0001564590-19-030100 | 10-Q | XBRL Viewer

June 30, 2019

Weighted-average remaining lease term (years)

Weighted-average discount rate

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	Jun. 30, 2019	Dec. 31, 2018
Schedule Of Available For Sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 19,176
Less than 12 Months, Unrealized Losses	(3)	$ (391)
12 Months or Greater, Unrealized Losses		(23)
Total, Fair Value	19,176
Total, Unrealized Losses	(3)	(414)
Less than 12 Months, Fair Value		298,407
12 Months or Greater, Fair Value		12,424
Total, Fair Value		310,831
Corporate Bonds [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than 12 Months, Fair Value	19,176
Less than 12 Months, Unrealized Losses	(3)	(354)
12 Months or Greater, Unrealized Losses		(23)
Total, Fair Value	19,176
Total, Unrealized Losses	$ (3)	(377)
Less than 12 Months, Fair Value		245,283
12 Months or Greater, Fair Value		12,424
Total, Fair Value		257,707
U.S. Government and Federal Agency Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than 12 Months, Unrealized Losses		(37)
Total, Unrealized Losses		(37)
Less than 12 Months, Fair Value		53,124
Total, Fair Value		$ 53,124

Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Current assets
Cash and cash equivalents	$ 55,142	$ 75,561
Marketable securities	286,354	244,200
Accounts receivable	9,679	8,587
Prepaid expenses	6,036	5,734
Other current assets	2,281	3,831
Total current assets	359,492	337,913
Marketable securities	108,194	150,819
Accounts receivable	23,955	23,012
Property and equipment, net	27,330	28,702
Operating lease right-of-use assets	5,904
Restricted cash	1,053	1,053
Other assets	3,211	2,315
Total assets	529,139	543,814
Current liabilities
Accounts payable	5,851	4,412
Accrued expenses and other current liabilities	16,534	17,164
Deferred revenue		600
Operating lease liabilities	2,276
Total current liabilities	24,661	22,176
Deferred revenue	3,333	3,333
Operating lease liabilities	4,654
Deferred rent		1,098
Financing lease obligations		5,854
Other liabilities	1,899	2,505
Total liabilities	34,547	34,966
Commitments and contingencies (Note 7)
Stockholders’ equity
Preferred stock; $0.0001 par value; 10,000 shares authorized, and no shares issued and outstanding at June 30, 2019 and December 31, 2018
Common stock; $0.0001 par value; 100,000 shares authorized at June 30, 2019 and December 31, 2018; 36,752 and 36,120 shares issued and outstanding at June 30, 2019 and December 31, 2018, respectively	4	4
Additional paid-in capital	610,891	592,580
Accumulated other comprehensive income (loss)	471	(720)
Accumulated deficit	(116,774)	(83,016)
Total stockholders’ equity	494,592	508,848
Total liabilities and stockholders’ equity	$ 529,139	$ 543,814

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, 2017	$ 183,029	$ 3	$ 371,497	$ (715)	$ (187,756)
Balances (Shares) at Dec. 31, 2017		31,295
Exercise of stock options	6,999		6,999
Exercise of stock options, Shares		961
Issuance of common stock under employee stock purchase plan	342		342
Issuance of common stock under employee stock purchase plan, shares		20
Stock-based compensation expense	7,272		7,272
Unrealized gain (loss) on available-for-sale securities, net of reclassifications and income tax expense	(56)			(56)
Net income (loss)	114,833				114,833
Balances at Jun. 30, 2018	317,222	$ 3	386,110	(771)	(68,120)
Balances (Shares) at Jun. 30, 2018		32,275
Adoption of ASU \| ASU 2014-09 [Member]	4,803				4,803
Balances at Mar. 31, 2018	299,340	$ 3	378,954	(903)	(78,714)
Balances (Shares) at Mar. 31, 2018		31,900
Exercise of stock options	3,174		3,174
Exercise of stock options, Shares		375
Stock-based compensation expense	3,982		3,982
Unrealized gain (loss) on available-for-sale securities, net of reclassifications and income tax expense	132			132
Net income (loss)	10,594				10,594
Balances at Jun. 30, 2018	317,222	$ 3	386,110	(771)	(68,120)
Balances (Shares) at Jun. 30, 2018		32,275
Balances at Dec. 31, 2018	508,848	$ 4	592,580	(720)	(83,016)
Balances (Shares) at Dec. 31, 2018		36,120
Exercise of stock options	5,129		5,129
Exercise of stock options, Shares		622
Issuance of common stock under employee stock purchase plan	365		365
Issuance of common stock under employee stock purchase plan, shares		10
Stock-based compensation expense	12,817		12,817
Unrealized gain (loss) on available-for-sale securities, net of reclassifications and income tax expense	1,151			1,151
Net income (loss)	(33,685)				(33,685)
Balances at Jun. 30, 2019	494,592	$ 4	610,891	471	(116,774)
Balances (Shares) at Jun. 30, 2019		36,752
Adoption of ASU \| ASU 2016-02 [Member]	(33)				(33)
Adoption of ASU \| ASU 2018-02 [Member]				40	(40)
Balances at Mar. 31, 2019	487,053	$ 4	602,425	(59)	(115,317)
Balances (Shares) at Mar. 31, 2019		36,611
Exercise of stock options	1,367		1,367
Exercise of stock options, Shares		141
Stock-based compensation expense	7,099		7,099
Unrealized gain (loss) on available-for-sale securities, net of reclassifications and income tax expense	530			530
Net income (loss)	(1,457)				(1,457)
Balances at Jun. 30, 2019	$ 494,592	$ 4	$ 610,891	$ 471	$ (116,774)
Balances (Shares) at Jun. 30, 2019		36,752

Summary of Significant Accounting Policies

6 Months Ended

Jun. 30, 2019

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Basis of Presentation and Principles of Consolidation

The accompanying consolidated financial statements are unaudited and have been prepared in conformity with accounting principles generally accepted in the United States of America (GAAP). The interim unaudited consolidated financial statements have been prepared on the same basis as the annual audited consolidated financial statements as of and for the year ended December 31, 2018 included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018, which was filed with the SEC on February 27, 2019. Certain information and footnote disclosures required by GAAP which are normally included in the Company’s annual consolidated financial statements have been omitted pursuant to SEC rules and regulations for interim reporting. In the opinion of management, the accompanying consolidated financial statements reflect all adjustments, which are normal and recurring in nature, necessary for fair financial statement presentation.

The results of operations for the interim periods are not necessarily indicative of the results of operations to be expected for the full year, any other interim periods, or any future year or period. These interim consolidated financial statements should be read in conjunction with the audited consolidated financial statements as of and for the year ended December 31, 2018, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018.

The accompanying consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.

Use of Estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts in the financial statements and accompanying notes. Actual results could differ materially from those estimates. Management considers many factors in selecting appropriate financial accounting policies and controls, and in developing the estimates and assumptions that are used in the preparation of these consolidated financial statements. Management must apply significant judgment in this process. In addition, other factors may affect estimates, including: expected business and operational changes, sensitivity and volatility associated with the assumptions used in developing estimates and whether historical trends are expected to be representative of future trends. The estimation process often may yield a range of potentially reasonable estimates of the ultimate future outcomes and management must select an amount that falls within that range of reasonable estimates. This process may result in actual results differing materially from those estimated amounts used in the preparation of the consolidated financial statements. Significant estimates are used in the following areas, among others: license and royalty revenue, stock-based compensation expense, accrued research and development expenses and other accrued liabilities, income taxes and the fair value of financial instruments.

Reclassifications

Certain amounts reported in prior periods have been reclassified to conform to current period financial statement presentation. These reclassifications are not material and have no effect on previously reported financial position, results of operations and cash flows.

Restricted Cash

Restricted cash includes money market mutual funds used to collateralize irrevocable letters of credit as required by the Company’s lease agreements. The following table provides a reconciliation of cash and cash equivalents and restricted cash as reported on the consolidated balance sheets to the total of these amounts as reported at the end of the period in the consolidated statements of cash flows (in thousands):

	June 30, 2019		June 30, 2018
Cash and cash equivalents	$	55,142	$	106,889
Restricted cash		1,053		225
Total cash and cash equivalents and restricted cash	$	56,195	$	107,114

Marketable Securities

Marketable securities consist of available-for-sale debt securities and equity securities and are carried at fair value. Marketable debt securities with remaining maturity dates exceeding 12 months which are not intended to be sold prior to maturity for use in current operations are classified as non-current assets. Marketable equity securities are classified as current assets.

Unrealized gains and losses on available-for-sale debt securities, net of any related tax effects, are excluded from results of operations and are included in other comprehensive income (loss) and reported as a separate component of stockholders’ equity until realized. The Company uses the aggregate portfolio approach to release the tax effects of unrealized gains and losses on available-for-sale debt securities in accumulated other comprehensive income (loss). Purchase premiums and discounts on marketable debt securities are amortized or accreted into the cost basis over the life of the related security as adjustments to the yield using the effective-interest method. Interest income is recognized when earned. Unrealized gains and losses on marketable equity securities are included in results of operations as investment income. Realized gains and losses from the sale or maturity of marketable securities are based on the specific identification method and are included in results of operations as investment income.

A decline in the fair value below cost of available-for-sale debt securities that is deemed other-than-temporary is charged to results of operations, resulting in the establishment of a new cost basis for the security. The Company regularly evaluates whether declines in the fair value of its debt securities below their cost are other-than-temporary. The evaluation includes consideration of the cause of the impairment, including the creditworthiness of the security issuers, the number of securities in an unrealized loss position, the severity and duration of the unrealized losses, whether the Company has the intent to sell the securities and whether it is more likely than not that the Company will be required to sell the securities before the recovery of their amortized cost basis. The Company has not recorded any impairment of available-for-sale debt securities which was deemed to be to be other-than-temporary.

Leases

Effective January 1, 2019, the Company adopted Accounting Standards Update (ASU) 2016-02, Leases (Topic 842) which supersedes the lease accounting requirements in Accounting Standards Codification (ASC) 840, Leases (Topic 840). Please refer to Recent Accounting Pronouncements below for additional information on the adoption of Topic 842 and the impact upon adoption to the Company’s consolidated financial statements.

Under Topic 842, the Company classifies its leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase by the Company. Lease classification is evaluated at the inception of the lease agreement. Regardless of classification, the Company records a right-of-use asset and a lease liability for all leases with a term greater than 12 months. All of the Company’s leases as of June 30, 2019 have been classified as operating leases. Operating lease expense is recognized on a straight-line basis over the term of the lease, with the exception of variable lease expenses which are recognized as incurred.

The Company identifies leases in its contracts if the contract conveys the right to control the use of identified property, plant or equipment for a period of time in exchange for consideration. The Company does not allocate lease consideration between lease and nonlease components and records a lease liability equal to the present value of the remaining fixed consideration under the lease. The interest rates implicit in the Company’s leases are generally not readily determinable. Accordingly, the Company uses its estimated incremental borrowing rate at the commencement date of the lease to determine the present value discount of the lease liability. The Company estimates its incremental borrowing rate for each lease based on an evaluation of its expected credit rating and the prevailing market rates for collateralized debt in a similar economic environment with similar payment terms and maturity dates commensurate with the term of the lease. The right-of-use asset for each lease is equal to the lease liability, adjusted for unamortized initial direct costs and lease incentives and prepaid or accrued rent. Initial direct costs of entering into a lease are included in the right-of-use asset and amortized as lease expense over the term of the lease. Lease incentives, such as tenant improvements allowances, are recorded as a reduction of the right-of-use asset and amortized as a reduction of lease expense over the term of the lease. The Company excludes options to extend or terminate leases from the calculation of the lease liability unless it is reasonably certain the option will be exercised.

Fair Value of Financial Instruments

The Company is required to disclose information on all assets and liabilities reported at fair value that enables an assessment of the inputs used in determining the reported fair values. ASC 820, Fair Value Measurements and Disclosures, establishes a hierarchy of inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that the observable inputs be used when available. Observable inputs are inputs that market participants would use in pricing the asset or liability based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the inputs that market participants would use in pricing the asset or liability, and are developed based on the best information available in the circumstances. The fair value hierarchy applies only to the valuation inputs used in determining the reported fair value of the investments and is not a measure of the investment credit quality. The three levels of the fair value hierarchy are described below:

•

Level 1—Valuations based on unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date.

•

Level 2—Valuations based on quoted prices for similar assets or liabilities in markets that are not active or for which all significant inputs are observable, either directly or indirectly.

•

Level 3—Valuations that require inputs that reflect the Company’s own assumptions that are both significant to the fair value measurement and unobservable.

To the extent that valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. The fair values of the Company’s Level 2 instruments are based on quoted market prices or broker or dealer quotations for similar assets. These investments are initially valued at the transaction price and subsequently valued utilizing third party pricing providers or other market observable data. Please refer to Note 4 for further information on the fair value measurement of the Company’s financial instruments.

Revenue Recognition

The Company recognizes revenue in accordance with ASC 606, Revenue from Contracts with Customers (Topic 606). 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 with customers for the presence of significant financing components. If a significant financing component is identified in a contract and provides a financing benefit to the customer, the transaction price for the contract is adjusted to account for the financing portion of the arrangement, which is recognized as interest income over the financing term using the effective interest method. In determining the appropriate interest rates for significant financing components, the Company evaluates the credit profile of the customer and prevailing market interest rates and selects an interest rate in which it believes would be charged to the customer in a separate financing arrangement over a similar financing term.

License and Royalty Revenue

The Company licenses its NAV Technology Platform to other biotechnology and pharmaceutical companies. The terms of the licenses vary, and licenses may be exclusive or non-exclusive and may be sublicensable by the licensee. Licenses may grant intellectual property rights for purposes of internal and preclinical research and development only, or may include the rights, or options to obtain future rights, to commercialize drug therapies for specific diseases using the Company’s NAV Technology Platform. License agreements generally have a term at least equal to the life of the underlying patents, but are terminable at the option of the licensee. Consideration payable to the Company under its license agreements may include: (i) up-front and annual fees, (ii) option fees to acquire additional licenses, (iii) milestone payments based on the achievement of certain development and sales-based milestones by licensees, (iv) sublicense fees and (v) royalties on sales of licensed products.

The Company’s license agreements are accounted for as contracts with customers within the scope of Topic 606. At the inception of each license agreement, the Company determines the contract term for purposes of applying the requirements of Topic 606. Licenses are generally terminable at the option of the licensee with advance notice to the Company. For each license, the Company evaluates these termination rights to determine whether a substantive termination penalty would be incurred by the licensee upon termination. If the licensee incurs a substantive termination penalty upon termination, the contract term for revenue recognition purposes is generally equal to the stated term of the license, which is the life of the underlying licensed patents. Alternatively, if the licensee does not incur a substantive termination penalty upon termination, the contract term for revenue recognition purposes may be shorter than the stated term of the license, in which case the termination rights may be accounted for as contract renewal options. The determination of whether a substantive termination penalty is associated with the termination rights requires significant judgment. In making this determination, the Company considers, among other things, the nature of the intellectual property rights that would be returned to the Company upon termination, including the exclusivity of the licensed rights and the stage of development of the licensed products, the payment terms, including the amount and timing of non-refundable or guaranteed payments, and the business purpose of the termination rights granted to the licensee. The Company considers all of the facts and circumstances relevant to each license when making this determination.

Performance obligations under the Company’s license agreements may include (i) the delivery of intellectual property licenses and (ii) options granted to licensees to acquire additional licenses to the extent the options represent material rights to the licensee. At the inception of each license agreement which contains options for the licensee to acquire additional licenses, or contract renewal options, the Company evaluates the options to determine whether they provide material rights to the licensee. In making this determination, the Company considers whether the options are priced at a discount to the standalone selling price for the underlying licenses. If an option is priced at a discount to the standalone selling price for the underlying license, the option is considered to be a material right to the licensee and is accounted for as a separate performance obligation under the current license agreement.

The Company evaluates the transaction price of its license agreements at the inception of each agreement and at each reporting date. The transaction price includes the fixed consideration payable to the Company during the contract term, as well as any variable consideration to the extent that it is probable that a significant reversal of revenue will not occur in the future. Fixed consideration under the license agreements includes up-front and annual fees payable during the contract term. Variable consideration under the license agreements includes development and sales-based milestone payments, sublicense fees and royalties on sales of licensed products. Consideration contingent upon the exercise of options by a licensee is excluded from the transaction price and not accounted for as part of the license agreement until the option is exercised.

The transaction price for each license agreement is allocated to the underlying performance obligations and recognized as revenue when the performance obligations are satisfied. Consideration allocated to performance obligations for the delivery of an intellectual property license is recognized as revenue in full upon the delivery of the license to the licensee. Consideration allocated to performance obligations for license options is recognized as revenue in full upon the earlier of the option exercise or expiration. The exercise of a license option by a licensee is accounted for as a new license for revenue recognition purposes.

Up-front and annual licenses fees payable to the Company over the contract term of each license are included in the transaction price, and the portion of this consideration that is allocated to the performance obligation for the delivery of the intellectual property license is recognized as revenue in full upon the delivery of the license to the licensee. If annual license fees are payable to the Company in periods beyond 12 months from the delivery of the license, a significant financing component is deemed to exist which provides a financing benefit to the licensee. If a significant financing component is identified, the Company adjusts the transaction price for the license to include only the present value of the annual license fees payable to the Company over the contract term. The discounted portion of the license fees is recognized as interest income from licensing over the financing period of the license.

Development milestone payments are payable to the Company upon the achievement of specified development milestones by licensees. At the inception of each license agreement that contains development milestone payments, the Company evaluates whether the milestones are considered probable of achievement and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal will not occur in the future, milestone payments are included in the transaction price and recognized as revenue upon the delivery of the license. Milestone payments contingent on the achievement of development milestones that are not within the control of the Company or the licensee, such as regulatory approvals, are not considered probable of being achieved and are excluded from the transaction price until the milestone is achieved. At each reporting date, the Company re-evaluates the probability of achievement of outstanding development milestones and, if necessary, adjusts the transaction price for any milestones for which the probability of achievement has changed due to current facts and circumstances. Any such adjustments are recorded on a cumulative catch-up basis and recognized as revenue in the period of the adjustment.

Royalties on sales of licensed products, sales-based milestone payments and sublicense fees based on the receipt of certain fees by licensees from any sublicensees are excluded from the transaction price of each license and recognized as revenue in the period that the related sales or sublicenses occur, provided that the associated license has been delivered to the licensee.

Royalty revenue to date consists of royalties on net sales of Zolgensma®, which is marketed by AveXis, Inc. (AveXis), a wholly owned subsidiary of Novartis AG (Novartis). Zolgensma is a licensed product under the Company’s March 2014 license agreement, as amended, with AveXis for the development and commercialization of treatments for spinal muscular atrophy (SMA). The Company recognizes royalty revenue from net sales of Zolgensma in the period in which the underlying products are sold by AveXis, which in certain cases may require the Company to estimate royalty revenue for periods of net sales which have not yet been reported to the Company. Sales-based milestone payments related to net sales of Zolgensma are recognized as royalty revenue in the period in which the milestone is achieved.

The Company receives payments from licensees based on the billing schedules established in each license agreement. Amounts recognized as revenue which have not yet been received from licensees, including unbilled royalties, are recorded as accounts receivable when the Company’s rights to the consideration are conditional solely upon the passage of time. Amounts recognized as revenue which have not yet been received from licensees are recorded as contract assets when the Company’s rights to the consideration are not unconditional. Contract assets are recorded as other current assets on the consolidated balance sheets. If a licensee elects to terminate a license prior to the end of the license term, the licensed intellectual property is returned to the Company and any consideration recorded as accounts receivable or contract assets which is not contractually payable by the licensee is charged off as a reduction of license revenue in the period of the termination. Amounts received by the Company prior to the delivery of underlying performance obligations are deferred and recognized as revenue upon the satisfaction of the performance obligations by the Company. Deferred revenue which is not expected to be recognized within 12 months from the reporting date is recorded as non-current on the consolidated balance sheets.

Cost of Revenues

Cost of revenues consists primarily of sublicense fees, milestone payments and royalties on net sales of licensed products as specified in the Company’s agreements with its licensors. Sublicense fees are based on a percentage of license fees received by the Company from NAV Technology Licensees and are recognized in the period that the underlying license revenue is recognized. Milestone payments are payable to licensors upon the achievement of specified milestones by NAV Technology Licensees and are recognized in the period the milestone is achieved or deemed probable of achievement. Royalties are based on a percentage of net sales of licensed products by NAV Technology Licensees and are recognized in the period that the underlying sales occur. Amounts which are payable to licensors in periods beyond 12 months from the reporting date are recorded as non-current liabilities on the consolidated balance sheets.

Net Income (Loss) Per Share

Basic net income (loss) per share is calculated by dividing net income (loss) applicable to common stockholders by the weighted-average common shares outstanding during the period, without consideration for common stock equivalents. Diluted net income (loss) per share is calculated by adjusting the weighted-average common shares outstanding for the dilutive effect of common stock equivalents outstanding for the period, determined using the treasury-stock method. Contingently convertible shares in which conversion is based on non-market-priced contingencies are excluded from the calculations of both basic and diluted net income (loss) per share until the contingency has been fully met. For purposes of the diluted net income (loss) per share calculation, common stock equivalents are excluded from the calculation of diluted net income (loss) per share if their effect would be anti-dilutive.

Recent Accounting Pronouncements

Adoption of ASU 2016-02, Leases

In February 2016, the Financial Accounting Standards Board (FASB) issued ASU 2016-02, Leases (Topic 842) which supersedes the lease accounting requirements in ASC 840, Leases (Topic 840). Effective January 1, 2019, the Company adopted Topic 842 using the modified retrospective transition method. Under this method, the Company applied Topic 842 to all leases in effect as of, or entered into after, January 1, 2019 and recorded the cumulative impact of the adoption as an adjustment to its accumulated deficit on January 1, 2019. The Company’s consolidated financial statements for periods ending after January 1, 2019 are presented in accordance with the requirements of Topic 842, while comparative prior period amounts have not been adjusted and continue to be reported in accordance with Topic 840. Please refer to Leases above for a description of the Company’s lease accounting policies upon the adoption on Topic 842.

The Company elected certain practical expedients allowed by Topic 842 for transition purposes, including the package of practical expedients which permitted the Company to not reassess lease identification, classification and initial direct costs under Topic 842 for leases that commenced prior to January 1, 2019. Additionally, the Company elected the practical expedient allowed for transition purposes to use hindsight in determining the terms of leases that commenced prior to January 1, 2019.

Upon the adoption of Topic 842, the Company recorded operating lease right-of-use assets of $7.4 million and operating lease liabilities of $8.4 million for its leases which were in effect and had commenced prior to January 1, 2019 and had original lease terms of more than 12 months. The Company also derecognized current and non-current deferred rent liabilities of $1.4 million and prepaid expenses, other current assets and other assets of $0.4 million upon the adoption of Topic 842. Additionally, upon the adoption of Topic 842, the Company derecognized $5.9 million of property and equipment and $5.9 million of financing lease obligations related to construction-in-progress at 9800 Medical Center Drive, as the Company does not control the building during the construction period under the requirements of Topic 842. The lease term for the facility at 9800 Medical Center Drive does not commence until certain construction is completed by the landlord and the building is delivered to the Company. The right-of-use assets and lease liabilities related to the facility at 9800 Medical Center Drive will not be recognized on the Company’s consolidated balance sheets until the commencement date of the lease, which is expected to occur in 2020.

The cumulative impact of the adoption of Topic 842 resulted in an increase in accumulated deficit of less than $0.1 million on January 1, 2019. The adoption of Topic 842 did not have a material impact on the Company’s results of operations for the three and six months ended June 30, 2019, nor does the Company believe it will have a material impact on future results of operations based on its current leasing arrangements.

Other Recently Adopted Accounting Pronouncements

In 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, which amends the current guidance on comprehensive income to provide an option for an entity to reclassify the stranded tax effects of the Tax Cuts and Jobs Act of 2017 (the TCJA) that was signed into law in December 2017 from accumulated other comprehensive income directly to retained earnings. The stranded tax effects result from the remeasurement of deferred tax assets and liabilities which were originally recorded in comprehensive income but whose remeasurement is reflected in the income statement. The Company adopted this standard effective January 1, 2019, and upon adoption recorded a cumulative adjustment of less than $0.1 million to reclassify the stranded tax effects of unrealized gains and losses on available-for-sale securities from accumulated other comprehensive income (loss) to accumulated deficit. The adoption of this standard did not have a material impact on the Company’s financial position or results of operations.

In April 2017, the FASB issued ASU 2017-08, Receivables—Nonrefundable Fees and Other Costs (Subtopic 310-20), which amends the required amortization period for certain purchased callable debt securities held at a premium by shortening the amortization period for the premium to the earliest call date. The Company adopted this standard effective January 1, 2019. The adoption of this standard required no cumulative-effect adjustments and did not have a material impact on the Company’s financial position or results of operations.

Recent Accounting Pronouncements Not Yet Adopted

In August 2018, the FASB issued ASU 2018-15, Intangibles—Goodwill and Other—Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract. The standard aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangements that include an internal-use software license). The standard is effective for the Company beginning January 1, 2020, with early adoption permitted upon issuance, and may be applied either retrospectively or prospectively to all implementation costs incurred after the date of adoption. The Company is evaluating the application of this standard but has not yet determined the potential effects it may have on its consolidated financial statements.

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, which modifies certain disclosure requirements regarding fair value measurements. The standard is effective for the Company beginning January 1, 2020, with early adoption permitted upon issuance. The Company does not believe the application of this standard will have a material impact on its financial statement disclosures.

In June 2016, the FASB issued ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, which amends the accounting for credit losses for most financial assets and certain other instruments. The standard requires that entities holding financial assets that are not accounted for at fair value through net income be presented at the net amount expected to be collected. An allowance for credit losses will be a valuation account that will be deducted from the amortized cost basis of the financial asset to present the net carrying value at the amount expected to be collected on the financial asset. The standard is effective for the Company beginning January 1, 2020, with early adoption permitted for annual and interim periods beginning January 1, 2019. The Company does not believe the application of this standard will have a material impact on its financial position or results of operations.

Stock-based Compensation

6 Months Ended

Jun. 30, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-based Compensation

9. Stock-based Compensation

In January 2019, an additional 1,444,808 shares became available for issuance under the 2015 Equity Incentive Plan (the 2015 Plan). As of June 30, 2019, the total number of shares of common stock authorized for issuance under the 2015 Plan and the 2014 Stock Plan (the 2014 Plan) was 10,933,221, of which 2,327,843 remained available for future grants under the 2015 Plan.

Stock-based Compensation Expense

The Company’s stock-based compensation expense by award type was as follows (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Stock options	$	6,844	$	3,818	$	12,296	$	6,939
Restricted stock units		69		69		136		136
Employee stock purchase plan		186		95		385		197
	$	7,099	$	3,982	$	12,817	$	7,272

As of June 30, 2019, the Company had $70.4 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 3.0 years.

The Company has recorded aggregate stock-based compensation expense in the consolidated statements of operations and comprehensive income (loss) as follows (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Research and development	$	3,526	$	1,895	$	5,873	$	3,424
General and administrative		3,573		2,087		6,944		3,848
	$	7,099	$	3,982	$	12,817	$	7,272

Stock Options

The following table summarizes stock option activity under the 2014 Plan and 2015 Plan (in thousands, except per share data):

						Weighted-
						average
				Weighted-		Remaining
				average		Contractual		Aggregate
				Exercise		Life		Intrinsic
	Shares			Price		(Years)		Value (a)
Outstanding at December 31, 2018		4,855		$	19.31		7.6	$	118,185
Granted		1,410		$	48.48
Exercised		(621	)	$	8.24
Cancelled or forfeited		(190	)	$	32.92
Outstanding at June 30, 2019		5,454		$	27.64		7.8	$	136,336
Exercisable at June 30, 2019		2,630		$	13.65		6.7	$	99,341
Vested and expected to vest at June 30, 2019		5,454		$	27.64		7.8	$	136,336

(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 six months ended June 30, 2019 was $32.24. During the six months ended June 30, 2019, the total number of stock options exercised was 621,415, resulting in total proceeds of $5.1 million. The total intrinsic value of options exercised during the six months ended June 30, 2019 was $25.5 million.

Restricted Stock Units

The following table summarizes restricted stock unit activity under the 2015 Plan (in thousands, except per share data):

			Weighted-
			average
			Grant Date
	Shares		Fair Value
Unvested balance at December 31, 2018		40	$	20.90
Granted		—	$	—
Vested		—	$	—
Forfeited		—	$	—
Unvested balance at June 30, 2019		40	$	20.90

Employee Stock Purchase Plan

As of June 30, 2019, the total number of shares of common stock authorized for issuance under the 2015 ESPP was 254,000, of which 159,339 remained available for future issuance. During the six months ended June 30, 2019, 10,241 shares of common stock were issued under the 2015 ESPP.

Fair Value of Financial Instruments (Tables)

6 Months Ended

Jun. 30, 2019

Fair Value Disclosures [Abstract]

Schedule of Fair Value of Cash Equivalents and Marketable Securities

The following tables present the fair value of cash equivalents and marketable securities in accordance with the hierarchy discussed in Note 2 (in thousands):

	Quoted		Significant
	prices		other		Significant
	in active		observable		unobservable
	markets		inputs		inputs
	(Level 1)		(Level 2)		(Level 3)		Total
June 30, 2019
Cash equivalents:
Money market mutual funds	$	—	$	55,126	$	—	$	55,126
Total cash equivalents		—		55,126		—		55,126
Marketable securities:
U.S. government and federal agency securities		—		103,213		—		103,213
Certificates of deposit		—		8,815		—		8,815
Corporate bonds		—		250,444		—		250,444
Equity securities		32,076		—		—		32,076
Total marketable securities		32,076		362,472		—		394,548
Total cash equivalents and marketable securities	$	32,076	$	417,598	$	—	$	449,674

	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

License and Royalty Revenue - Additional Information (Detail)	1 Months Ended			3 Months Ended		6 Months Ended
	May 31, 2018 USD ($)	Jan. 31, 2018 USD ($)	Mar. 31, 2014 USD ($)	Jun. 30, 2019 USD ($) ProductCandidate TechnologyLicensee	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) ProductCandidate TechnologyLicensee	Jun. 30, 2018 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
License Revenue [Line Items]
Milestone payment upon commencement of clinical trials in humans						$ 18,600,000
Milestone payment upon submission of regulatory approval filings						32,500,000
Milestone payment upon approval of commercial products by regulatory agencies						81,000,000.0
Milestone payment upon achievement of specified sales targets for licensed products						187,000,000.0
Accounts receivable				$ 33,634,000	$ 5,224,000	33,634,000	$ 5,224,000	$ 31,130,000	$ 31,599,000	$ 58,621,000	$ 5,850,000
Deferred revenue, current and non-current				3,333,000	600,000	3,333,000	600,000	3,933,000	3,933,000
Licenses revenue				7,881,000	40,031,000	8,765,000	172,422,000
Impirment losses on receivables or contract assets						0
Billed to customers				200,000		200,000			400,000
Billable to customers in future periods				33,400,000		33,400,000			31,200,000
Allowance for doubtful accounts				0		$ 0			0
Transaction price description						Upon its execution, the transaction price of the January 2018 Amendment was $132.1 million, which was fully recognized as license revenue upon the delivery of the modified license in January 2018. In May 2018, as a result of the acquisition of AveXis by Novartis, the transaction price was increased by $40.0 million to account for the acceleration of the sale-based milestone which was previously excluded from the transaction price. The $40.0 million increase in the transaction price was recognized as license revenue upon the completion of the change of control in May 2018 since the amended license had been fully delivered to AveXis. Additionally, due to the acceleration of the two $30.0 million payments originally due in January 2019 and January 2020, the Company recognized $6.1 million of interest income from licensing upon the completion of the change of control of AveXis, which represents the remaining present value discount on such payments as of the date of the change of control. As of June 30, 2019, the transaction price of the January 2018 Amendment was $172.1 million, which includes: (i) the $80.0 million payment in January 2018, (ii) the present value, as of the date of the January 2018 Amendment, of the two $30.0 million payments originally due in January 2019 and January 2020 and (iii) the $40.0 million sales-based milestone which was accelerated upon the change of control in May 2018. Variable consideration under the January 2018 Amendment, which has been excluded from the transaction price, includes the remaining sales-based milestone payment of $80.0 million, as well as any potential sublicense fees or royalties on sales of licensed products, which will be recognized in the period of the underlying sales or sublicenses.
Interest income from licensing				762,000	6,898,000	$ 1,375,000	8,253,000
Accounts receivable, current				9,679,000		9,679,000			8,587,000
AveXis, Inc. [Member]
License Revenue [Line Items]
Interest income from licensing				7,000	6,752,000	15,000	7,950,000
License [Member]
License Revenue [Line Items]
Licenses revenue				600,000	0	600,000
License [Member] \| AveXis, Inc. [Member]
License Revenue [Line Items]
Licenses revenue				$ 4,424,000	40,000,000	$ 4,424,000	172,066,000
NAV Technology Licensees [Member] \| NAV Technology Platform [Member]
License Revenue [Line Items]
Number of technology licensees \| TechnologyLicensee				9		9
NAV Technology Licensees [Member] \| NAV Technology Platform [Member] \| Minimum [Member]
License Revenue [Line Items]
Number of development partnered product candidates \| ProductCandidate				20		20
March 2014 Licence Agreement [Member] \| AveXis, Inc. [Member]
License Revenue [Line Items]
License fees received					100,000,000.0
Accounts receivable										$ 53,300,000
Accounts receivable				$ 1,100,000		$ 1,100,000			200,000
Up-front fee paid			$ 2,000,000.0			2,000,000.0
Milestone fee payments upon achievement of various development and commercialization			$ 12,300,000
License agreement amendment date			2018-01
Transaction price of license				11,000,000.0		11,000,000.0
Payments for remaining development milestones				3,500,000		3,500,000
Increase in transaction price of license				3,500,000		3,500,000
Accounts receivable, current				900,000		900,000
Accounts receivable, non -current				200,000		200,000
March 2014 Licence Agreement [Member] \| Maximum [Member] \| AveXis, Inc. [Member]
License Revenue [Line Items]
Accounts receivable, current									100,000
Accounts receivable, non -current									200,000
License Agreement [Member] \| License [Member]
License Revenue [Line Items]
License revenue				3,200,000	$ 39,900,000	4,000,000.0	$ 200,000
Proceeds from milestone license revenue	$ 40,000,000.0
November 2018 License Agreement [Member] \| Abeona Therapeutics Inc. [Member]
License Revenue [Line Items]
Accounts receivable				27,300,000		27,300,000			$ 26,000,000.0
January 2018 Amendment Agreement [Member] \| AveXis, Inc. [Member]
License Revenue [Line Items]
License fees received	100,000,000.0
License agreement period		14 years
License fee		$ 80,000,000.0
Sales-based milestone payment unpaid in the event of change of control		40,000,000.0
Transaction price of license		132,100,000		$ 172,100,000		172,100,000
Increase in transaction price of license						0
Interest income from licensing	6,100,000
Sales-based milestone payment exclude transaction price						$ 80,000,000.0
Payments due from related party								$ 30,000,000.0
Consideration payment due period one						2019-01
Consideration payment due period two						2020-01
January 2018 Amendment Agreement [Member] \| AveXis, Inc. [Member] \| Share-based Milestone [Member]
License Revenue [Line Items]
Increase in transaction price of license	40,000,000.0
January 2018 Amendment Agreement [Member] \| AveXis, Inc. [Member] \| First Anniversary [Member]
License Revenue [Line Items]
License fee		30,000,000.0
January 2018 Amendment Agreement [Member] \| AveXis, Inc. [Member] \| Second Anniversary [Member]
License Revenue [Line Items]
License fee		30,000,000.0
January 2018 Amendment Agreement [Member] \| Minimum [Member] \| AveXis, Inc. [Member]
License Revenue [Line Items]
Milestone payment		$ 120,000,000.0
January 2018 Amendment Agreement [Member] \| License [Member] \| AveXis, Inc. [Member]
License Revenue [Line Items]
Increase in transaction price of license	$ 40,000,000.0

Net Income (Loss) Per Share

6 Months Ended

Jun. 30, 2019

Earnings Per Share [Abstract]

Net Income (Loss) Per Share

12. Net Income (Loss) Per Share

The computations of basic and diluted net income (loss) per share are as follows (in thousands, except per share data):

	Three Months Ended June 30,					Six Months Ended June 30,
	2019			2018		2019			2018
Basic net income (loss) per share:
Net income (loss) applicable to common stockholders	$	(1,457	)	$	10,594	$	(33,685	)	$	114,833
Shares used in computation:
Weighted-average common shares outstanding		36,669			32,082		36,518			31,858
Basic net income (loss) per share	$	(0.04	)	$	0.33	$	(0.92	)	$	3.60
Diluted net income (loss) per share:
Net income (loss) applicable to common stockholders	$	(1,457	)	$	10,594	$	(33,685	)	$	114,833
Shares used in computation:
Weighted-average common shares outstanding		36,669			32,082		36,518			31,858
Stock options		—			3,153		—			2,995
Restricted stock units		—			30		—			27
Employee stock purchase plan		—			7		—			4
Weighted-average diluted common shares		36,669			35,272		36,518			34,884
Diluted net income (loss) per share	$	(0.04	)	$	0.30	$	(0.92	)	$	3.29

For periods in which the Company incurred net losses applicable to common stockholders, common stock equivalents are excluded from the calculation of diluted net loss per share as their effect would be anti-dilutive, and accordingly, basic and diluted net loss per share are the same for such periods. Outstanding stock options with exercise prices greater than the average market price of common stock are excluded from the calculation of diluted net income (loss) per share as their effect would be anti-dilutive. The following potentially dilutive common stock equivalents outstanding at the end of the period were excluded from the computations of weighted-average diluted common shares for the periods indicated as their effects would be anti-dilutive (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Stock options issued and outstanding		5,454		804		5,454		1,236
Unvested restricted stock units outstanding		40		—		40		—
Employee stock purchase plan		26		—		26		—
		5,520		804		5,520		1,236

License and Royalty Revenue

6 Months Ended

Jun. 30, 2019

License Agreement Revenue Recognition [Abstract]

License and Royalty Revenue

8. License and Royalty Revenue

As of June 30, 2019, the Company’s NAV Technology Platform was being applied in the development of more than 20 partnered product candidates by nine NAV Technology Licensees. Consideration to the Company under its license agreements may include: (i) up-front and annual fees, (ii) option fees to acquire additional licenses, (iii) milestone payments based on the achievement of certain development and sales-based milestones by licensees, (iv) sublicense fees and (v) royalties on sales of licensed products. Sublicense fees vary by license and range from a mid-single digit percentage to a low-double digit percentage of license fees received by licensees as a result of sublicenses. Royalties on net sales of commercialized products vary by license and range from a mid-single digit percentage to a low double-digit percentage of net sales by licensees.

Development milestone payments are only included in the transaction price of each license and recognized as 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 June 30, 2019, the Company’s license agreements, excluding additional licenses that could be granted upon the exercise of options by licensees, contained unachieved milestones which could result in aggregate milestone payments to the Company of up to $18.6 million upon the commencement of various stages of clinical trials, $32.5 million upon the submission of regulatory approval filings, $81.0 million upon the approval of commercial products by regulatory agencies and $187.0 million upon the achievement of specified sales targets for licensed products. To the extent the milestone payments are realized by the Company, the Company will be obligated to pay sublicense fees to licensors based on a specified percentage of the fees earned by the Company. The achievement of milestones by licensees is highly dependent on the successful development and commercialization of licensed products and it is at least reasonably possible that some or all of the milestone fees will not be realized by the Company.

The following tables present changes in the balances of the Company’s receivables, contract assets and contract liabilities during the periods presented (in thousands):

	Balance at
	Beginning		Net Additions			Balance at
	of Period		(Deductions)			End of Period
Three Months Ended June 30, 2019
Receivables and contract assets:
Accounts receivable, current and non-current	$	31,130	$	2,504		$	33,634
Contract assets	$	1,000	$	(1,000	)	$	—
Contract liabilities:
Deferred revenue, current and non-current	$	3,933	$	(600	)	$	3,333

	Balance at
	Beginning		Net Additions			Balance at
	of Period		(Deductions)			End of Period
Six Months Ended June 30, 2019
Receivables and contract assets:
Accounts receivable, current and non-current	$	31,599	$	2,035		$	33,634
Contract assets	$	750	$	(750	)	$	—
Contract liabilities:
Deferred revenue, current and non-current	$	3,933	$	(600	)	$	3,333

	Balance at
	Beginning		Net Additions			Balance at
	of Period		(Deductions)			End of Period
Three Months Ended June 30, 2018
Receivables and contract assets:
Accounts receivable, current and non-current	$	58,621	$	(53,397	)	$	5,224
Contract assets	$	250	$	(250	)	$	—
Contract liabilities:
Deferred revenue, current and non-current	$	—	$	600		$	600

	Balance at
	Beginning		Net Additions			Balance at
	of Period		(Deductions)			End of Period
Six Months Ended June 30, 2018
Receivables and contract assets:
Accounts receivable, current and non-current	$	5,850	$	(626	)	$	5,224
Contract assets	$	350	$	(350	)	$	—
Contract liabilities:
Deferred revenue, current and non-current	$	—	$	600		$	600

The net increases in accounts receivable during the three and six months ended June 30, 2019 were primarily attributable to additional licenses granted by the Company during the periods as a result of license options exercised by licensees. The net decrease in accounts receivable during the three months ended June 30, 2018 was primarily attributable to the acceleration and collection of $100.0 million in license fees under our amended March 2014 license agreement with AveXis as a result of their acquisition by Novartis in May 2018. Of the $100.0 million received, $53.3 million was previously recorded as accounts receivable at the beginning of the period.

As of June 30, 2019, the Company had recorded deferred revenue, current and non-current, of $3.3 million which represents consideration received from licensees for performance obligations that have not yet been satisfied by the Company. Unsatisfied performance obligations consist of options granted to licensees that provide material rights to the licensee to acquire additional licenses from the Company. These performance obligations will be satisfied, and underlying revenue will be recognized, upon the exercise or expiration of the options. During the three and six months ended June 30, 2019, the Company recognized $0.6 million of license revenue that was previously included in deferred revenue at the beginning of the period as a result of options exercised by licensees during the period. The Company did not recognize any license revenue during the three and six months ended June 30, 2018 that was included in deferred revenue at the beginning of the period.

During the three and six months ended June 30, 2019, the Company recognized license revenue of $3.2 million and $4.0 million, respectively, from licenses delivered to licensees in prior periods as a result of changes in the transaction prices of its license agreements. Changes in the transaction prices during the three and six months ended June 30, 2019 were primarily attributable to development milestones achieved or deemed probable of achievement during the period that were previously not considered probable of achievement. During the three and six months ended June 30, 2018, the Company recognized license revenue of $39.9 million and $0.2 million, respectively, from licenses delivered to licensees in prior periods as a result of changes in the transaction prices of its license agreements. Changes in the transaction prices during the three and six months ended June 30 2018 were primarily attributable to development milestones achieved or deemed probable of achievement during the period that were previously not considered probable of achievement, as well as the acquisition of AveXis by Novartis in May 2018 resulting in the accelerated payment of $40.0 million of sales-based milestones which were previously excluded from the transaction price of the license.

As of June 30, 2019, the Company had recorded total current and non-current accounts receivable of $33.6 million, of which $0.2 million had been billed to customers and $33.4 million was billable to customers in future periods. As of December 31, 2018, the Company had recorded total current and non-current accounts receivable of $31.6 million, of which $0.4 million had been billed to customers and $31.2 million was billable to customers in future periods.

Accounts receivable, current and non-current, as of June 30, 2019 and December 31, 2018 included $27.3 million and $26.0 million, respectively, related to the November 2018 license agreement with Abeona Therapeutics Inc. for the development and commercialization of treatments for various diseases. The Company believes that it is not exposed to significant credit risk related to accounts receivable due to the credit quality and history of collections from its significant customers. The Company is unaware of any concentrations of credit risk related to accounts receivable from significant customers with deteriorated credit quality. As of June 30, 2019 and December 31, 2018, the Company had not recognized any impairment losses on its receivables or contract assets from contracts with customers and no allowance for doubtful accounts was recorded.

AveXis March 2014 License and January 2018 Amendment

In March 2014, the Company entered into an exclusive license agreement (the March 2014 License) with AveXis. Under the license, the Company granted AveXis an exclusive, worldwide commercial license, with rights to sublicense, to the NAV AAV9 vector for the treatment of SMA in humans by in vivo gene therapy. In consideration for the license, AveXis paid the Company an up-front fee of $2.0 million, and is required to pay annual fees, development milestone payments of up to $12.3 million, mid-single to low double-digit royalties on net sales of licensed products, subject to reduction in specified circumstances, and a lower mid-double digit percentage of any sublicense fees AveXis receives from sublicensees for the licensed intellectual property rights.

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, sublicenses to other third-party patents exclusively licensed by the Company as well as any other recombinant AAV vector in the Company’s intellectual property portfolio during a period of 14 years from the effective date of the January 2018 Amendment, for the treatment of SMA in humans by in vivo gene therapy. The Company may also, in its sole discretion, provide specified collaborative services to AveXis as specified in the January 2018 Amendment.

The January 2018 Amendment also modified the assignment provision of the March 2014 License. Under the amended assignment provision, AveXis was permitted to transfer the March 2014 License, as amended, without the Company’s consent in connection with a change of control of AveXis, subject to certain conditions. Under the original March 2014 License, any assignment by AveXis without the Company’s prior written consent had been prohibited.

In consideration for the additional rights granted under the January 2018 Amendment, and in addition to any consideration owed under the original March 2014 License, AveXis paid to the Company a fee of $80.0 million upon entry into the January 2018 Amendment. In addition, AveXis was obligated to pay the Company (i) $30.0 million on the first anniversary of the effective date of the January 2018 Amendment, (ii) $30.0 million on the second anniversary of the effective date of the January 2018 Amendment and (iii) potential sales-based milestone payments of up to $120.0 million. In the event of a change of control of AveXis, to the extent that any fee described in (i) or (ii) above, or the first $40.0 million of sales-based milestone payments described in (iii) above, had not yet been paid to the Company, AveXis was required to pay any such unpaid fee to the Company upon the change of control. For any product developed for the treatment of SMA using the NAV AAV9 vector, AveXis will continue to be obligated to pay to the Company mid-single to low double-digit royalties on net sales as required by the March 2014 License, and for any product developed for the treatment of SMA using a licensed vector other than NAV AAV9, the Company will receive a low double-digit royalty on net sales.

In May 2018, AveXis was acquired by Novartis, which qualified as a change of control of AveXis under the January 2018 Amendment. Pursuant to the January 2018 Amendment, AveXis paid the Company $100.0 million in accelerated license payments as a result of the change of control.

In May 2019, the U.S. Food and Drug Administration (the FDA) approved Zolgensma for marketing in the United States, which is a licensed product under the March 2014 License, as amended, with AveXis. Upon its commercial launch in the second quarter of 2019, the Company began recognizing royalty revenue on net sales of Zolgensma.

Accounting Analysis

The January 2018 Amendment was accounted for under Topic 606 as a modification of the license agreement resulting in a new and separate contract from the original March 2014 License for revenue recognition purposes. The Company determined that a substantive termination penalty is associated with AveXis’ termination rights under the amended license agreement, and therefore the contract term for revenue recognition purposes is equal to the stated term of the license. The only material performance obligation of the Company under the January 2018 Amendment is for the delivery of the modified license, which occurred upon the execution of the amendment in January 2018.

As of June 30, 2019, the transaction price of the original March 2014 License was $11.0 million. The transaction price includes (i) the up-front payment in March 2014 of $2.0 million, (ii) the present value of aggregate annual fees payable to the Company over the term of the license and (iii) payments for development milestones achieved to date or which are deemed probable of achievement. The discounted portion of the annual fees represents the financing benefit provided to AveXis and is recognized as interest income from licensing over the term of the license. Variable consideration under the original March 2014 License, which has been excluded from the transaction price, includes $3.5 million in payments for remaining development milestones that had not yet been achieved and were not considered probable of achievement, as well as any potential sublicense fees or royalties on sales of licensed products, which will be recognized in the period of the underlying sales or sublicenses. The transaction price of the original March 2014 License increased by $3.5 million during the three and six months ended June 30, 2019 as a result of development milestones achieved during the period which were previously excluded from the transaction price.

Upon its execution, the transaction price of the January 2018 Amendment was $132.1 million, which was fully recognized as license revenue upon the delivery of the modified license in January 2018. In May 2018, as a result of the acquisition of AveXis by Novartis, the transaction price was increased by $40.0 million to account for the acceleration of the sale-based milestone which was previously excluded from the transaction price. The $40.0 million increase in the transaction price was recognized as license revenue upon the completion of the change of control in May 2018 since the amended license had been fully delivered to AveXis. Additionally, due to the acceleration of the two $30.0 million payments originally due in January 2019 and January 2020, the Company recognized $6.1 million of interest income from licensing upon the completion of the change of control of AveXis, which represents the remaining present value discount on such payments as of the date of the change of control. As of June 30, 2019, the transaction price of the January 2018 Amendment was $172.1 million, which includes: (i) the $80.0 million payment in January 2018, (ii) the present value, as of the date of the January 2018 Amendment, of the two $30.0 million payments originally due in January 2019 and January 2020 and (iii) the $40.0 million sales-based milestone which was accelerated upon the change of control in May 2018. Variable consideration under the January 2018 Amendment, which has been excluded from the transaction price, includes the remaining sales-based milestone payment of $80.0 million, as well as any potential sublicense fees or royalties on sales of licensed products, which will be recognized in the period of the underlying sales or sublicenses. There were no increases in the transaction price of the January 2018 Amendment during the three and six months ended June 30, 2019.

The Company recognized the following amounts under the March 2014 License with AveXis, as amended, which include amounts from both the original March 2014 License and the January 2018 Amendment (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
License and royalty revenue	$	4,424	$	40,000	$	4,424	$	172,066
Interest income from licensing	$	7	$	6,752	$	15	$	7,950

As of June 30, 2019, the Company had recorded $1.1 million of accounts receivable from AveXis under the March 2014 License, as amended, of which $0.9 million were included in current assets and $0.2 million were included in non-current assets. As of December 31, 2018, the Company had recorded $0.2 million of accounts receivable from AveXis under the March 2014 License, as amended, of which less than $0.1 million were included in current assets and $0.2 million were included in non-current assets.

Stock-based Compensation - Summary of Stock Option Activity (Detail) - 2014 and 2015 Equity Incentive Plan [Member] $ / shares in Units, shares in Thousands, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares [Roll Forward]
Shares Outstanding, Beginning Balance \| shares	4,855
Shares, Granted \| shares	1,410
Shares, Exercised \| shares	(621)
Shares, Cancelled or forfeited \| shares	(190)
Shares Outstanding, Ending Balance \| shares	5,454	4,855
Shares, Exercisable \| shares	2,630
Shares, Vested and expected to vest \| shares	5,454
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted-average Exercise Price Outstanding, Beginning Balance \| $ / shares	$ 19.31
Weighted-average Exercise Price, Granted \| $ / shares	48.48
Weighted-average Exercise Price, Exercised \| $ / shares	8.24
Weighted-average Exercise Price, Cancelled or forfeited \| $ / shares	32.92
Weighted-average Exercise Price, Outstanding, Ending Balance \| $ / shares	27.64	$ 19.31
Weighted-average Exercise Price, Exercisable \| $ / shares	13.65
Weighted-average Exercise Price, Vested and expected to vest \| $ / shares	$ 27.64
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted-average Remaining Contractual Life (Years) Outstanding	7 years 9 months 18 days	7 years 7 months 6 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 9 months 18 days
Aggregate Intrinsic Value Outstanding \| $	$ 136,336	$ 118,185
Aggregate Intrinsic Value, Exercisable \| $	99,341
Aggregate Intrinsic Value, Vested and expected to vest \| $	$ 136,336

Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2019	Aug. 02, 2019
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Trading Symbol	RGNX
Entity Registrant Name	REGENXBIO Inc.
Entity Central Index Key	0001590877
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity File Number	001-37553
Entity Tax Identification Number	47-1851754
Entity Address, Address Line One	9600 Blackwell Road
Entity Address, Address Line Two	Suite 210
Entity Address, City or Town	Rockville
Entity Address, State or Province	MD
Entity Address, Postal Zip Code	20850
City Area Code	240
Local Phone Number	552-8181
Entity Common Stock, Shares Outstanding		36,806,632
Document Transition Report	false
Document Quarterly Report	true
Entity Interactive Data Current	Yes
Security Exchange Name	NASDAQ
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Entity Incorporation, State or Country Code	DE

Summary of Significant Accounting Policies (Policies)

6 Months Ended

Jun. 30, 2019

Accounting Policies [Abstract]

Basis of Presentation and Principles of Consolidation

Use of Estimates

Reclassifications

Restricted Cash

	June 30, 2019		June 30, 2018
Cash and cash equivalents	$	55,142	$	106,889
Restricted cash		1,053		225
Total cash and cash equivalents and restricted cash	$	56,195	$	107,114

Marketable Securities

Leases

Fair Value of Financial Instruments

•

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.

Revenue Recognition

License and Royalty Revenue

Cost of Revenues

Net Income (Loss) Per Share

Recent Accounting Pronouncements

Adoption of ASU 2016-02, Leases

Other Recently Adopted Accounting Pronouncements

Recent Accounting Pronouncements Not Yet Adopted

Leases (Tables)

6 Months Ended

Jun. 30, 2019

Leases [Abstract]

Summary of Lease Costs and Supplemental Cash Flow Information of Operating Leases

The following table summarizes the Company’s lease costs and supplemental cash flow information related to operating leases (in thousands):

	Three Months Ended			Six Months Ended
	June 30, 2019			June 30, 2019
Operating lease cost	$	697		$	1,398
Variable lease cost		138			298
Total lease cost	$	835		$	1,696

Cash paid for amounts included in operating lease liabilities	$	684		$	1,395
Right-of-use assets acquired through operating lease liabilities	$	(371	)	$	(335	)

Weighted-Average Remaining Lease Term and Weighted-Average Discount Rate of Operating Leases

The weighted-average remaining lease term and weighted-average discount rate of the Company’s operating leases were as follows:

Reconciliation of Undiscounted Future Minimum Lease Payments Remaining Under Leases that Have Not Yet Commenced and Other Operating Leases

The following table presents a reconciliation of the undiscounted future minimum lease payments remaining under leases that have not yet commenced and other operating leases to the amounts reported as operating lease liabilities on the consolidated balance sheet as of June 30, 2019 (in thousands):

	Leases		Other			Total
	Not Yet		Operating			Minimum Lease
	Commenced (a)		Leases			Payments
Undiscounted future minimum lease payments:
2019 (remainder of year)	$	98	$	1,200		$	1,298
2020		460		2,813			3,273
2021		2,308		2,412			4,720
2022		5,422		623			6,045
2023		6,376		479			6,855
Thereafter		83,650		—			83,650
Total undiscounted future minimum lease payments	$	98,314	$	7,527		$	105,841
Amount representing imputed interest				(597	)
Total operating lease liabilities				6,930
Current portion of operating lease liabilities				(2,276	)
Operating lease liabilities, non-current			$	4,654

(a)

Includes undiscounted future minimum lease payments under the 9800 Medical Center Drive Lease and 400 Madison Lease which are not included in the lease liabilities reported on the consolidated balance sheet as of June 30, 2019. The actual timing and amounts of these payments are subject to adjustment based on the commencement dates and actual square footage of the leased premises. Accordingly, these amounts were estimates as of June 30, 2019.

Schedule of Future Minimum Lease Payments Under Topic 840 for 9800 Medical Center Drive Lease and Other Operating Leases

As of December 31, 2018, future minimum lease payments under Topic 840 for the 9800 Medical Center Drive Lease and other operating leases were as follows (in thousands):

	9800 Medical		Other		Total
	Center Drive		Operating		Minimum Lease
	Lease (a)		Leases		Payments
2019	$	—	$	2,798	$	2,798
2020		—		3,054		3,054
2021		1,329		2,391		3,720
2022		4,289		621		4,910
2023		5,156		479		5,635
Thereafter		76,420		—		76,420
Total minimum lease payments	$	87,194	$	9,343	$	96,537

(a)

Includes all future minimum lease payments under the 9800 Medical Center Drive Lease, including amounts recorded as financing lease obligations on the consolidated balance sheet. The actual timing and amounts of payments under the 9800 Medical Center Drive Lease are subject to adjustment based on the commencement date and actual square footage of the leased premises. Accordingly, these amounts were estimates as of December 31, 2018.

License and Royalty Revenue (Tables)

6 Months Ended

Jun. 30, 2019

License Agreement Revenue Recognition [Abstract]

Summary of Changes in Balances of Receivables, Contract Assets and Contract Liabilities

The following tables present changes in the balances of the Company’s receivables, contract assets and contract liabilities during the periods presented (in thousands):

	Balance at
	Beginning		Net Additions			Balance at
	of Period		(Deductions)			End of Period
Three Months Ended June 30, 2019
Receivables and contract assets:
Accounts receivable, current and non-current	$	31,130	$	2,504		$	33,634
Contract assets	$	1,000	$	(1,000	)	$	—
Contract liabilities:
Deferred revenue, current and non-current	$	3,933	$	(600	)	$	3,333

	Balance at
	Beginning		Net Additions			Balance at
	of Period		(Deductions)			End of Period
Six Months Ended June 30, 2019
Receivables and contract assets:
Accounts receivable, current and non-current	$	31,599	$	2,035		$	33,634
Contract assets	$	750	$	(750	)	$	—
Contract liabilities:
Deferred revenue, current and non-current	$	3,933	$	(600	)	$	3,333

	Balance at
	Beginning		Net Additions			Balance at
	of Period		(Deductions)			End of Period
Three Months Ended June 30, 2018
Receivables and contract assets:
Accounts receivable, current and non-current	$	58,621	$	(53,397	)	$	5,224
Contract assets	$	250	$	(250	)	$	—
Contract liabilities:
Deferred revenue, current and non-current	$	—	$	600		$	600

	Balance at
	Beginning		Net Additions			Balance at
	of Period		(Deductions)			End of Period
Six Months Ended June 30, 2018
Receivables and contract assets:
Accounts receivable, current and non-current	$	5,850	$	(626	)	$	5,224
Contract assets	$	350	$	(350	)	$	—
Contract liabilities:
Deferred revenue, current and non-current	$	—	$	600		$	600

Schedule of License Revenue

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
License and royalty revenue	$	4,424	$	40,000	$	4,424	$	172,066
Interest income from licensing	$	7	$	6,752	$	15	$	7,950

Marketable Securities (Tables)

6 Months Ended

Jun. 30, 2019

Investments Debt And Equity Securities [Abstract]

Summary of Company Marketable Securities

The following tables present a summary of the Company’s marketable securities, which consist of available-for-sale debt securities and equity securities (in thousands):

	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
June 30, 2019
U.S. government and federal agency securities	$	102,825	$	388	$	—		$	103,213
Certificates of deposit		8,748		67		—			8,815
Corporate bonds		249,377		1,070		(3	)		250,444
Equity securities		420		31,656		—			32,076
	$	361,370	$	33,181	$	(3	)	$	394,548

	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
December 31, 2018
U.S. government and federal agency securities	$	103,410	$	93	$	(37	)	$	103,466
Certificates of deposit		8,992		—		—			8,992
Corporate bonds		282,902		36		(377	)		282,561
	$	395,304	$	129	$	(414	)	$	395,019

Summary of Fair Values and Unrealized Losses of Marketable Securities Held by the Company in an Unrealized Loss Position for Less Than 12 months and 12 Months or Greater

The following tables present the fair values and unrealized losses of available-for-sale debt securities held by the Company in an unrealized loss position for less than 12 months and 12 months or greater (in thousands):

	Less than 12 Months					12 Months or Greater				Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
June 30, 2019
Corporate bonds	$	19,176	$	(3	)	$	—	$	—	$	19,176	$	(3	)
	$	19,176	$	(3	)	$	—	$	—	$	19,176	$	(3	)

	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	)

Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenues
Revenues	$ 7,881	$ 40,031	$ 8,765	$ 172,422
Type of Revenue [Extensible List]	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Operating Expenses
Cost of revenues	$ 1,927	$ 3,872	$ 1,956	$ 6,280
Research and development	29,483	21,486	54,686	41,036
General and administrative	13,405	8,318	24,963	16,698
Total operating expenses	44,753	33,681	81,543	64,047
Other operating expenses (income)	(62)	5	(62)	33
Income (loss) from operations	(36,872)	6,350	(72,778)	108,375
Other Income
Interest income from licensing	762	6,898	1,375	8,253
Investment income	34,524	1,196	37,519	2,055
Total other income	35,286	8,094	38,894	10,308
Income (loss) before income taxes	(1,586)	14,444	(33,884)	118,683
Income Tax Benefit (Expense)	129	(3,850)	199	(3,850)
Net income (loss)	(1,457)	10,594	(33,685)	114,833
Other Comprehensive Income (Loss)
Unrealized gain (loss) on available-for-sale securities, net of reclassifications and income tax expense	530	132	1,151	(56)
Total other comprehensive income (loss)	530	132	1,151	(56)
Comprehensive income (loss)	(927)	10,726	(32,534)	114,777
Net income (loss) applicable to common stockholders	$ (1,457)	$ 10,594	$ (33,685)	$ 114,833
Net income (loss) per share:
Basic	$ (0.04)	$ 0.33	$ (0.92)	$ 3.60
Diluted	$ (0.04)	$ 0.30	$ (0.92)	$ 3.29
Weighted-average common shares outstanding:
Basic	36,669	32,082	36,518	31,858
Diluted	36,669	35,272	36,518	34,884

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		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Basic net income (loss) per share:
Net income (loss) applicable to common stockholders	$ (1,457)	$ 10,594	$ (33,685)	$ 114,833
Shares used in computation:
Weighted-average common shares outstanding	36,669	32,082	36,518	31,858
Basic net income (loss) per share	$ (0.04)	$ 0.33	$ (0.92)	$ 3.60
Diluted net income (loss) per share:
Net income (loss) applicable to common stockholders	$ (1,457)	$ 10,594	$ (33,685)	$ 114,833
Shares used in computation:
Weighted-average common shares outstanding	36,669	32,082	36,518	31,858
Weighted-average diluted common shares	36,669	35,272	36,518	34,884
Diluted net income (loss) per share	$ (0.04)	$ 0.30	$ (0.92)	$ 3.29
Stock Option [Member]
Shares used in computation:
Weighted-average diluted common shares		3,153		2,995
Restricted Stock Units [Member]
Shares used in computation:
Weighted-average diluted common shares		30		27
Employee Stock Purchase Plan [Member]
Shares used in computation:
Weighted-average diluted common shares		7		4

Net Income (Loss) Per Share (Tables)

6 Months Ended

Jun. 30, 2019

Earnings Per Share [Abstract]

Computations of Basic and Diluted Net Income (Loss) Per Share

The computations of basic and diluted net income (loss) per share are as follows (in thousands, except per share data):

	Three Months Ended June 30,					Six Months Ended June 30,
	2019			2018		2019			2018
Basic net income (loss) per share:
Net income (loss) applicable to common stockholders	$	(1,457	)	$	10,594	$	(33,685	)	$	114,833
Shares used in computation:
Weighted-average common shares outstanding		36,669			32,082		36,518			31,858
Basic net income (loss) per share	$	(0.04	)	$	0.33	$	(0.92	)	$	3.60
Diluted net income (loss) per share:
Net income (loss) applicable to common stockholders	$	(1,457	)	$	10,594	$	(33,685	)	$	114,833
Shares used in computation:
Weighted-average common shares outstanding		36,669			32,082		36,518			31,858
Stock options		—			3,153		—			2,995
Restricted stock units		—			30		—			27
Employee stock purchase plan		—			7		—			4
Weighted-average diluted common shares		36,669			35,272		36,518			34,884
Diluted net income (loss) per share	$	(0.04	)	$	0.30	$	(0.92	)	$	3.29

Schedules for Computation of Diluted Weighted-Average Shares Outstanding

The following potentially dilutive common stock equivalents outstanding at the end of the period were excluded from the computations of weighted-average diluted common shares for the periods indicated as their effects would be anti-dilutive (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Stock options issued and outstanding		5,454		804		5,454		1,236
Unvested restricted stock units outstanding		40		—		40		—
Employee stock purchase plan		26		—		26		—
		5,520		804		5,520		1,236

Marketable Securities

6 Months Ended

Jun. 30, 2019

Investments Debt And Equity Securities [Abstract]

Marketable Securities

3. Marketable Securities

The following tables present a summary of the Company’s marketable securities, which consist of available-for-sale debt securities and equity securities (in thousands):

	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
June 30, 2019
U.S. government and federal agency securities	$	102,825	$	388	$	—		$	103,213
Certificates of deposit		8,748		67		—			8,815
Corporate bonds		249,377		1,070		(3	)		250,444
Equity securities		420		31,656		—			32,076
	$	361,370	$	33,181	$	(3	)	$	394,548

	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
December 31, 2018
U.S. government and federal agency securities	$	103,410	$	93	$	(37	)	$	103,466
Certificates of deposit		8,992		—		—			8,992
Corporate bonds		282,902		36		(377	)		282,561
	$	395,304	$	129	$	(414	)	$	395,019

As of June 30, 2019 and December 31, 2018, no available-for-sale debt securities had remaining maturities greater than three years. The amortized cost of marketable debt securities is adjusted for amortization of premiums and accretion of discounts to maturity, or to the earliest call date for callable debt securities purchased at a premium.

As of June 30, 2019 and December 31, 2018, the balance in the Company’s accumulated other comprehensive income (loss) consisted solely of net unrealized gains and losses on available-for-sale debt securities, net of income tax effects and reclassification adjustments for realized gains and losses. During the three and six months ended June 30, 2019, the Company recognized net unrealized gains on available-for-sale debt securities of $0.8 million and $1.8 million, respectively, and income tax expense of $0.3 million and $0.7 million, respectively, in other comprehensive income for the periods. The Company recognized net realized gains of zero and less than $0.1 million, respectively, on the sale or maturity of available-for-sale debt securities during the three and six months ended June 30, 2019, respectively, which were reclassified out of accumulated other comprehensive income (loss) during the periods and are included in investment income in the consolidated statements of operations and comprehensive income (loss). During the three and six months ended June 30, 2018, the Company recognized net unrealized gains (losses) on available-for-sale debt securities of $0.1 million and $(0.1) million, respectively, and income tax expense of zero in other comprehensive income (loss) for the periods. The Company did not recognize any realized gains or losses on the sale or maturity of available-for-sale debt securities during the three and six months ended June 30, 2018. Realized gains and losses from the sale or maturity of available-for-sale debt securities are determined based on the specific identification method.

	Less than 12 Months					12 Months or Greater				Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
June 30, 2019
Corporate bonds	$	19,176	$	(3	)	$	—	$	—	$	19,176	$	(3	)
	$	19,176	$	(3	)	$	—	$	—	$	19,176	$	(3	)

	Less than 12 Months					12 Months or Greater					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
December 31, 2018
U.S. government and federal agency securities	$	53,124	$	(37	)	$	—	$	—		$	53,124	$	(37	)
Corporate bonds		245,283		(354	)		12,424		(23	)		257,707		(377	)
	$	298,407	$	(391	)	$	12,424	$	(23	)	$	310,831	$	(414	)

As of June 30, 2019, available-for-sale debt securities held by the Company which were in an unrealized loss position consisted of 5 investment grade security positions. The Company has the intent and ability to hold such securities until recovery and has determined that none of the securities were other-than-temporarily impaired as of June 30, 2019 or December 31, 2018.

Marketable equity securities held by the Company as of June 30, 2019 consist solely of common stock of Prevail Therapeutics Inc. (Prevail). The Company acquired the securities as consideration for a commercial license to the NAV Technology Platform granted to Prevail in August 2017. Prevail completed its initial public offering (IPO) in June 2019. Prior to Prevail’s IPO, the securities were accounted for as non-marketable equity securities without a readily determinable fair value and had a carrying value of $0.4 million. Upon Prevail’s IPO in June 2019, the securities were reclassified to marketable securities and are measured at fair value. The Company recorded an unrealized gain of $31.7 million during the three and six months ended June 30, 2019 related to the marketable equity securities of Prevail, which is included in investment income in the consolidated statements of operations and comprehensive income (loss). Pursuant to a lock-up agreement executed in connection with Prevail’s IPO, the Company is restricted from selling its common stock of Prevail prior to December 2019. As of June 30, 2019, no amounts have been realized by the Company related to its marketable securities of Prevail as there have been no sales of the securities.

Stock-based Compensation (Tables)

6 Months Ended

Jun. 30, 2019

Stock-Based Compensation Expense by Award Type

The Company’s stock-based compensation expense by award type was as follows (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Stock options	$	6,844	$	3,818	$	12,296	$	6,939
Restricted stock units		69		69		136		136
Employee stock purchase plan		186		95		385		197
	$	7,099	$	3,982	$	12,817	$	7,272

Stock-Based Compensation Expense

The Company has recorded aggregate stock-based compensation expense in the consolidated statements of operations and comprehensive income (loss) as follows (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Research and development	$	3,526	$	1,895	$	5,873	$	3,424
General and administrative		3,573		2,087		6,944		3,848
	$	7,099	$	3,982	$	12,817	$	7,272

Summary of Unvested RSUs Activity Under 2015 Plan

The following table summarizes restricted stock unit activity under the 2015 Plan (in thousands, except per share data):

			Weighted-
			average
			Grant Date
	Shares		Fair Value
Unvested balance at December 31, 2018		40	$	20.90
Granted		—	$	—
Vested		—	$	—
Forfeited		—	$	—
Unvested balance at June 30, 2019		40	$	20.90

2014 and 2015 Equity Incentive Plan [Member]

Summary of Stock Option Activity

The following table summarizes stock option activity under the 2014 Plan and 2015 Plan (in thousands, except per share data):

						Weighted-
						average
				Weighted-		Remaining
				average		Contractual		Aggregate
				Exercise		Life		Intrinsic
	Shares			Price		(Years)		Value (a)
Outstanding at December 31, 2018		4,855		$	19.31		7.6	$	118,185
Granted		1,410		$	48.48
Exercised		(621	)	$	8.24
Cancelled or forfeited		(190	)	$	32.92
Outstanding at June 30, 2019		5,454		$	27.64		7.8	$	136,336
Exercisable at June 30, 2019		2,630		$	13.65		6.7	$	99,341
Vested and expected to vest at June 30, 2019		5,454		$	27.64		7.8	$	136,336

(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.

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Cash flows from operating activities
Net income (loss)	$ (33,685)	$ 114,833
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities
Stock-based compensation expense	12,817	7,272
Net amortization of premiums and accretion of discounts on marketable debt securities	(788)	718
Depreciation and amortization	3,363	1,730
Imputed interest income from licensing	(1,375)	(8,253)
Unrealized gains on marketable equity securities	31,656
Other non-cash adjustments	442	13
Changes in operating assets and liabilities
Accounts receivable	(1,419)	8,879
Prepaid expenses	(534)	1,644
Other current assets	1,419	(585)
Operating lease right-of-use assets	1,156
Other assets	(1,350)	(652)
Accounts payable	1,774	(340)
Accrued expenses and other current liabilities	(957)	2,566
Deferred revenue	(600)	600
Operating lease liabilities	(1,171)
Deferred rent		19
Other liabilities	(482)	(99)
Net cash provided by (used in) operating activities	(53,046)	128,345
Cash flows from investing activities
Purchases of marketable securities	(106,119)	(139,081)
Maturities of marketable securities	141,262	68,645
Purchases of property and equipment	(8,010)	(5,017)
Net cash provided by (used in) investing activities	27,133	(75,453)
Cash flows from financing activities
Proceeds from exercise of stock options	5,129	6,999
Proceeds from issuance of common stock under employee stock purchase plan	365	342
Net cash provided by financing activities	5,494	7,341
Net increase (decrease) in cash and cash equivalents and restricted cash	(20,419)	60,233
Cash and cash equivalents and restricted cash
Beginning of period	76,614	46,881
End of period	$ 56,195	$ 107,114

Leases - Additional Information (Detail)	1 Months Ended						3 Months Ended	6 Months Ended
Leases - Additional Information (Detail)	May 31, 2019 USD ($)	Nov. 30, 2018 USD ($) ft²	Apr. 30, 2018 USD ($)	May 31, 2016 USD ($)	Jan. 31, 2016 USD ($)	Mar. 31, 2015	Jun. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)
Other Commitments [Line Items]
Property and equipment, net							$ 27,330,000	$ 27,330,000		$ 28,702,000
Financing lease obligation										$ 5,854,000
Operating lease liabilities								(1,171,000)
Decrease in right-of-use assets								$ (1,156,000)
Rockville, Maryland [Member]
Other Commitments [Line Items]
Operating leases expiration year								2022
9800 Medical Center Drive Lease [Member] \| Leasehold Improvements [Member]
Other Commitments [Line Items]
Property and equipment, net							4,800,000	$ 4,800,000
9800 Medical Center Drive Lease [Member] \| ASU 2016-02 [Member] \| Restatement Adjustment [Member]
Other Commitments [Line Items]
Property and equipment, net									$ (5,900,000)
Financing lease obligation									$ (5,900,000)
9800 Medical Center Drive Lease [Member] \| Rockville, Maryland [Member]
Other Commitments [Line Items]
Lease Expiration Term		16 years
Construction completion, description								The initial construction of the building is being conducted by the landlord and is expected to be completed in 2020
Tenant improvement allowance to be received		$ 15,300,000
Lease not yet commenced, option to extend the lease								true
Lease not yet commenced, additional lease term		10 years
Lease not yet commenced, option to terminate the lease								true
Lease not yet commenced, option to terminate the lease, description								the option to terminate the lease after 12 years from the delivery of the leased premises to the Company. If the Company elects to terminate the lease, it will be subject to a termination fee equal to the unamortized tenant improvement allowance, rent abatement and landlord commissions as of the termination date, bearing interest at 5% per annum, plus four months of base rent and operating expenses.
Minimum release term for option to terminate		12 years
Percentage of early termination fee		5.00%
Term of required base rent to be paid as termination fee		4 months
Frequency of periodic payment								Monthly payments under the 9800 Medical Center Drive Lease begin approximately 12 months from the delivery of the leased premises to the Company and escalate annually in accordance with the lease agreement.
Periodic payment term, from the delivery of leased premises		12 months
Letters of credit		$ 800,000
Number of square feet to be constructed \| ft²		139,000
9712 Medical Center Drive [Member] \| Rockville, Maryland [Member]
Other Commitments [Line Items]
Lease term commenced date						2015-04
Lease term								In September 2015, November 2015, July 2017 and April 2018, the Company amended the 9712 Medical Center Drive Lease to include additional office and laboratory space at 9714 Medical Center Drive, and ultimately extend the term of the lease to September 2021.
Operating lease, existence of option to extend the lease								true
Additional lease term under option to extend			6 years
Tenant improvement allowance received			$ 400,000
9600 Blackwell Road [Member] \| Rockville, Maryland [Member]
Other Commitments [Line Items]
Percentage of early termination fee					8.00%
Lease term commenced date					2016-02
Operating lease, existence of option to extend the lease								true
Additional lease term under option to extend					5 years
Tenant improvement allowance received					$ 800,000
Lease expiration date					Sep. 30, 2023
Required period to terminate lease after commencement period					67 months
400 Madison Avenue [Member] \| 400 Madison Lease [Member]
Other Commitments [Line Items]
Letters of credit				$ 200,000
Operating leases commencement year				2016-07
Operating lease expiration year	2020-10
400 Madison Avenue [Member] \| 400 Madison Lease [Member] \| Lease Amendment [Member]
Other Commitments [Line Items]
Tenant improvement allowance to be received	$ 700,000
Operating lease expiration year								2019-08
Operating leases expiration term	7 years 6 months
Operating lease liabilities							400,000	$ 400,000
Decrease in right-of-use assets							$ 400,000	$ 400,000

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)		6 Months Ended
	Jan. 01, 2019	Jun. 30, 2019	Dec. 31, 2018
Significant Accounting Policies [Line Items]
Impairment of available-for-sale securities deemed to be other-than-temporary		$ 0
Operating lease right-of-use assets		5,904,000
Property and equipment, net		27,330,000	$ 28,702,000
Accumulated deficit		$ (116,774,000)	$ (83,016,000)
ASU 2016-02 [Member]
Significant Accounting Policies [Line Items]
Operating lease right-of-use assets	$ 7,400,000
Operating lease liabilities	8,400,000
ASU 2016-02 [Member] \| Maximum [Member]
Significant Accounting Policies [Line Items]
Accumulated deficit	100,000
ASU 2016-02 [Member] \| Restatement Adjustment [Member]
Significant Accounting Policies [Line Items]
Current and noncurrent deferred rent liabilities	1,400,000
Prepaid expenses, other current assets and other assets	400,000
ASU 2016-02 [Member] \| Restatement Adjustment [Member] \| 9800 Medical Center Drive Lease [Member]
Significant Accounting Policies [Line Items]
Property and equipment, net	(5,900,000)
Financing lease obligation	(5,900,000)
ASU 2018-02 [Member] \| Maximum [Member]
Significant Accounting Policies [Line Items]
Reclassification of stranded tax effects of unrealized gains and losses on available-for-sale securities from accumulated other comprehensive income (loss) to accumulated deficit	$ 100,000

Stock-based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	6 Months Ended
	Jan. 31, 2019	Jun. 30, 2019	Jun. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation expense		$ 70,400
Unrecognized stock-based compensation, weighted-average period		3 years
Proceeds from exercise of stock options		$ 5,129	$ 6,999
2015 Equity Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Additional shares to be issued	1,444,808
Common stock shares authorized for issuance		10,933,221
Shares available for future grants		2,327,843
Weighted-average fair values of options granted		$ 32.24
Exercise of stock options, Shares		621,415
Total intrinsic value of options exercised		$ 25,500
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		159,339
Common stock shares issued to participants		10,241

Fair Value of Financial Instruments

6 Months Ended

Jun. 30, 2019

Fair Value Disclosures [Abstract]

Fair Value of Financial Instruments

4. Fair Value of Financial Instruments

Financial instruments reported at fair value on a recurring basis include cash equivalents and marketable securities. The following tables present the fair value of cash equivalents and marketable securities in accordance with the hierarchy discussed in Note 2 (in thousands):

	Quoted		Significant
	prices		other		Significant
	in active		observable		unobservable
	markets		inputs		inputs
	(Level 1)		(Level 2)		(Level 3)		Total
June 30, 2019
Cash equivalents:
Money market mutual funds	$	—	$	55,126	$	—	$	55,126
Total cash equivalents		—		55,126		—		55,126
Marketable securities:
U.S. government and federal agency securities		—		103,213		—		103,213
Certificates of deposit		—		8,815		—		8,815
Corporate bonds		—		250,444		—		250,444
Equity securities		32,076		—		—		32,076
Total marketable securities		32,076		362,472		—		394,548
Total cash equivalents and marketable securities	$	32,076	$	417,598	$	—	$	449,674

	Quoted		Significant
	prices		other		Significant
	in active		observable		unobservable
	markets		inputs		inputs
	(Level 1)		(Level 2)		(Level 3)		Total
December 31, 2018
Cash equivalents:
Money market mutual funds	$	—	$	75,542	$	—	$	75,542
Total cash equivalents		—		75,542		—		75,542
Marketable securities:
U.S. government and federal agency securities		—		103,466		—		103,466
Certificates of deposit		—		8,992		—		8,992
Corporate bonds		—		282,561		—		282,561
Total marketable securities		—		395,019		—		395,019
Total cash equivalents and marketable securities	$	—	$	470,561	$	—	$	470,561

There were no transfers of financial instruments between levels of the fair value hierarchy during the six months ended June 30, 2019.

Management estimates that the carrying amounts of its current accounts receivable, accounts payable and accrued expenses and other current liabilities approximate fair value due to the short-term nature of those instruments. Accounts receivable which contain non-current portions are recorded at their present values using a discount rate that is based on prevailing market rates and the credit profile of the licensee on the date the amounts are initially recorded. Management does not believe there have been any significant changes in market conditions or credit quality that would cause the discount rates initially used to be significantly different from those that would be used as of June 30, 2019 to determine the present value of the receivables. Accordingly, management estimates that the carrying value of its non-current accounts receivable approximates the fair value of those instruments.

Non-marketable equity securities are measured at cost less impairment, adjusted for observable price changes for identical or similar investments of the same issuer. As of December 31, 2018, non-marketable equity securities had a carrying value of $0.4 million and were included in other assets on the consolidated balance sheets. The Company did not identify any observable price changes or changes in circumstances that would have had an adverse effect on the fair value of the securities as of December 31, 2018. In June 2019, all of the Company’s non-marketable equity securities were reclassified to marketable securities and as of June 30, 2019, the Company did not hold any non-marketable equity securities. No remeasurements or impairment losses were recorded on non-marketable equity securities during the three and six months ended June 30, 2019 and 2018.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Leases

6 Months Ended

Jun. 30, 2019

Leases [Abstract]

Leases

6. Leases

9800 Medical Center Drive

In November 2018, the Company entered into a lease agreement, as amended in April 2019, for approximately 139,000 square feet of office and laboratory facilities in a new building to be constructed at 9800 Medical Center Drive in Rockville, Maryland (the 9800 Medical Center Drive Lease). The initial construction of the building is being conducted by the landlord and is expected to be completed in 2020, after which the leased premises will be delivered to the Company to make additional improvements to the building. Pursuant to the amended lease agreement, the Company will receive a $15.3 million tenant improvement allowance from the landlord to construct additional improvements to the leased premises. The lease expires approximately 16 years from delivery of the leased premises to the Company, subject to certain extension and termination options held by the Company. The Company has the option to extend the term of the lease for up to 10 additional years and the option to terminate the lease after 12 years from the delivery of the leased premises to the Company. If the Company elects to terminate the lease, it will be subject to a termination fee equal to the unamortized tenant improvement allowance, rent abatement and landlord commissions as of the termination date, bearing interest at 5% per annum, plus four months of base rent and operating expenses. Additionally, after the delivery of the leased premises under the 9800 Medical Center Drive Lease, the Company will have the option to terminate its lease at 9712 Medical Center Drive with six months’ notice. Monthly payments under the 9800 Medical Center Drive Lease begin approximately 12 months from the delivery of the leased premises to the Company and escalate annually in accordance with the lease agreement. As required by the lease agreement, the Company has provided the landlord with an irrevocable letter of credit of $0.8 million which the landlord may draw upon in the event of any uncured default by the Company under the terms of the lease.

The Company is involved in the construction project for the leased premises at 9800 Medical Center Drive, including having the responsibility to pay for a portion of the costs of non-normal tenant improvements such as finish work, mechanical, electrical and plumbing elements of the building, among other items. As of December 31, 2018, under the requirements of Topic 840, the Company was deemed the owner of the leased premises during the construction period for accounting purposes and certain estimated construction costs incurred and reported by the landlord were recorded as property and equipment, with a corresponding financing lease obligation, on the consolidated balance sheet. The Company has determined that it does not control the building during the construction period under the requirements of Topic 842. Accordingly, upon the adoption of Topic 842 on January 1, 2019, the Company derecognized property and equipment of $5.9 million for the cumulative costs of construction incurred by the landlord as well as the associated $5.9 million financing lease obligation. As of June 30, 2019, the Company had recorded $4.8 million of costs related to construction-in-progress at 9800 Medical Center Drive, which have been recorded as leasehold improvements within property and equipment on the consolidated balance sheets.

As of June 30, 2019, the right-of-use assets and lease liabilities related to the 9800 Medical Center Drive Lease have not been recorded on the Company’s consolidated balance sheets and will be measured and recognized on the commencement date of the lease, which is expected to occur in 2020 when the landlord delivers the newly constructed building to the Company.

Other Leases

In March 2015, the Company entered into an operating lease for office space at 9712 Medical Center Drive in Rockville, Maryland (the 9712 Medical Center Drive Lease). The lease term commenced in April 2015. Monthly payments under the lease began in October 2015 and escalate annually in accordance with the lease agreement.

In September 2015, November 2015, July 2017 and April 2018, the Company amended the 9712 Medical Center Drive Lease to include additional office and laboratory space at 9714 Medical Center Drive, and ultimately extend the term of the lease to September 2021. The Company has options to extend the term of the 9712 Medical Center Drive Lease for up to six additional years. Additionally, upon the commencement of the 9800 Medical Center Drive Lease, the Company will have the option to terminate the 9712 Medical Center Drive Lease with six months’ notice. The Company’s extension and termination options under the 9712 Medical Center Drive Lease have been excluded from the measurement of the right-of-use assets and lease liabilities for the lease as they are not reasonably certain of exercise. The Company received a $0.4 million tenant improvement allowance from the landlord which has been recorded as a reduction of the right-of-use assets for the lease and is amortized on a straight-line basis as a reduction of rent expense over the term of the lease.

In January 2016, the Company entered into an operating lease for its corporate headquarters at 9600 Blackwell Road in Rockville, Maryland (the Blackwell Road Lease). The lease commenced in February 2016 and expires in September 2023. In November 2017, the Blackwell Road Lease was amended to include additional office space for the remainder of the lease term. Monthly payments under the lease began in September 2016 and escalate annually in accordance with the lease agreement. The Company has an option to extend the term of the Blackwell Road Lease for up to five additional years and the option to terminate the lease after 67 months from the lease commencement date. If the Company elects to terminate the lease, it will be subject to a termination fee equal to the unamortized tenant improvement allowance, rent abatement and landlord costs and commissions as of the termination date, bearing interest at 8% per annum. The Company’s extension and termination options under the Blackwell Road Lease have been excluded from the measurement of the right-of-use assets and lease liabilities for the lease as they are not reasonably certain of exercise. The Company received a $0.8 million tenant improvement allowance from the landlord which has been recorded as a reduction of the right-of-use assets for the lease and is amortized on a straight-line basis as a reduction of rent expense over the term of the lease.

In May 2016, the Company entered into an operating lease for office space at 400 Madison Avenue in New York, New York (the 400 Madison Lease). The lease commenced in July 2016 and monthly payments under the lease began in October 2016 and escalate annually in accordance with the lease agreement. As required by the lease agreement, the Company has provided the landlord with an irrevocable letter of credit of $0.2 million which the landlord may draw upon in the event of any uncured default by the Company under the terms of the lease.

In May 2019, the 400 Madison Lease was amended to include additional office space and extend the term of the lease. Prior to the amendment, the lease was to expire in October 2020. Pursuant to the amendment, the Company will vacate the original leased premises in the third quarter of 2019, upon which the landlord will perform demolition of the original premises as well as the additional premises under the amended lease. Upon completion of the demolition, the landlord will deliver the entire expanded premises to the Company to make tenant improvements. The amended lease will expire approximately 7.5 years from the date the expanded premises are delivered to the Company, which is expected to occur in 2019. The Company will receive a $0.7 million tenant improvement allowance from the landlord to construct improvements to the leased premises.

As a result of the amendment in May 2019, the expiration of the lease term for the original premises under the 400 Madison Lease was adjusted from October 2020 to August 2019. Accordingly, the right-of-use assets and lease liabilities for the original premises were reduced by $0.4 million to account for the modification of the lease term. As of June 30, 2019, the Company does not have control of the additional leased premises under the amended lease and the right-of-use assets and lease liabilities have not been recorded on the Company’s consolidated balance sheets. The right-of-use assets and lease liabilities related to the expanded premises for the extended lease term will be measured and recognized upon the delivery of the expanded premises to the Company to make tenant improvements.

The Company leases additional office and laboratory facilities in Rockville, Maryland, as well as laboratory and other equipment, under operating leases with various expiration dates through 2022.

Operating Lease Information

All of the Company’s leases are classified as operating leases. The following table summarizes the Company’s lease costs and supplemental cash flow information related to operating leases (in thousands):

	Three Months Ended			Six Months Ended
	June 30, 2019			June 30, 2019
Operating lease cost	$	697		$	1,398
Variable lease cost		138			298
Total lease cost	$	835		$	1,696

Cash paid for amounts included in operating lease liabilities	$	684		$	1,395
Right-of-use assets acquired through operating lease liabilities	$	(371	)	$	(335	)

Right-of-use assets acquired through operating lease liabilities for the three and six months ended June 30, 2019 includes a reduction of $0.4 million related to the April 2019 amendment to the 400 Madison Lease for the adjustment of the lease term. Short-term lease expense for the three and six months ended June 30, 2019 was not material and is included in operating lease cost in the table above. Variable lease cost under the Company’s operating leases includes items such as common area maintenance, utilities, taxes and other charges.

The weighted-average remaining lease term and weighted-average discount rate of the Company’s operating leases were as follows:

	Leases		Other			Total
	Not Yet		Operating			Minimum Lease
	Commenced (a)		Leases			Payments
Undiscounted future minimum lease payments:
2019 (remainder of year)	$	98	$	1,200		$	1,298
2020		460		2,813			3,273
2021		2,308		2,412			4,720
2022		5,422		623			6,045
2023		6,376		479			6,855
Thereafter		83,650		—			83,650
Total undiscounted future minimum lease payments	$	98,314	$	7,527		$	105,841
Amount representing imputed interest				(597	)
Total operating lease liabilities				6,930
Current portion of operating lease liabilities				(2,276	)
Operating lease liabilities, non-current			$	4,654

(a)

As of December 31, 2018, future minimum lease payments under Topic 840 for the 9800 Medical Center Drive Lease and other operating leases were as follows (in thousands):

	9800 Medical		Other		Total
	Center Drive		Operating		Minimum Lease
	Lease (a)		Leases		Payments
2019	$	—	$	2,798	$	2,798
2020		—		3,054		3,054
2021		1,329		2,391		3,720
2022		4,289		621		4,910
2023		5,156		479		5,635
Thereafter		76,420		—		76,420
Total minimum lease payments	$	87,194	$	9,343	$	96,537

(a)

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

Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	36,752,000	36,120,000
Common stock, shares outstanding	36,752,000	36,120,000

Property and Equipment Net - Schedule of Property and Equipment (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Total property and equipment	$ 37,913	$ 35,939
Accumulated depreciation and amortization	(10,583)	(7,237)
Property and equipment, net	27,330	28,702
Lab Equipment [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	16,533	14,417
Computer Equipment and Software [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	2,342	2,002
Furniture and Fixtures [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	1,946	1,915
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	$ 17,092	11,751
Construction in Progress [Member]
Property Plant And Equipment [Line Items]
Total property and equipment		$ 5,854

Supplemental Disclosures - Schedules of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
Accrued personnel costs	$ 6,692	$ 9,484
Accrued external research and development expenses	4,925	4,274
Accrued sublicense fees and royalties	1,514	1,617
Accrued external general and administrative expenses	1,498	773
Accrued income taxes payable	564	726
Accrued purchases of property and equipment	397	221
Other accrued expenses and current liabilities	944	69
Accrued expenses and other current liabilities	$ 16,534	$ 17,164

Commitments and Contingencies - Additional Information (Detail) - USD ($)	Jun. 30, 2019	Apr. 30, 2019
European Patent Office Proceeding [Member]
Other Commitments [Line Items]
Liability related to third party opposition	$ 0
University of Pennsylvania [Member] \| Maximum [Member]
Other Commitments [Line Items]
Upfront fee, milestone fees		$ 20,500,000

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

Stock-based Compensation - Summary of Unvested RSUs Activity Under 2015 Plan (Detail) - Restricted Stock Units [Member] shares in Thousands	6 Months Ended
	Jun. 30, 2019 $ / shares shares
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

Property and Equipment Net - Additional Information (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Property and equipment, net	$ 27,330		$ 28,702
ASU 2016-02 [Member] \| Restatement Adjustment [Member] \| 9800 Medical Center Drive Lease [Member]
Property Plant And Equipment [Line Items]
Property and equipment, net		$ (5,900)

Marketable Securities - Additional Information (Detail)	3 Months Ended		6 Months Ended		12 Months Ended
Marketable Securities - Additional Information (Detail)	Jun. 30, 2019 USD ($) Security	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) Security	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Schedule Of Available For Sale Securities [Line Items]
Available for sale debt securities remaining maturities greater than three years	$ 0		$ 0		$ 0
Unrealized gains (losses) on available-for-sale debt securities, before tax	800,000	$ 100,000	1,800,000	$ (100,000)
Unrealized gains (losses) on available-for-sale debt securities, income tax expense	$ 300,000	0	$ 700,000	0
Number of investment grade fixed income debt security \| Security	5		5
Other-than-temporary impaired			$ 0		$ 0
Non-marketable equity securities, carrying value	$ 400,000		400,000
Marketable securities realized			0
Equity Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Marketable securities unrealized gain (loss)	31,700,000		31,700,000
Investment Income [Member] \| Maximum [Member]
Schedule Of Available For Sale Securities [Line Items]
Net realized gains or losses available for sale debt securities	$ 0	$ 0	$ 100,000	$ 0

Marketable Securities - Summary of Company Marketable Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 361,370	$ 395,304
Unrealized Gains	33,181	129
Unrealized Losses	(3)	(414)
Fair Value	394,548	395,019
U.S. Government and Federal Agency Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	102,825	103,410
Unrealized Gains	388	93
Unrealized Losses		(37)
Fair Value	103,213	103,466
Certificates of Deposit [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	8,748	8,992
Unrealized Gains	67
Fair Value	8,815	8,992
Corporate Bonds [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	249,377	282,902
Unrealized Gains	1,070	36
Unrealized Losses	(3)	(377)
Fair Value	250,444	$ 282,561
Equity Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	420
Unrealized Gains	31,656
Fair Value	$ 32,076

Leases - Weighted-Average Remaining Lease Term and Weighted-Average Discount Rate of Operating Leases (Detail)	Jun. 30, 2019
Leases [Abstract]
Weighted-average remaining lease term (years)	2 years 10 months 24 days
Weighted-average discount rate	5.60%

Fair Value of Financial Instruments - Schedule of Fair Value of Cash Equivalents and Marketable Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Marketable securities:
Fair Value	$ 394,548	$ 395,019
Cash Equivalents and Marketable Securities [Member]
Marketable securities:
Total cash equivalents and marketable securities	449,674	470,561
Corporate Bonds [Member]
Marketable securities:
Fair Value	250,444	282,561
Cash Equivalents [Member]
Cash equivalents:
Total cash equivalents	55,126	75,542
U.S. Government and Federal Agency Securities [Member]
Marketable securities:
Fair Value	103,213	103,466
Certificates of Deposit [Member]
Marketable securities:
Fair Value	8,815	8,992
Equity Securities [Member]
Marketable securities:
Fair Value	32,076
Money Market Mutual Funds [Member] \| Cash Equivalents [Member]
Cash equivalents:
Total cash equivalents	55,126	75,542
Quoted Prices in Active Markets (Level 1) [Member]
Marketable securities:
Fair Value	32,076
Quoted Prices in Active Markets (Level 1) [Member] \| Cash Equivalents and Marketable Securities [Member]
Marketable securities:
Total cash equivalents and marketable securities	32,076
Quoted Prices in Active Markets (Level 1) [Member] \| Equity Securities [Member]
Marketable securities:
Fair Value	32,076
Significant Other Observable Inputs (Level 2) [Member]
Marketable securities:
Fair Value	362,472	395,019
Significant Other Observable Inputs (Level 2) [Member] \| Cash Equivalents and Marketable Securities [Member]
Marketable securities:
Total cash equivalents and marketable securities	417,598	470,561
Significant Other Observable Inputs (Level 2) [Member] \| Corporate Bonds [Member]
Marketable securities:
Fair Value	250,444	282,561
Significant Other Observable Inputs (Level 2) [Member] \| Cash Equivalents [Member]
Cash equivalents:
Total cash equivalents	55,126	75,542
Significant Other Observable Inputs (Level 2) [Member] \| U.S. Government and Federal Agency Securities [Member]
Marketable securities:
Fair Value	103,213	103,466
Significant Other Observable Inputs (Level 2) [Member] \| Certificates of Deposit [Member]
Marketable securities:
Fair Value	8,815	8,992
Significant Other Observable Inputs (Level 2) [Member] \| Money Market Mutual Funds [Member] \| Cash Equivalents [Member]
Cash equivalents:
Total cash equivalents	$ 55,126	$ 75,542

Supplemental Disclosures - Additional Information (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
Other liabilities	$ 1,899	$ 2,505

Nature of Business - Additional Information (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Accumulated deficit	$ (116,774)	$ (83,016)
Cash, cash equivalents and marketable securities	$ 449,700

Leases - Reconciliation of Undiscounted Future Minimum Lease Payments Remaining Under Leases that Have Not Yet Commenced and Other Operating Leases (Detail) $ in Thousands	Jun. 30, 2019 USD ($)
Undiscounted future minimum lease payments:
2019 (remainder of year)	$ 1,298
2020	3,273
2021	4,720
2022	6,045
2023	6,855
Thereafter	83,650
Total undiscounted future minimum lease payments	105,841
Current portion of operating lease liabilities	(2,276)
Operating lease liabilities, non-current	4,654
Leases Not Yet Commenced [Member]
Undiscounted future minimum lease payments:
2019 (remainder of year)	98
2020	460
2021	2,308
2022	5,422
2023	6,376
Thereafter	83,650
Total undiscounted future minimum lease payments	98,314
Other Operating leases [Member]
Undiscounted future minimum lease payments:
2019 (remainder of year)	1,200
2020	2,813
2021	2,412
2022	623
2023	479
Total undiscounted future minimum lease payments	7,527
Amount representing imputed interest	(597)
Total operating lease liabilities	6,930
Current portion of operating lease liabilities	(2,276)
Operating lease liabilities, non-current	$ 4,654