficient historical data. For stock options granted to nonemployees, the Company uses the contractual term of the award rather than expected term to estimate the fair value of the award. The Company estimates the risk-free interest rates for periods within the expected term of its options based on the rates of U.S. Treasury securities with maturity dates commensurate with the expected term of the associated awards. The Company has never paid and does not expect to pay dividends in the foreseeable future. The Company estimates the fair value of restricted stock units based on the fair value of the Company’s common stock on the date of the grant. On July 1, 2018, the Company adopted ASU 2018-07, Compensation—Stock Compensation (Topic 718): Improvements to Nonemployee Share-based Payment Accounting For the year ended December 31, 2016, the Company was also required to estimate forfeitures of stock-based awards at the time of grant and revise those estimates in subsequent periods if actual forfeitures differ from its estimates. For all periods through December 31, 2016, a forfeiture rate of zero was used to calculate stock-based compensation expense due to the lack of historical information necessary to estimate forfeitures. To the extent that actual forfeitures differed from the Company’s estimates, the differences were recorded as a cumulative adjustment in the period the estimates were revised. On January 1, 2017, the Company adopted ASU 2016‑09, Compensation—Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting
Income Taxes	Income Taxes Income taxes are recorded in accordance with ASC 740, Income Taxes The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit will more likely than not be realized. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances. The Company will recognize interest and penalties related to uncertain tax positions in income tax expense. As of December 31, 2018 and 2017, the Company had no accrued interest or penalties related to uncertain tax positions and no amounts have been recognized in the Company’s consolidated statements of operations and comprehensive income (loss).
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.
Comprehensive Income (Loss)	Comprehensive Income (Loss) The Company’s comprehensive income (loss) includes its net income (loss) as well as net unrealized gains and losses on available-for-sale securities, net of income tax effects and reclassification adjustments for realized gains and losses.
Recent Accounting Pronouncements	Recent Accounting Pronouncements Adoption of ASU 2014-09, Revenue from Contracts with Customers In May 2014, the Financial Accounting Standards Board (FASB) issued ASU 2014-09, Revenue from Contracts with Customers Revenue Recognition The Company recorded a net reduction in opening accumulated deficit of $4.8 million as of January 1, 2018 for the cumulative impact of adoption of Topic 606, which was primarily the result of accelerated recognition of license revenue related to annual license fees under Topic 606. Under Topic 605, annual license fees payable to the Company by licensees were recognized as license revenue annually when the amounts became fixed or determinable. Under Topic 606, the present value of aggregate annual license fees over the contract term of the license agreement are recognized as revenue upon the delivery of the license to the licensee. The impact of the accelerated recognition of license revenue upon adoption was partially offset by the accelerated recognition of licensing costs to the Company’s licensors. The Company recognizes sublicense fees to its licensors in the period the underlying license revenue is recognized. The cumulative adjustment for the adoption of Topic 606 had the following effects on the Company’s consolidated balance sheet as of January 1, 2018 (in thousands): Cumulative Adjustment for Balance at Adoption of Balance at December 31, 2017 Topic 606 January 1, 2018 Consolidated Balance Sheet Assets: Accounts receivable, current $ 473 $ 527 $ 1,000 Accounts receivable, non-current $ — $ 4,850 $ 4,850 Other current assets $ 1,412 $ 350 $ 1,762 Liabilities: Accrued expenses and other current liabilities $ 9,605 $ 105 $ 9,710 Other liabilities $ — $ 819 $ 819 Stockholdersʼ Equity: Accumulated deficit $ (187,756 ) $ 4,803 $ (182,953 ) The following tables present the effects of the adoption of Topic 606 on each financial statement line item of the Company’s consolidated financial statements as of and for the year ended December 31, 2018 (in thousands, except per share data): As of December 31, 2018 Impact of Results Without Adoption of Adoption of As Reported Topic 606 Topic 606 Consolidated Balance Sheet Assets: Accounts receivable, current $ 8,587 $ (1,803 ) $ 10,390 Accounts receivable, non-current $ 23,012 $ 3,012 $ 20,000 Prepaid expenses $ 5,734 $ 60 $ 5,674 Other current assets $ 3,831 $ 750 $ 3,081 Other assets $ 2,315 $ 267 $ 2,048 Liabilities: Accrued expenses and other current liabilities $ 17,164 $ (580 ) $ 17,744 Deferred revenue, current $ 600 $ 600 $ — Deferred revenue, non-current $ 3,333 $ 3,333 $ — Other liabilities $ 2,505 $ 705 $ 1,800 Stockholdersʼ Equity: Accumulated deficit $ (83,016 ) $ (1,772 ) $ (81,244 ) Year Ended December 31, 2018 Impact of Results Without Adoption of Adoption of As Reported Topic 606 Topic 606 Consolidated Statement of Operations Revenues: License revenue $ 218,505 $ (16,647 ) $ 235,152 Operating Expenses: Licensing costs $ 9,640 $ (396 ) $ 10,036 Other Income: Interest income from licensing $ 8,946 $ 8,946 $ — Income Tax Expense $ (4,179 ) $ 730 $ (4,909 ) Net Income $ 99,937 $ (6,575 ) $ 106,512 Net Income Per Share: Basic $ 2.99 $ (0.20 ) $ 3.19 Diluted $ 2.73 $ (0.18 ) $ 2.91 Year Ended December 31, 2018 Impact of Results Without Adoption of Adoption of As Reported Topic 606 Topic 606 Consolidated Statement of Cash Flows Cash Flows from Operating Activities: Net income $ 99,937 $ (6,575 ) $ 106,512 Imputed interest income from licensing $ (8,946 ) $ (8,946 ) $ — Changes in accounts receivable $ (16,803 ) $ 13,114 $ (29,917 ) Changes in prepaid expenses $ (400 ) $ (60 ) $ (340 ) Changes in other current assets $ (2,069 ) $ (400 ) $ (1,669 ) Changes in other assets $ (1,453 ) $ (267 ) $ (1,186 ) Changes in accrued expenses and other current liabilities $ 7,582 $ (685 ) $ 8,267 Changes in deferred revenue $ 3,933 $ 3,933 $ — Changes in other liabilities $ 1,686 $ (114 ) $ 1,800 The most significant effects that the adoption of Topic 606 had on the results of operations for the year ended December 31, 2018, as compared to what results would have been if Topic 605 had continued to be applied, were (i) the amount of revenue and interest income from licensing recognized as a result of significant financing components identified within the Company’s license agreements, and (ii) the amount of revenue recognized from license options granted during the period. Under Topic 606, if a significant financing component is identified within a license agreement, the Company is required to adjust the amount of revenue recognized upon the delivery of the license to the present value of the underlying consideration. The discounted portion of the consideration is recognized as interest income from licensing over the financing term of the license agreement. Under Topic 605, the amount of revenue recognized from the delivery of licenses is not adjusted for significant financing components. During the year ended December 31, 2018, the Company recognized $8.9 million of interest income from licensing as a result of significant financing components identified in its license agreements. Under Topic 605, the Company would not have recognized any interest income from significant financing components during the period, and would have recognized $12.4 million of additional license revenue during the period related to its March 2014 license agreement, as amended, with AveXis, Inc. (AveXis) and its November 2018 license agreement with Abeona Therapeutics Inc. (Abeona). Additionally, under Topic 606, the Company recorded deferred revenue of $3.9 million as of December 31, 2018 for consideration received during the period related to license options granted to licensees which were deemed material rights to the licensee to acquire additional licenses in the future. Under Topic 605, the Company would have recognized the $3.9 million of consideration received as license revenue during the period as the options would have been considered substantive and excluded from the contract for accounting purposes until exercised. Other recently adopted accounting pronouncements In June 2018, the FASB issued ASU 2018-07, Compensation—Stock Compensation (Topic 718): Improvements to Nonemployee Share-based Payment Accounting Equity—Equity-based Payments to Nonemployees. In May 2017, the FASB issued ASU 2017-09, Compensation—Stock Compensation (Topic 718): Scope of Modification Accounting In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash In January 2016, the FASB issued ASU 2016-01, Financial Instruments—Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities, Technical Corrections and Improvements to Financial Instruments—Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities Recent accounting pronouncements not yet adopted In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement In 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) In June 2016, the FASB issued ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) Leases (Topic 840) leases with a term of 12 months or less will be accounted for similar to existing guidance for operating leases. eases with a term of 12 months or less as operating leases similar to existing guidance.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2018
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): December 31, 2018 December 31, 2017 December 31, 2016 Cash and cash equivalents $ 75,561 $ 46,656 $ 24,840 Restricted cash 1,053 225 225 Total cash and cash equivalents and restricted cash $ 76,614 $ 46,881 $ 25,065
Schedule of Revenue or Accounts Receivable by Major Customers	The following table summarizes those customers who represented at least 10% of revenue or accounts receivable, current and non-current, for the periods presented: Revenue Accounts Receivable Years Ended December 31, December 31, 2018 2017 2016 2018 2017 Customer A 81 % 68 % * * * Customer B 16 % * * 82 % * Customer C * * 24 % * * Customer D * * * * 42 % Customer E * * * * 32 % Customer F * * 44 % * * Customer G * * * * 21 % * Represented less than 10%
Summary of Estimated Useful Lives of Assets	Depreciation and amortization is calculated using the straight-line method over the estimated useful lives of the assets, which are as follows: Computer equipment and software 3 years Lab equipment 5 years Furniture and fixtures 5 years Leasehold improvements Shorter of lease term or estimated useful life
ASU 2014-09 [Member]
Schedule of Impact on Financial Statements on Adoption of Topic 606	The cumulative adjustment for the adoption of Topic 606 had the following effects on the Company’s consolidated balance sheet as of January 1, 2018 (in thousands): Cumulative Adjustment for Balance at Adoption of Balance at December 31, 2017 Topic 606 January 1, 2018 Consolidated Balance Sheet Assets: Accounts receivable, current $ 473 $ 527 $ 1,000 Accounts receivable, non-current $ — $ 4,850 $ 4,850 Other current assets $ 1,412 $ 350 $ 1,762 Liabilities: Accrued expenses and other current liabilities $ 9,605 $ 105 $ 9,710 Other liabilities $ — $ 819 $ 819 Stockholdersʼ Equity: Accumulated deficit $ (187,756 ) $ 4,803 $ (182,953 ) The following tables present the effects of the adoption of Topic 606 on each financial statement line item of the Company’s consolidated financial statements as of and for the year ended December 31, 2018 (in thousands, except per share data): As of December 31, 2018 Impact of Results Without Adoption of Adoption of As Reported Topic 606 Topic 606 Consolidated Balance Sheet Assets: Accounts receivable, current $ 8,587 $ (1,803 ) $ 10,390 Accounts receivable, non-current $ 23,012 $ 3,012 $ 20,000 Prepaid expenses $ 5,734 $ 60 $ 5,674 Other current assets $ 3,831 $ 750 $ 3,081 Other assets $ 2,315 $ 267 $ 2,048 Liabilities: Accrued expenses and other current liabilities $ 17,164 $ (580 ) $ 17,744 Deferred revenue, current $ 600 $ 600 $ — Deferred revenue, non-current $ 3,333 $ 3,333 $ — Other liabilities $ 2,505 $ 705 $ 1,800 Stockholdersʼ Equity: Accumulated deficit $ (83,016 ) $ (1,772 ) $ (81,244 ) Year Ended December 31, 2018 Impact of Results Without Adoption of Adoption of As Reported Topic 606 Topic 606 Consolidated Statement of Operations Revenues: License revenue $ 218,505 $ (16,647 ) $ 235,152 Operating Expenses: Licensing costs $ 9,640 $ (396 ) $ 10,036 Other Income: Interest income from licensing $ 8,946 $ 8,946 $ — Income Tax Expense $ (4,179 ) $ 730 $ (4,909 ) Net Income $ 99,937 $ (6,575 ) $ 106,512 Net Income Per Share: Basic $ 2.99 $ (0.20 ) $ 3.19 Diluted $ 2.73 $ (0.18 ) $ 2.91 Year Ended December 31, 2018 Impact of Results Without Adoption of Adoption of As Reported Topic 606 Topic 606 Consolidated Statement of Cash Flows Cash Flows from Operating Activities: Net income $ 99,937 $ (6,575 ) $ 106,512 Imputed interest income from licensing $ (8,946 ) $ (8,946 ) $ — Changes in accounts receivable $ (16,803 ) $ 13,114 $ (29,917 ) Changes in prepaid expenses $ (400 ) $ (60 ) $ (340 ) Changes in other current assets $ (2,069 ) $ (400 ) $ (1,669 ) Changes in other assets $ (1,453 ) $ (267 ) $ (1,186 ) Changes in accrued expenses and other current liabilities $ 7,582 $ (685 ) $ 8,267 Changes in deferred revenue $ 3,933 $ 3,933 $ — Changes in other liabilities $ 1,686 $ (114 ) $ 1,800

Marketable Securities (Tables)

Marketable Securities (Tables)	12 Months Ended
	Dec. 31, 2018
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 solely of available-for-sale debt securities (in thousands): 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 Amortized Cost Unrealized Gains Unrealized Losses Fair Value December 31, 2017 Corporate bonds $ 130,018 $ 2 $ (282 ) $ 129,738 $ 130,018 $ 2 $ (282 ) $ 129,738
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 marketable 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 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 ) Less than 12 Months 12 Months or Greater Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses December 31, 2017 Corporate bonds $ 109,238 $ (180 ) $ 17,124 $ (102 ) $ 126,362 $ (282 ) $ 109,238 $ (180 ) $ 17,124 $ (102 ) $ 126,362 $ (282 )

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2018
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 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 Quoted Significant prices other Significant in active observable unobservable markets inputs inputs (Level 1) (Level 2) (Level 3) Total December 31, 2017 Cash equivalents: Money market mutual funds $ — $ 46,646 $ — $ 46,646 Total cash equivalents — 46,646 — 46,646 Marketable securities: Corporate bonds — 129,738 — 129,738 Total marketable securities — 129,738 — 129,738 Total cash equivalents and marketable securities $ — $ 176,384 $ — $ 176,384

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	12 Months Ended
	Dec. 31, 2018
Property Plant And Equipment [Abstract]
Schedule of Property and Equipment	Property and equipment, net consists of the following (in thousands): December 31, 2018 December 31, 2017 Lab equipment $ 14,417 $ 8,561 Computer equipment and software 2,002 1,481 Furniture and fixtures 1,915 1,384 Leasehold improvements 11,751 5,828 Construction-in-progress 5,854 — Total property and equipment 35,939 17,254 Accumulated depreciation and amortization (7,237 ) (3,277 ) Property and equipment, net $ 28,702 $ 13,977

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2018
Schedule of Future Minimum Lease Payments Under 9800 Medical Center Drive Lease and Other Operating Leases	As of December 31, 2018, future minimum lease payments under 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 sheets. The actual timing and amounts of payments under the lease are subject to adjustment based on the completion date of construction and actual square footage of the facility.
The Trustees of the University of Pennsylvania [Member]
Summary of Expenses Incurred by Company	Expenses incurred by the Company related to its license from Penn were recorded as follows (in thousands): Years Ended December 31, 2018 2017 2016 Licensing costs $ (18 ) $ 207 $ 430 Other costs of revenue — 4 11 General and administrative 130 233 133 $ 112 $ 444 $ 574
GlaxoSmithKline LLC [Member]
Summary of Expenses Incurred by Company	Expenses incurred by the Company related to its license from GSK were recorded as follows (in thousands): Years Ended December 31, 2018 2017 2016 Licensing costs $ 9,407 $ 1,497 $ 430 Other costs of revenue — 2 7 General and administrative 548 509 597 $ 9,955 $ 2,008 $ 1,034

Capitalization (Tables)

Capitalization (Tables)	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Schedule of Reserved Shares of Common Stock for Future Issuance	The Company’s reserved shares of common stock for future issuance are as follows (in thousands): December 31, 2018 December 31, 2017 Reserved for issuance under equity incentive plans 6,999 7,430 Reserved for issuance under employee stock purchase plan 170 206 7,169 7,636

License Revenue (Tables)

License Revenue (Tables)	12 Months Ended
	Dec. 31, 2018
License Agreement Revenue Recognition [Abstract]
Summary of Changes in Balances of Receivables, Contract Assets and Contract Liabilities	The following table presents 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 Year Ended December 31, 2018 Receivables and contract assets: Accounts receivable, current and non-current $ 5,850 $ 25,749 $ 31,599 Contract assets $ 350 $ 400 $ 750 Contract liabilities: Deferred revenue, current and non-current $ — $ 3,933 $ 3,933

Stock-based Compensation (Table

Stock-based Compensation (Tables)	12 Months Ended
	Dec. 31, 2018
Stock-Based Compensation Expense by Award Type	The Company’s stock-based compensation expense by award type is as follows (in thousands): Years Ended December 31, 2018 2017 2016 Stock options $ 15,960 $ 10,031 $ 6,950 Restricted stock units 275 275 23 Employee stock purchase plan 406 299 58 $ 16,641 $ 10,605 $ 7,031
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): Years Ended December 31, 2018 2017 2016 Research and development $ 7,612 $ 5,128 $ 2,743 General and administrative 9,029 5,477 4,288 $ 16,641 $ 10,605 $ 7,031
Schedule of Fair Value of Options Granted on Weighted-Average Assumptions	The fair values of options granted were estimated at each grant date using the Black-Scholes valuation model with the following weighted-average assumptions: Years Ended December 31, 2018 2017 2016 Expected volatility 75 % 77 % 75 % Expected term (in years) 6.0 6.2 6.2 Risk-free interest rate 2.6 % 2.1 % 1.5 % Expected dividend yield 0.0 % 0.0 % 0.0 %
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, 2017 40 $ 20.90 Granted — $ — Vested — $ — Forfeited — $ — Unvested balance at December 31, 2018 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, 2017 5,468 $ 10.25 7.9 $ 125,738 Granted 1,397 $ 41.11 Exercised (1,685 ) $ 8.63 Cancelled or forfeited (325 ) $ 15.95 Outstanding at December 31, 2018 4,855 $ 19.31 7.6 $ 118,185 Exercisable at December 31, 2018 2,535 $ 9.15 6.7 $ 83,529 Vested and expected to vest at December 31, 2018 4,855 $ 19.31 7.6 $ 118,185 (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.

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Components of Income (Loss) Before Income Taxes	The components of income (loss) before income taxes were as follows (in thousands): Years Ended December 31, 2018 2017 2016 United States $ 104,181 $ (73,138 ) $ (63,402 ) Foreign (65 ) (31 ) — Total income (loss) before income taxes $ 104,116 $ (73,169 ) $ (63,402 )
Components of the Provision For Income Tax Expense (Benefit)	The components of the provision for income tax expense (benefit) were as follows (in thousands): Years Ended December 31, 2018 2017 2016 Current: Federal $ — $ — $ — State 4,179 — — Foreign — — — Total current 4,179 — — Deferred: Federal — — (381 ) State — — (54 ) Foreign — — — Total deferred — — (435 ) Total income tax expense (benefit) $ 4,179 $ — $ (435 )
Schedule of Reconciliation of Effective Income Tax Expense (Benefit)	A reconciliation of income tax expense (benefit) computed at the statutory federal income tax rate of 21% for the year ended December 31, 2018 and 34% for the years ended December 31, 2017 and 2016, to income tax expense (benefit) as reflected in the financial statements for such periods is as follows (in thousands): Years Ended December 31, 2018 2017 2016 Federal income tax expense (benefit) at statutory rate $ 21,862 $ (24,876 ) $ (21,556 ) State income tax expense (benefit), net of federal tax effect 9,691 (7,756 ) (1,617 ) Research and development credits (7,847 ) (6,297 ) (7,275 ) Stock-based compensation expense for incentive stock options and employee stock purchase plan (6,493 ) (3,012 ) 1,805 Other non-deductible expenses and reconciling items 139 (26 ) 170 Change in corporate tax rates (729 ) 16,598 42 Change in valuation allowance (12,444 ) 25,369 27,996 Total income tax expense (benefit) $ 4,179 $ — $ (435 )
Components of Net Deferred Tax Assets	The significant components of the Company’s net deferred tax assets are as follows (in thousands): December 31, 2018 December 31, 2017 Deferred tax assets: Net operating loss carryforwards $ 15,468 $ 37,658 Research and development tax credits 28,984 21,137 Step-up in assets upon conversion to C-corporation 729 721 Stock-based compensation expense for non-qualified stock options and restricted stock units 5,462 4,263 Unrealized losses on marketable securities 101 89 Deferred rent 495 458 Accruals and other 2,772 1,540 Total deferred tax assets before valuation allowance 54,011 65,866 Valuation allowance (51,533 ) (65,669 ) Total deferred tax assets 2,478 197 Deferred tax liabilities: Depreciation (1,207 ) (197 ) Other (1,271 ) — Total deferred tax liabilities (2,478 ) (197 ) Net deferred tax assets $ — $ —

Net Income (Loss) Per Share (Ta

Net Income (Loss) Per Share (Tables)	12 Months Ended
	Dec. 31, 2018
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): Years Ended December 31, 2018 2017 2016 Basic net income (loss) per share: Net income (loss) applicable to common stockholders $ 99,937 $ (73,169 ) $ (62,967 ) Shares used in computation: Weighted-average common shares outstanding 33,427 29,878 26,409 Basic net income (loss) per share $ 2.99 $ (2.45 ) $ (2.38 ) Diluted net income (loss) per share: Net income (loss) applicable to common stockholders $ 99,937 $ (73,169 ) $ (62,967 ) Shares used in computation: Weighted-average common shares outstanding 33,427 29,878 26,409 Stock options 3,186 — — Restricted stock units 32 — — Employee stock purchase plan 3 — — Weighted-average diluted common shares 36,648 29,878 26,409 Diluted net income (loss) per share $ 2.73 $ (2.45 ) $ (2.38 )
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): Years Ended December 31, 2018 2017 2016 Stock options issued and outstanding 928 5,468 5,118 Unvested restricted stock units outstanding — 40 40 Employee stock purchase plan — 20 22 928 5,528 5,180

Supplemental Disclosures (Table

Supplemental Disclosures (Tables)	12 Months Ended
	Dec. 31, 2018
Payables And Accruals [Abstract]
Schedules of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consists of the following (in thousands): December 31, 2018 December 31, 2017 Accrued personnel costs $ 9,484 $ 5,789 Accrued external research and development expenses 4,274 2,072 Accrued licensing costs 1,617 — Accrued external general and administrative expenses 773 1,078 Accrued income taxes payable 726 — Accrued purchases of property and equipment 221 430 Other accrued expenses and current liabilities 69 236 $ 17,164 $ 9,605

Selected Quarterly Financial _2

Selected Quarterly Financial Information (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information	Quarters Ended March 31, 2018 June 30, 2018 September 30, 2018 December 31, 2018 Total revenues $ 132,391 $ 40,031 $ 5,306 $ 40,777 Total costs of revenues $ 2,408 $ 3,872 $ 517 $ 2,843 Research and development expense $ 19,550 $ 21,486 $ 18,508 $ 24,329 General and administrative expense $ 8,380 $ 8,318 $ 9,008 $ 11,144 Total operating expenses $ 30,366 $ 33,681 $ 28,031 $ 38,327 Net income (loss) $ 104,239 $ 10,594 $ (19,202 ) $ 4,306 Basic net income (loss) per share $ 3.30 $ 0.33 $ (0.56 ) $ 0.12 Diluted net income (loss) per share $ 3.04 $ 0.30 $ (0.56 ) $ 0.11 Quarters Ended March 31, 2017 June 30, 2017 September 30, 2017 December 31, 2017 Total revenues $ 455 $ 6,562 $ 1,336 $ 2,040 Total costs of revenues $ 91 $ 1,317 $ 683 $ (382 ) Research and development expense $ 16,619 $ 13,917 $ 12,518 $ 14,170 General and administrative expense $ 6,622 $ 6,355 $ 9,444 $ 4,808 Total operating expenses $ 23,377 $ 21,618 $ 22,645 $ 18,638 Net income (loss) $ (21,993 ) $ (14,473 ) $ (20,706 ) $ (15,997 ) Basic net income (loss) per share $ (0.82 ) $ (0.47 ) $ (0.67 ) $ (0.51 ) Diluted net income (loss) per share $ (0.82 ) $ (0.47 ) $ (0.67 ) $ (0.51 )

Nature of Business - Additional

Nature of Business - Additional Information (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Accumulated deficit	$ (83,016)	$ (187,756)
Cash, cash equivalents and marketable securities	$ 470,600

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail)	3 Months Ended								12 Months Ended
	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2018USD ($)Segment	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Jan. 01, 2018USD ($)
Significant Accounting Policies [Line Items]
Number of operating segments | Segment									1
Allowance for doubtful accounts receivable	$ 0				$ 0				$ 0	$ 0
Impairment losses									$ 0	0	$ 0
Percentage of ownership interest	20.00%								20.00%
Other-than-temporary impairment losses									$ 0
Accrued interest or penalties related to uncertain tax positions	$ 0				0				0	0
Unrecognized tax benefits									0	0
Accumulated deficit	(83,016,000)				(187,756,000)				(83,016,000)	(187,756,000)
Interest income from licensing									8,946,000
License revenue	40,777,000	$ 5,306,000	$ 40,031,000	$ 132,391,000	2,040,000	$ 1,336,000	$ 6,562,000	$ 455,000	218,505,000	10,393,000	4,589,000
Deferred revenue	3,933,000								3,933,000
Property and equipment, net	28,702,000				$ 13,977,000				28,702,000	13,977,000
Financing lease obligation	5,854,000								5,854,000
License [Member]
Significant Accounting Policies [Line Items]
License revenue									218,505,000	$ 10,385,000	$ 4,303,000
License [Member] | Ave Xis Incorporation and AbeonaTherapeutics Incorporation [Member]
Significant Accounting Policies [Line Items]
License revenue									12,400,000
ASU 2014-09 [Member]
Significant Accounting Policies [Line Items]
Accumulated deficit												$ (182,953,000)
ASU 2016-02 [Member] | Construction in Progress [Member] | 9800 Medical Center Drive Lease [Member]
Significant Accounting Policies [Line Items]
Property and equipment, net	5,900,000								5,900,000
Financing lease obligation	5,900,000								5,900,000
Reduction in Accumulated Deficit [Member] | ASU 2014-09 [Member]
Significant Accounting Policies [Line Items]
Accumulated deficit	(1,772,000)								(1,772,000)			$ 4,803,000
Interest income from licensing									8,946,000
Deferred revenue	3,900,000								3,900,000
Reduction in Accumulated Deficit [Member] | ASU 2014-09 [Member] | License [Member]
Significant Accounting Policies [Line Items]
License revenue									(16,647,000)
Results Without Adoption of Topic 606
Significant Accounting Policies [Line Items]
Interest income from licensing									0
Results Without Adoption of Topic 606 | License [Member]
Significant Accounting Policies [Line Items]
License revenue									3,900,000
Results Without Adoption of Topic 606 | ASU 2014-09 [Member]
Significant Accounting Policies [Line Items]
Accumulated deficit	$ (81,244,000)								(81,244,000)
Results Without Adoption of Topic 606 | ASU 2014-09 [Member] | License [Member]
Significant Accounting Policies [Line Items]
License revenue									$ 235,152,000
Customer Concentration Risk [Member] | United States [Member] | Revenue [Member]
Significant Accounting Policies [Line Items]
Concentration risk percentage									99.00%	96.00%	90.00%

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Summary of Reconciliation of Cash and Cash Equivalents and Restricted Cash (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Cash and cash equivalents	$ 75,561	$ 46,656	$ 24,840
Restricted cash	1,053	225	225
Total cash and cash equivalents and restricted cash	$ 76,614	$ 46,881	$ 25,065

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Schedule of Revenue or Accounts Receivable by Major Customers (Detail) - Customer Concentration Risk [Member]	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue [Member] | Customer A [Member]
Entity Wide Revenue Major Customer [Line Items]
Concentration risk percentage	81.00%	68.00%
Revenue [Member] | Customer B [Member]
Entity Wide Revenue Major Customer [Line Items]
Concentration risk percentage	16.00%
Revenue [Member] | Customer C [Member]
Entity Wide Revenue Major Customer [Line Items]
Concentration risk percentage			24.00%
Revenue [Member] | Customer F [Member]
Entity Wide Revenue Major Customer [Line Items]
Concentration risk percentage			44.00%
Accounts Receivable | Customer B [Member]
Entity Wide Revenue Major Customer [Line Items]
Concentration risk percentage	82.00%
Accounts Receivable | Customer D [Member]
Entity Wide Revenue Major Customer [Line Items]
Concentration risk percentage		42.00%
Accounts Receivable | Customer E [Member]
Entity Wide Revenue Major Customer [Line Items]
Concentration risk percentage		32.00%
Accounts Receivable | Customer G [Member]
Entity Wide Revenue Major Customer [Line Items]
Concentration risk percentage		21.00%

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Summary of Estimated Useful Lives of Assets (Detail)	12 Months Ended
	Dec. 31, 2018
Computer Equipment and Software [Member]
Property Plant And Equipment [Line Items]
Property plant and equipment estimated useful lives	3 years
Lab Equipment [Member]
Property Plant And Equipment [Line Items]
Property plant and equipment estimated useful lives	5 years
Furniture and Fixtures [Member]
Property Plant And Equipment [Line Items]
Property plant and equipment estimated useful lives	5 years
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Property plant and equipment estimated useful lives	Shorter of lease term or estimated useful life

Summary of Significant Accoun_8

Summary of Significant Accounting Policies - Schedule of Impact on Consolidated Balance Sheet on Adoption of Topic 606 (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets
Accounts receivable, current	$ 8,587		$ 473
Accounts receivable, non-current	23,012
Prepaid expenses	5,734		5,334
Other current assets	3,831		1,412
Other assets	2,315		862
Liabilities:
Accrued expenses and other current liabilities	17,164		9,605
Deferred revenue, current	600
Deferred revenue, non-current	3,333
Other liabilities	2,505
Stockholders’ equity
Accumulated deficit	(83,016)		$ (187,756)
ASU 2014-09 [Member]
Assets
Accounts receivable, current		$ 1,000
Accounts receivable, non-current		4,850
Other current assets		1,762
Liabilities:
Accrued expenses and other current liabilities		9,710
Other liabilities		819
Stockholders’ equity
Accumulated deficit		(182,953)
Cumulative Adjustment for Adoption of Topic 606 [Member] | ASU 2014-09 [Member]
Assets
Accounts receivable, current	(1,803)	527
Accounts receivable, non-current	3,012	4,850
Prepaid expenses	60
Other current assets	750	350
Other assets	267
Liabilities:
Accrued expenses and other current liabilities	(580)	105
Deferred revenue, current	600
Deferred revenue, non-current	3,333
Other liabilities	705	819
Stockholders’ equity
Accumulated deficit	(1,772)	$ 4,803
Results Without Adoption of Topic 606 | ASU 2014-09 [Member]
Assets
Accounts receivable, current	10,390
Accounts receivable, non-current	20,000
Prepaid expenses	5,674
Other current assets	3,081
Other assets	2,048
Liabilities:
Accrued expenses and other current liabilities	17,744
Other liabilities	1,800
Stockholders’ equity
Accumulated deficit	$ (81,244)

Summary of Significant Accoun_9

Summary of Significant Accounting Policies - Schedule of Impact on Consolidated Statement of Operations on Adoption of Topic 606 (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues
License revenue	$ 40,777	$ 5,306	$ 40,031	$ 132,391	$ 2,040	$ 1,336	$ 6,562	$ 455	$ 218,505	$ 10,393	$ 4,589
Other Income
Interest income from licensing									8,946
Income Tax Expense									(4,179)	0	435
Net Income	$ 4,306	$ (19,202)	$ 10,594	$ 104,239	$ (15,997)	$ (20,706)	$ (14,473)	$ (21,993)	$ 99,937	$ (73,169)	$ (62,967)
Net Income Per Share:
Basic	$ 0.12	$ (0.56)	$ 0.33	$ 3.30	$ (0.51)	$ (0.67)	$ (0.47)	$ (0.82)	$ 2.99	$ (2.45)	$ (2.38)
Diluted	$ 0.11	$ (0.56)	$ 0.30	$ 3.04	$ (0.51)	$ (0.67)	$ (0.47)	$ (0.82)	$ 2.73	$ (2.45)	$ (2.38)
License [Member]
Revenues
License revenue									$ 218,505	$ 10,385	$ 4,303
Operating Expenses
Licensing costs									9,640	$ 1,703	$ 861
Cumulative Adjustment for Adoption of Topic 606 [Member] | ASU 2014-09 [Member]
Other Income
Interest income from licensing									8,946
Income Tax Expense									730
Net Income									$ (6,575)
Net Income Per Share:
Basic									$ (0.20)
Diluted									$ (0.18)
Cumulative Adjustment for Adoption of Topic 606 [Member] | License [Member] | ASU 2014-09 [Member]
Revenues
License revenue									$ (16,647)
Operating Expenses
Licensing costs									(396)
Results Without Adoption of Topic 606
Other Income
Interest income from licensing									0
Results Without Adoption of Topic 606 | ASU 2014-09 [Member]
Other Income
Income Tax Expense									(4,909)
Net Income									$ 106,512
Net Income Per Share:
Basic									$ 3.19
Diluted									$ 2.91
Results Without Adoption of Topic 606 | License [Member]
Revenues
License revenue									$ 3,900
Results Without Adoption of Topic 606 | License [Member] | ASU 2014-09 [Member]
Revenues
License revenue									235,152
Operating Expenses
Licensing costs									$ 10,036

Summary of Significant Accou_10

Summary of Significant Accounting Policies - Schedule of Impact on Consolidated Statement of Cash Flows on Adoption of Topic 606 (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash Flows from Operating Activities:
Net income	$ 99,937	$ (73,169)	$ (62,967)
Imputed interest income from licensing	(8,946)
Changes in accounts receivable	(16,803)	561	1,073
Changes in prepaid expenses	(400)	(3,559)	(755)
Changes in other current assets	(2,069)	(402)	(159)
Changes in other assets	(1,453)	(135)	(139)
Changes in accrued expenses and other current liabilities	7,582	$ 1,897	$ 3,873
Changes in deferred revenue	3,933
Changes in other liabilities	1,686
Cumulative Adjustment for Adoption of Topic 606 [Member] | ASU 2014-09 [Member]
Cash Flows from Operating Activities:
Net income	(6,575)
Imputed interest income from licensing	(8,946)
Changes in accounts receivable	13,114
Changes in prepaid expenses	(60)
Changes in other current assets	(400)
Changes in other assets	(267)
Changes in accrued expenses and other current liabilities	(685)
Changes in deferred revenue	3,933
Changes in other liabilities	(114)
Results Without Adoption of Topic 606 | ASU 2014-09 [Member]
Cash Flows from Operating Activities:
Net income	106,512
Changes in accounts receivable	(29,917)
Changes in prepaid expenses	(340)
Changes in other current assets	(1,669)
Changes in other assets	(1,186)
Changes in accrued expenses and other current liabilities	8,267
Changes in other liabilities	$ 1,800

Marketable Securities - Summary

Marketable Securities - Summary of Company Marketable Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 395,304	$ 130,018
Unrealized Gains	129	2
Unrealized Losses	(414)	(282)
Fair Value	395,019	129,738
U.S. Government and Federal Agency Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	103,410
Unrealized Gains	93
Unrealized Losses	(37)
Fair Value	103,466
Certificates of Deposit [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	8,992
Fair Value	8,992
Corporate Bonds [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	282,902	130,018
Unrealized Gains	36	2
Unrealized Losses	(377)	(282)
Fair Value	$ 282,561	$ 129,738

Marketable Securities - Additio

Marketable Securities - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2018USD ($)Security	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Schedule Of Available For Sale Securities [Line Items]
Available for sale securities remaining maturities greater than three years	$ 0	$ 0
Unrealized gains (losses) on available-for-sale securities, income tax expense	0	0	$ 400,000
Net realized gains or losses available for sale securities	$ (39,000)	479,000
Number of investment grade fixed income security | Security	102
Other-than-temporary impaired	$ 0	0
Maximum [Member]
Schedule Of Available For Sale Securities [Line Items]
Unrealized gains (losses) on available-for-sale securities, before tax	(100,000)	(200,000)	1,100,000
Debt Securities [Member] | Investment Income [Member] | Maximum [Member]
Schedule Of Available For Sale Securities [Line Items]
Net realized gains or losses available for sale securities	$ (100,000)	$ 500,000	$ (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	Dec. 31, 2018	Dec. 31, 2017
Schedule Of Available For Sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 298,407
Less than 12 Months, Unrealized Losses	(391)	$ (180)
12 Months or Greater, Fair Value	12,424
12 Months or Greater, Unrealized Losses	(23)	(102)
Total, Fair Value	310,831
Total, Unrealized Losses	(414)	(282)
Less than 12 Months, Fair Value		109,238
12 Months or Greater, Fair Value		17,124
Total, Fair Value		126,362
U.S. Government and Federal Agency Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than 12 Months, Fair Value	53,124
Less than 12 Months, Unrealized Losses	(37)
Total, Fair Value	53,124
Total, Unrealized Losses	(37)
Corporate Bonds [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than 12 Months, Fair Value	245,283
Less than 12 Months, Unrealized Losses	(354)	(180)
12 Months or Greater, Fair Value	12,424
12 Months or Greater, Unrealized Losses	(23)	(102)
Total, Fair Value	257,707
Total, Unrealized Losses	$ (377)	(282)
Less than 12 Months, Fair Value		109,238
12 Months or Greater, Fair Value		17,124
Total, Fair Value		$ 126,362

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	Dec. 31, 2018	Dec. 31, 2017
Marketable securities:
Fair Value	$ 395,019	$ 129,738
Cash Equivalents and Marketable Securities [Member]
Marketable securities:
Total cash equivalents and marketable securities	470,561	176,384
Corporate Bonds [Member]
Marketable securities:
Fair Value	282,561	129,738
Cash Equivalents [Member]
Cash equivalents:
Total cash equivalents	75,542	46,646
U.S. Government and Federal Agency Securities [Member]
Marketable securities:
Fair Value	103,466
Certificates of Deposit [Member]
Marketable securities:
Fair Value	8,992
Money Market Mutual Funds [Member] | Cash Equivalents [Member]
Cash equivalents:
Total cash equivalents	75,542	46,646
Significant Other Observable Inputs (Level 2) [Member]
Marketable securities:
Fair Value	395,019	129,738
Significant Other Observable Inputs (Level 2) [Member] | Cash Equivalents and Marketable Securities [Member]
Marketable securities:
Total cash equivalents and marketable securities	470,561	176,384
Significant Other Observable Inputs (Level 2) [Member] | Corporate Bonds [Member]
Marketable securities:
Fair Value	282,561	129,738
Significant Other Observable Inputs (Level 2) [Member] | Cash Equivalents [Member]
Cash equivalents:
Total cash equivalents	75,542	46,646
Significant Other Observable Inputs (Level 2) [Member] | U.S. Government and Federal Agency Securities [Member]
Marketable securities:
Fair Value	103,466
Significant Other Observable Inputs (Level 2) [Member] | Certificates of Deposit [Member]
Marketable securities:
Fair Value	8,992
Significant Other Observable Inputs (Level 2) [Member] | Money Market Mutual Funds [Member] | Cash Equivalents [Member]
Cash equivalents:
Total cash equivalents	$ 75,542	$ 46,646

Fair Value of Financial Instr_4

Fair Value of Financial Instruments - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
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	400,000
Remeasurements or impairment losses on non-marketable equity securities	$ 0	$ 0	$ 0

Property and Equipment Net - Sc

Property and Equipment Net - Schedule of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property Plant And Equipment [Line Items]
Total property and equipment	$ 35,939	$ 17,254
Accumulated depreciation and amortization	(7,237)	(3,277)
Property and equipment, net	28,702	13,977
Lab Equipment [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	14,417	8,561
Computer Equipment and Software [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	2,002	1,481
Furniture and Fixtures [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	1,915	1,384
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	11,751	$ 5,828
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 ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Line Items]
Total property and equipment	$ 35,939,000	$ 17,254,000
Depreciation or amortization expense	3,982,000	$ 2,686,000	$ 544,000
Construction in Progress [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	5,854,000
Construction in Progress [Member] | 9800 Medical Center Drive Lease [Member] | Maximum [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	$ 100,000

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail)	1 Months Ended				12 Months Ended			118 Months Ended
	Nov. 30, 2018USD ($)ft²	Jan. 31, 2016USD ($)	Sep. 30, 2015USD ($)	Mar. 31, 2015	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2018USD ($)	Mar. 31, 2009USD ($)
Other Commitments [Line Items]
Tenant improvement allowance received			$ 400,000
Leases, rent expense, net					$ 2,800,000	$ 1,800,000	$ 1,800,000
Claims paid to date related to indemnification issues					0
Accruals or expenses related to indemnification issues					0	0
European Patent Office Proceeding [Member]
Other Commitments [Line Items]
Liability related to third party opposition					0	0		$ 0
The Trustees of the University of Pennsylvania [Member]
Other Commitments [Line Items]
Accrued expenses					100,000			100,000
GlaxoSmithKline LLC [Member]
Other Commitments [Line Items]
Accrued expenses					$ 4,100,000	300,000		4,100,000
Milestone payment obligation									$ 1,500,000
GlaxoSmithKline LLC [Member] | Milestone Fees [Member]
Other Commitments [Line Items]
Related party transaction expense								500,000
Maximum [Member] | The Trustees of the University of Pennsylvania [Member]
Other Commitments [Line Items]
Accrued expenses						$ 100,000
Rockville, Maryland [Member]
Other Commitments [Line Items]
Lease term commenced date		2016-02		2015-04
Lease term					September 2015, November 2015 and July 2017: Ultimately extend the term of the lease to September 2021.
Options to extend the additional lease term			6 years
Tenant improvement allowance received		$ 800,000
Lease period		7 years 6 months
Lease expiration date		Sep. 30, 2023
Options to extend the lease		5 years
Monthly lease payments commencement period		2016-09
Operating leases expiration year					2,021
New York, New York [Member]
Other Commitments [Line Items]
Letters of credit					$ 200,000			$ 200,000
9800 Medical Center Drive Lease [Member] | Rockville, Maryland [Member]
Other Commitments [Line Items]
Number of square feet to be constructed | ft²	132,000
Construction completion, description					Construction of the new building, which will be conducted by the landlord, is expected to be completed in 2020
Lease term, from the delivery of leased premises	16 years
Lease term, description					the lease will expire approximately 16 years from the delivery of the leased premises to the Company, subject to certain extension and termination options. Under the terms of the 9800 Medical Center Drive Lease, the Company will receive a $14.6 million tenant improvement allowance from the landlord to construct additional improvements to the leased premises.
Tenant improvement allowance to be received	$ 14,600,000
Option to extend the lease	true
Additional option to extend the lease, term	10 years
Option to terminate the lease	true
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. Additionally, after 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.
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

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Future Minimum Lease Payments Under 9800 Medical Center Drive Lease and Other Operating Leases (Detail) $ in Thousands	Dec. 31, 2018USD ($)
Other Commitments [Line Items]
2,019	$ 2,798
2,020	3,054
2,021	3,720
2,022	4,910
2,023	5,635
Thereafter	76,420
Total minimum lease payments	96,537
9800 Medical Center Drive Lease [Member]
Other Commitments [Line Items]
2,021	1,329
2,022	4,289
2,023	5,156
Thereafter	76,420
Total minimum lease payments	87,194
Other Operating leases [Member]
Other Commitments [Line Items]
2,019	2,798
2,020	3,054
2,021	2,391
2,022	621
2,023	479
Total minimum lease payments	$ 9,343

Commitments and Contingencies_3

Commitments and Contingencies - Summary of Expenses Incurred by Company (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
GlaxoSmithKline LLC [Member]
Other Commitments [Line Items]
Total related party transaction expense	$ 9,955	$ 2,008	$ 1,034
GlaxoSmithKline LLC [Member] | Licensing Costs [Member]
Other Commitments [Line Items]
Total related party transaction expense	9,407	1,497	430
GlaxoSmithKline LLC [Member] | Other Costs Of Revenue
Other Commitments [Line Items]
Total related party transaction expense		2	7
GlaxoSmithKline LLC [Member] | General and Administrative [Member]
Other Commitments [Line Items]
Total related party transaction expense	548	509	597
License Fees [Member] | The Trustees of the University of Pennsylvania [Member]
Other Commitments [Line Items]
Total related party transaction expense	112	444	574
License Fees [Member] | The Trustees of the University of Pennsylvania [Member] | Licensing Costs [Member]
Other Commitments [Line Items]
Total related party transaction expense	(18)	207	430
License Fees [Member] | The Trustees of the University of Pennsylvania [Member] | Other Costs Of Revenue
Other Commitments [Line Items]
Total related party transaction expense		4	11
License Fees [Member] | The Trustees of the University of Pennsylvania [Member] | General and Administrative [Member]
Other Commitments [Line Items]
Total related party transaction expense	$ 130	$ 233	$ 133

Capitalization - Additional Inf

Capitalization - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		12 Months Ended
	Aug. 31, 2018	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Schedule of Capitalization [Line Items]
Common stock, shares authorized			100,000,000	100,000,000
Common stock, par value			$ 0.0001	$ 0.0001
Preferred stock, shares authorized			10,000,000	10,000,000
Preferred stock, par value			$ 0.0001	$ 0.0001
Net proceeds from issuance of common stock			$ 189,716	$ 81,994
Common Stock [Member]
Schedule of Capitalization [Line Items]
Number of shares issued to during period			3,105,000	4,255,000
Public Offering [Member]
Schedule of Capitalization [Line Items]
Number of shares issued to during period	3,105,000	3,700,000
Stock issuance price per share	$ 65	$ 20.50
Net proceeds from issuance of common stock	$ 189,100	$ 81,500
Overallotment Option [Member] | Common Stock [Member]
Schedule of Capitalization [Line Items]
Number of shares issued to during period	405,000	555,000

Capitalization - Schedule of Re

Capitalization - Schedule of Reserved Shares of Common Stock for Future Issuance (Detail) - shares shares in Thousands	Dec. 31, 2018	Dec. 31, 2017
Schedule of Capitalization [Line Items]
Reserved common shares	7,169	7,636
Equity Incentive Plans [Member]
Schedule of Capitalization [Line Items]
Reserved common shares	6,999	7,430
Employee Stock Purchase Plan [Member]
Schedule of Capitalization [Line Items]
Reserved common shares	170	206

License Revenue - Additional In

License Revenue - Additional Information (Detail)	1 Months Ended					3 Months Ended								12 Months Ended
	Nov. 30, 2018USD ($)	May 31, 2018USD ($)	Jan. 31, 2018USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2014USD ($)	Dec. 31, 2018USD ($)ProductCandidateTechnologyLicensee	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2018USD ($)ProductCandidateTechnologyLicensee	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
License Revenue [Line Items]
Milestone payment upon commencement of clinical trials in humans														$ 30,400,000
Milestone payment upon submission of regulatory approval filings														47,500,000
Milestone payment upon approval of commercial products by regulatory agencies														117,500,000
Milestone payment upon achievement of specified sales targets for licensed products														232,000,000
Deferred revenue						$ 3,933,000								3,933,000
License revenue						40,777,000	$ 5,306,000	$ 40,031,000	$ 132,391,000	$ 2,040,000	$ 1,336,000	$ 6,562,000	$ 455,000	218,505,000	$ 10,393,000	$ 4,589,000
Impirment losses on receivables or contract assets														0
Total current and non-current accounts receivable						31,599,000				5,850,000				31,599,000	5,850,000
Billed to customers						400,000								400,000
Billable to customers in future periods						31,200,000								$ 31,200,000
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 December 31, 2018, 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, if any.
Interest income from licensing														$ 8,946,000
Accounts receivable, current						8,587,000				473,000				8,587,000	473,000
Accounts receivable, non -current						$ 23,012,000								23,012,000
Abeona Therapeutics Inc [Member]
License Revenue [Line Items]
Upfront and annual fees upon termination of license agreement	$ 40,000,000
Remaining unpaid portion of upfront and annual fees	120,000,000
Sales-based milestone payments	60,000,000
Maximum [Member] | Abeona Therapeutics Inc [Member]
License Revenue [Line Items]
Up-front and anuual fees	120,000,000
License [Member]
License Revenue [Line Items]
License revenue														$ 218,505,000	10,385,000	4,303,000
NAV Technology Licensees [Member] | NAV Technology Platform [Member]
License Revenue [Line Items]
Number of technology licensees | TechnologyLicensee						11								11
NAV Technology Licensees [Member] | NAV Technology Platform [Member] | Minimum [Member]
License Revenue [Line Items]
Number of development partnered product candidates | ProductCandidate						20								20
November 2018 License Agreement [Member] | Abeona Therapeutics Inc [Member]
License Revenue [Line Items]
Accounts receivable						$ 26,000,000								$ 26,000,000
Transaction price of license	35,600,000
Sales-based milestone payment exclude transaction price														$ 60,000,000
Consideration payment due period one														2019-11
Consideration payment due period two														2020-11
Transaction price description														Upon its execution, and as of December 31, 2018, the transaction price of the November 2018 license agreement with Abeona was $35.6 million, which was fully recognized as license revenue upon the delivery of the licenses in November 2018. The transaction price includes the following fixed consideration payable to the Company over the initial contract term of three years: (i) the $10.0 million payment in November 2018 and (ii) the present value, as of the date of the license agreement, of the $10.0 million payment due in November 2019 and $20.0 million payment due in November 2020. The discounted portion of the annual payments represents the financing benefit provided to Abeona and is recognized as interest income from licensing over the financing term of two years. Variable consideration under the license agreement, which has been excluded from the transaction price, includes the sales-based milestone payments of $60.0 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, if any. The annual payments due under the agreement beginning in November 2021 represent contract renewal options granted to Abeona for revenue recognition purposes, and therefore are excluded from the transaction price. If renewed by Abeona, each of these payments will be recognized as revenue on the first day of the license renewal period for which the payment relates to, which is the date the payments are due under the agreement.
Interest income from licensing														$ 400,000
Accounts receivable, current						7,500,000								7,500,000
Accounts receivable, non -current						18,500,000								$ 18,500,000
License agreement initial contract term														3 years
Upfront payment received	10,000,000
License agreement financing term														2 years
November 2018 License Agreement [Member] | Abeona Therapeutics Inc [Member] | First Anniversary [Member]
License Revenue [Line Items]
Payments due from related party						10,000,000								$ 10,000,000
November 2018 License Agreement [Member] | Abeona Therapeutics Inc [Member] | Second Anniversary [Member]
License Revenue [Line Items]
Payments due from related party						20,000,000								20,000,000
November 2018 License Agreement [Member] | License [Member] | Abeona Therapeutics Inc [Member]
License Revenue [Line Items]
Accounts receivable						26,000,000								26,000,000
License revenue														35,600,000
License Agreement [Member] | License [Member]
License Revenue [Line Items]
License revenue														5,300,000
March 2014 License Agreement [Member]
License Revenue [Line Items]
Accounts receivable										0					0
Up-front fee paid														2,000,000
Transaction price of license						7,500,000								7,500,000
Payments for remaining development milestones						7,000,000								7,000,000
March 2014 License Agreement [Member] | AveXis, Inc. [Member]
License Revenue [Line Items]
Accounts receivable						200,000								200,000
Up-front fee paid					$ 2,000,000
Milestone fee payments upon achievement of various development and commercialization					$ 12,300,000
License agreement amendment date					2018-01
Interest income from licensing														8,000,000
Accounts receivable, non -current						200,000								200,000
March 2014 License Agreement [Member] | Maximum [Member] | AveXis, Inc. [Member]
License Revenue [Line Items]
Accounts receivable, current						100,000								100,000
March 2014 License Agreement [Member] | License [Member]
License Revenue [Line Items]
License revenue															1,100,000	$ 100,000
March 2014 License Agreement [Member] | License [Member] | AveXis, Inc. [Member]
License Revenue [Line Items]
License revenue														176,100,000
January 2018 Amendment Agreement [Member]
License Revenue [Line Items]
License fee			$ 80,000,000
Sales-based milestone payment unpaid in the event of change of control			40,000,000
Transaction price of license			132,100,000			172,100,000								172,100,000
Sales-based milestone payment exclude transaction price														80,000,000
Payments due from related party						30,000,000								$ 30,000,000
Consideration payment due period one														2019-01
Consideration payment due period two														2020-01
Interest income from licensing		$ 6,100,000
January 2018 Amendment Agreement [Member] | Share-based Milestone [Member]
License Revenue [Line Items]
Increase in transaction price of license		40,000,000
January 2018 Amendment Agreement [Member] | First Anniversary [Member]
License Revenue [Line Items]
License fee			30,000,000
January 2018 Amendment Agreement [Member] | Second Anniversary [Member]
License Revenue [Line Items]
License fee			$ 30,000,000
January 2018 Amendment Agreement [Member] | AveXis, Inc. [Member]
License Revenue [Line Items]
License agreement period			14 years
License fees received		100,000,000
January 2018 Amendment Agreement [Member] | Minimum [Member]
License Revenue [Line Items]
Milestone payment			$ 120,000,000
January 2018 Amendment Agreement [Member] | License [Member]
License Revenue [Line Items]
Increase in transaction price of license		$ 40,000,000
June 2017 License Agreement [Member] | AveXis, Inc. [Member]
License Revenue [Line Items]
Accounts receivable						800,000				$ 0				$ 800,000	0
Up-front fee paid				$ 6,000,000
Milestone fee payments upon achievement of various development and commercialization				$ 36,000,000
Interest income from licensing														100,000
Accounts receivable, current						100,000								100,000
Accounts receivable, non -current						$ 700,000								700,000
June 2017 License Agreement [Member] | License [Member] | AveXis, Inc. [Member]
License Revenue [Line Items]
License revenue														$ 0	$ 6,000,000
November 2018 [Member] | Abeona Therapeutics Inc [Member]
License Revenue [Line Items]
Up-front and anuual fees	10,000,000
November 2019 [Member] | Abeona Therapeutics Inc [Member]
License Revenue [Line Items]
Up-front and anuual fees	10,000,000
November 2020 [Member] | Abeona Therapeutics Inc [Member]
License Revenue [Line Items]
Up-front and anuual fees	20,000,000
November 2021 [Member] | Abeona Therapeutics Inc [Member]
License Revenue [Line Items]
Up-front and anuual fees	20,000,000
November 2022 [Member] | Abeona Therapeutics Inc [Member]
License Revenue [Line Items]
Up-front and anuual fees	20,000,000
November 2023 [Member] | Abeona Therapeutics Inc [Member]
License Revenue [Line Items]
Up-front and anuual fees	20,000,000
November 2024 [Member] | Abeona Therapeutics Inc [Member]
License Revenue [Line Items]
Up-front and anuual fees	$ 20,000,000

License Revenue - Summary of Ch

License Revenue - Summary of Changes in Balances of Receivables, Contract Assets and Contract Liabilities (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)
Receivables and contract assets:
Accounts receivable, current and non-current, Balance at Beginning of Period	$ 5,850
Accounts receivable, current and non-current, Net Additions (Deductions)	25,749
Accounts receivable, current and non-current, Balance at End of Period	31,599
Contract assets, Balance at Beginning of Period	350
Contract assets, Net Additions (Deductions)	400
Contract assets, Balance at End of Period	750
Contract liabilities:
Changes in deferred revenue	3,933
Deferred revenue, current and non-current, Balance at End of Period	$ 3,933

License Revenue - Additional _2

License Revenue - Additional Information (Detail1)	Dec. 31, 2018
January 2018 Amendment Agreement [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
November 2018 License Agreement [Member] | Abeona Therapeutics Inc [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2018-11-01
License Revenue [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, period	2 years

Stock-based Compensation - Addi

Stock-based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Sep. 16, 2015	Jan. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jul. 01, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation expense			$ 41,600
Unrecognized stock-based compensation, weighted-average period			2 years 8 months 12 days
Proceeds from exercise of stock options			$ 14,499	$ 2,493	$ 179
Stock-based compensation expense			$ 16,641	$ 10,605	$ 7,031
2015 Equity Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of annual increase in number of shares available for future issuance			4.00%
Common stock shares authorized for issuance			9,488,413
Shares available for future grants			2,104,070
Stock options expiration date			10 years
Stock options vesting period			4 years
Stock plan expiration date			2025-06
Weighted-average fair values of options granted			$ 27.49	$ 13.87	$ 8.37
Exercise of stock options, Shares			1,684,522	515,916	163,158
Total intrinsic value of options exercised			$ 68,200	$ 11,100	$ 1,700
2015 Equity Incentive Plan [Member] | Non-Employee Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense				$ 500	$ 600
Unvested stock options outstanding						0
2015 Equity Incentive Plan [Member] | Subsequent Event [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Additional shares to be issued		1,444,808
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			169,580
Share-based compensation arrangement by share-based payment award, description			The number of authorized shares reserved for issuance under the 2015 ESPP automatically increases on the first business day of each fiscal year
Share-based compensation arrangement by share-based payment award, percentage of outstanding stock minimum	1.00%
Common stock shares issued to participants			36,700	47,720	0

Stock-based Compensation - Stoc

Stock-based Compensation - Stock-Based Compensation Expense by Award Type (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 16,641	$ 10,605	$ 7,031
Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	15,960	10,031	6,950
Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	275	275	23
Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 406	$ 299	$ 58

Stock-based Compensation - St_2

Stock-based Compensation - Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 16,641	$ 10,605	$ 7,031
Research and Development Costs [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	7,612	5,128	2,743
General and Administrative [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 9,029	$ 5,477	$ 4,288

Stock-based Compensation - Summ

Stock-based Compensation - Summary of Stock Option Activity (Detail) - 2014 and 2015 Equity Incentive Plan [Member] - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares [Roll Forward]
Shares Outstanding, Beginning Balance	5,468
Shares, Granted	1,397
Shares, Exercised	(1,685)
Shares, Cancelled or forfeited	(325)
Shares Outstanding, Ending Balance	4,855	5,468
Shares, Exercisable	2,535
Shares, Vested and expected to vest	4,855
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted-average Exercise Price Outstanding, Beginning Balance	$ 10.25
Weighted-average Exercise Price, Granted	41.11
Weighted-average Exercise Price, Exercised	8.63
Weighted-average Exercise Price, Cancelled or forfeited	15.95
Weighted-average Exercise Price, Outstanding, Ending Balance	19.31	$ 10.25
Weighted-average Exercise Price, Exercisable	9.15
Weighted-average Exercise Price, Vested and expected to vest	$ 19.31
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted-average Remaining Contractual Life (Years) Outstanding	7 years 7 months 6 days	7 years 10 months 24 days
Weighted-average Remaining Contractual Life (Years), Exercisable	6 years 8 months 12 days
Weighted-average Remaining Contractual Life (Years), Vested and expected to vest	7 years 7 months 6 days
Aggregate Intrinsic Value Outstanding	$ 118,185	$ 125,738
Aggregate Intrinsic Value, Exercisable	83,529
Aggregate Intrinsic Value, Vested and expected to vest	$ 118,185

Stock-based Compensation - Sche

Stock-based Compensation - Schedule of Fair Value of Options Granted on Weighted-Average Assumptions (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions And Methodology [Abstract]
Expected volatility	75.00%	77.00%	75.00%
Expected term (in years)	6 years	6 years 2 months 12 days	6 years 2 months 12 days
Risk-free interest rate	2.60%	2.10%	1.50%
Expected dividend yield	0.00%	0.00%	0.00%

Stock-based Compensation - Su_2

Stock-based Compensation - Summary of Unvested RSUs Activity Under 2015 Plan (Detail) - Restricted Stock Units [Member] shares in Thousands	12 Months Ended
	Dec. 31, 2018$ / 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

Retirement Plan - Additional In

Retirement Plan - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Compensation And Retirement Disclosure [Abstract]
Employer matching contribution expense	$ 1.3	$ 1	$ 0.6

Income Taxes - Components of In

Income Taxes - Components of Income (Loss) Before Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
United States	$ 104,181	$ (73,138)	$ (63,402)
Foreign	(65)	(31)
Income (loss) before income taxes	$ 104,116	$ (73,169)	$ (63,402)

Income Taxes - Components of th

Income Taxes - Components of the Provision For Income Tax Expense (Benefit) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current:
State	$ 4,179
Total current	4,179
Deferred:
Federal			$ (381)
State			(54)
Total deferred			(435)
Total income tax expense (benefit)	$ 4,179	$ 0	$ (435)

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Line Items]
Federal statutory income tax rate, percent	21.00%	34.00%	34.00%
Tax Cuts and Jobs Act of 2017, limitation of net operating losses deductions as percentage of current year taxable income		80.00%
Tax Cuts and Jobs Act of 2017, incomplete accounting change in tax rate deferred tax asset and valuation allowance provisional income tax expense	$ 17,900,000
Cumulative loss position period	3 years
Increase (decrease) in valuation allowance	$ (14,100,000)
Research and development and orphan drug tax credit carryforwards	$ 28,984,000	$ 21,137,000
Tax credit carryforwards, expiration year	2,038
Reserve for uncertain tax positions placed against credit carryforwards	$ 200,000	100,000
Reserve for uncertain tax positions placed against qualified expenses	$ 0	0
Cumulative changes in ownership Interest percentage threshold, subject to annual limitation of NOL and tax credit carryforwards	50.00%
Ownership interest change period	3 years
Domestic Country [Member]
Income Tax Disclosure [Line Items]
Operating loss carryforwards	$ 56,100,000	126,700,000
Operating Loss Carryforwards Expiration Year	2,037
Research and development and orphan drug tax credit carryforwards	$ 29,100,000	21,300,000
U. S State Tax Authority [Member]
Income Tax Disclosure [Line Items]
Operating loss carryforwards	$ 56,200,000	$ 167,800,000
Operating Loss Carryforwards Expiration Year	2,037

Income Taxes - Schedule of Reco

Income Taxes - Schedule of Reconciliation of Effective Income Tax Expense (Benefit) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Federal income tax expense (benefit) at statutory rate	$ 21,862	$ (24,876)	$ (21,556)
State income tax expense (benefit), net of federal tax effect	9,691	(7,756)	(1,617)
Research and development credits	(7,847)	(6,297)	(7,275)
Stock-based compensation expense for incentive stock options and employee stock purchase plan	(6,493)	(3,012)	1,805
Other non-deductible expenses and reconciling items	139	(26)	170
Change in corporate tax rates	(729)	16,598	42
Change in valuation allowance	(12,444)	25,369	27,996
Total income tax expense (benefit)	$ 4,179	$ 0	$ (435)

Income Taxes - Components of Ne

Income Taxes - Components of Net Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Net operating loss carryforwards	$ 15,468	$ 37,658
Research and development tax credits	28,984	21,137
Step-up in assets upon conversion to C-corporation	729	721
Stock-based compensation expense for non-qualified stock options and restricted stock units	5,462	4,263
Unrealized losses on marketable securities	101	89
Deferred rent	495	458
Accruals and other	2,772	1,540
Total deferred tax assets before valuation allowance	54,011	65,866
Valuation allowance	(51,533)	(65,669)
Total deferred tax assets	2,478	197
Deferred tax liabilities:
Depreciation	(1,207)	(197)
Other	(1,271)
Total deferred tax liabilities	(2,478)	(197)
Net deferred tax assets	$ 0	$ 0

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Detail) - Research and Development Costs [Member] - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
FOXKISER,LLP [Member] | Service Agreements [Member]
Related Party Transaction [Line Items]
Related party transaction expense		$ 2.1	$ 1.5	$ 1
Scientific Founder and Special Advisor [Member]
Related Party Transaction [Line Items]
Related party transaction expenses from transactions with related party advisory fees	$ 0.1			$ 0.3

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								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Basic net income (loss) per share:
Net income (loss) applicable to common stockholders									$ 99,937	$ (73,169)	$ (62,967)
Shares used in computation:
Weighted-average common shares outstanding									33,427	29,878	26,409
Basic net income (loss) per share	$ 0.12	$ (0.56)	$ 0.33	$ 3.30	$ (0.51)	$ (0.67)	$ (0.47)	$ (0.82)	$ 2.99	$ (2.45)	$ (2.38)
Diluted net income (loss) per share:
Net income (loss) applicable to common stockholders									$ 99,937	$ (73,169)	$ (62,967)
Shares used in computation:
Weighted-average diluted common shares									36,648	29,878	26,409
Diluted net income (loss) per share	$ 0.11	$ (0.56)	$ 0.30	$ 3.04	$ (0.51)	$ (0.67)	$ (0.47)	$ (0.82)	$ 2.73	$ (2.45)	$ (2.38)
Common Shares [Member]
Shares used in computation:
Weighted-average diluted common shares									33,427	29,878	26,409
Stock Option [Member]
Shares used in computation:
Weighted-average diluted common shares									3,186
Restricted Stock Units [Member]
Shares used in computation:
Weighted-average diluted common shares									32
Employee Stock Purchase Plan [Member]
Shares used in computation:
Weighted-average diluted common shares									3

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	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted weighted average shares outstanding	928	5,528	5,180
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	928	5,468	5,118
Unvested Restricted Stock Units Outstanding [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted weighted average shares outstanding		40	40
Employee Stock Purchase Plan [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted weighted average shares outstanding		20	22

Supplemental Disclosures - Sche

Supplemental Disclosures - Schedules of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Payables And Accruals [Abstract]
Accrued personnel costs	$ 9,484	$ 5,789
Accrued external research and development expenses	4,274	2,072
Accrued licensing costs	1,617
Accrued external general and administrative expenses	773	1,078
Accrued income taxes payable	726
Accrued purchases of property and equipment	221	430
Other accrued expenses and current liabilities	69	236
Accrued expenses and other current liabilities	$ 17,164	$ 9,605

Supplemental Disclosures - Addi

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

Selected Quarterly Financial _3

Selected Quarterly Financial Information (Unaudited) - Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 40,777	$ 5,306	$ 40,031	$ 132,391	$ 2,040	$ 1,336	$ 6,562	$ 455	$ 218,505	$ 10,393	$ 4,589
Total costs of revenues	2,843	517	3,872	2,408	(382)	683	1,317	91
Research and development expense	24,329	18,508	21,486	19,550	14,170	12,518	13,917	16,619	83,873	57,224	45,482
General and administrative expense	11,144	9,008	8,318	8,380	4,808	9,444	6,355	6,622	36,850	27,229	23,590
Total operating expenses	38,327	28,031	33,681	30,366	18,638	22,645	21,618	23,377	130,405	86,278	69,929
Net income (loss)	$ 4,306	$ (19,202)	$ 10,594	$ 104,239	$ (15,997)	$ (20,706)	$ (14,473)	$ (21,993)	$ 99,937	$ (73,169)	$ (62,967)
Basic net income (loss) per share	$ 0.12	$ (0.56)	$ 0.33	$ 3.30	$ (0.51)	$ (0.67)	$ (0.47)	$ (0.82)	$ 2.99	$ (2.45)	$ (2.38)
Diluted net income (loss) per share	$ 0.11	$ (0.56)	$ 0.30	$ 3.04	$ (0.51)	$ (0.67)	$ (0.47)	$ (0.82)	$ 2.73	$ (2.45)	$ (2.38)