0000950170-23-061144 | 10-Q | XBRL Viewer

Nature of Business	9 Months Ended
Sep. 30, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Business	1. Nature of Business REGENXBIO Inc. (the Company) is a clinical-stage biotechnology company seeking to improve lives through the curative potential of gene therapy. The Company has developed a broad pipeline of gene therapy product candidates using its proprietary adeno-associated virus (AAV) gene delivery platform (NAV Technology Platform), which consists of exclusive rights to over 100 novel AAV vectors, including AAV7, AAV8 and AAV9. In addition to its internal product development efforts, the Company also selectively licenses the NAV® Technology Platform to other leading biotechnology and pharmaceutical companies (NAV Technology Licensees). As of September 30, 2023, the NAV Technology Platform was being applied by NAV Technology Licensees in one commercially available product, Zolgensma®, and in the preclinical and clinical development of a number of other licensed products. Additionally, the Company has licensed intellectual property rights to collaborators for the joint development and commercialization of certain product candidates. The Company was formed in 2008 in the State of Delaware and is headquartered in Rockville, Maryland. The Company has incurred cumulative losses since inception and as of September 30, 2023, had generated an accumulated deficit of $642.2 million. The Company's ability to transition to recurring profitability is dependent upon achieving a level of revenues adequate to support its cost structure, which depends heavily on the successful development, approval and commercialization of its product candidates. The Company may never achieve recurring profitability, and unless and until it does, the Company will continue to need to raise additional capital, to the extent possible. As of September 30, 2023, the Company had cash, cash equivalents and marketable securities of $364.5 million, which management believes is sufficient to fund operations for at least the next 12 months from the date these consolidated financial statements were issued.

Nature of Business

9 Months Ended

Sep. 30, 2023

Organization, Consolidation and Presentation of Financial Statements [Abstract]

1. Nature of Business

REGENXBIO Inc. (the Company) is a clinical-stage biotechnology company seeking to improve lives through the curative potential of gene therapy. The Company has developed a broad pipeline of gene therapy product candidates using its proprietary adeno-associated virus (AAV) gene delivery platform (NAV Technology Platform), which consists of exclusive rights to over 100 novel AAV vectors, including AAV7, AAV8 and AAV9. In addition to its internal product development efforts, the Company also selectively licenses the NAV® Technology Platform to other leading biotechnology and pharmaceutical companies (NAV Technology Licensees). As of September 30, 2023, the NAV Technology Platform was being applied by NAV Technology Licensees in one commercially available product, Zolgensma®, and in the preclinical and clinical development of a number of other licensed products. Additionally, the Company has licensed intellectual property rights to collaborators for the joint development and commercialization of certain product candidates. The Company was formed in 2008 in the State of Delaware and is headquartered in Rockville, Maryland.

The Company has incurred cumulative losses since inception and as of September 30, 2023, had generated an accumulated deficit of $642.2 million. The Company's ability to transition to recurring profitability is dependent upon achieving a level of revenues adequate to support its cost structure, which depends heavily on the successful development, approval and commercialization of its product candidates. The Company may never achieve recurring profitability, and unless and until it does, the Company will continue to need to raise additional capital, to the extent possible. As of September 30, 2023, the Company had cash, cash equivalents and marketable securities of $364.5 million, which management believes is sufficient to fund operations for at least the next 12 months from the date these consolidated financial statements were issued.

Stock-based Compensation - Summary of Stock Option Activity (Detail) - 2014 and 2015 Equity Incentive Plan [Member] $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2023 USD ($) $ / shares shares	Dec. 31, 2022 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares [Roll Forward]
Shares Outstanding, Beginning Balance \| shares	7,668
Shares, Granted \| shares	1,699
Shares, Exercised \| shares	(171)
Shares, Cancelled or forfeited \| shares	(340)
Shares Outstanding, Ending Balance \| shares	8,856	7,668
Shares, Exercisable \| shares	6,011
Shares, Vested and expected to vest \| shares	8,856
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted-average Exercise Price Outstanding, Beginning Balance \| $ / shares	$ 34.43
Weighted-average Exercise Price, Granted \| $ / shares	21.93
Weighted-average Exercise Price, Exercised \| $ / shares	7.66
Weighted-average Exercise Price, Cancelled or forfeited \| $ / shares	35.42
Weighted-average Exercise Price, Outstanding, Ending Balance \| $ / shares	32.51	$ 34.43
Weighted-average Exercise Price, Exercisable \| $ / shares	34.48
Weighted-average Exercise Price, Vested and expected to vest \| $ / shares	$ 32.51
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted-average Remaining Contractual Life (Years) Outstanding	6 years 4 months 24 days	6 years 6 months
Weighted-average Remaining Contractual Life (Years), Exercisable	5 years 4 months 24 days
Weighted-average Remaining Contractual Life (Years), Vested and expected to vest	6 years 4 months 24 days
Aggregate Intrinsic Value Outstanding \| $	$ 6,443	$ 15,783
Aggregate Intrinsic Value, Exercisable \| $	6,443
Aggregate Intrinsic Value, Vested and expected to vest \| $	$ 6,443

Capitalization - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended	9 Months Ended
	Sep. 01, 2023	Jul. 07, 2023	Sep. 30, 2023	Sep. 30, 2023
Schedule of Capitalization [Line Items]
Proceeds from private placement				$ 4,874
Private Placement [Member]
Schedule of Capitalization [Line Items]
Proceeds from private placement		$ 4,900
At the Market Offering Program
Schedule of Capitalization [Line Items]
Aggregate offering price	$ 150,000
Common Stock [Member]
Schedule of Capitalization [Line Items]
Number of shares sold			257,000	257,000
Common Stock [Member] \| Private Placement [Member]
Schedule of Capitalization [Line Items]
Number of shares sold		257,466
Purchase price of share		$ 19.42
Common Stock [Member] \| At the Market Offering Program
Schedule of Capitalization [Line Items]
Number of shares sold				0

Marketable Securities - Summary of Company Marketable Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost / Cost	$ 318,033	$ 482,792
Unrealized Gains	1	1
Unrealized Losses	(6,553)	(14,543)
Fair Value	311,481	468,250
U.S. Government and Agency Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost / Cost	94,595	134,485
Unrealized Gains	1
Unrealized Losses	(2,045)	(3,492)
Fair Value	92,551	130,993
Certificates of Deposit [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost / Cost	6,573	7,555
Unrealized Gains		1
Unrealized Losses	(164)	(248)
Fair Value	6,409	7,308
Corporate Bonds [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost / Cost	216,865	340,752
Unrealized Losses	(4,344)	(10,803)
Fair Value	$ 212,521	$ 329,949

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
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+ Details

Marketable Securities

9 Months Ended

Sep. 30, 2023

Investments, Debt and Equity Securities [Abstract]

Marketable Securities

3. Marketable Securities

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


	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
September 30, 2023
U.S. government and agency securities	$	94,595	$	1	$	(2,045	)	$	92,551
Certificates of deposit		6,573		—		(164	)		6,409
Corporate bonds		216,865		—		(4,344	)		212,521
	$	318,033	$	1	$	(6,553	)	$	311,481


	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
December 31, 2022
U.S. government and agency securities	$	134,485	$	—	$	(3,492	)	$	130,993
Certificates of deposit		7,555		1		(248	)		7,308
Corporate bonds		340,752		—		(10,803	)		329,949
	$	482,792	$	1	$	(14,543	)	$	468,250

As of September 30, 2023 and December 31, 2022, no available-for-sale debt securities had remaining maturities greater than three years. The amortized cost of marketable debt securities is adjusted for amortization of premiums and accretion of discounts to maturity, or to the earliest call date for callable debt securities purchased at a premium.

As of September 30, 2023 and December 31, 2022, the balance in accumulated other comprehensive loss consisted solely of unrealized gains and losses on available-for-sale debt securities, net of reclassification adjustments for realized gains and losses and income tax effects. 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 loss. 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. Unrealized gain (loss) on available-for-sale securities, net, as presented in the consolidated statements of operations and comprehensive loss consisted of the following (in thousands):


	Three Months Ended September 30,					Nine Months Ended September 30,
	2023		2022			2023		2022
Unrealized gain (loss) before reclassifications	$	2,685	$	(3,493	)	$	7,988	$	(15,759	)
Realized losses (gains) reclassified to investment income		—		—			—		72
Unrealized gain (loss) on available-for-sale securities, net	$	2,685	$	(3,493	)	$	7,988	$	(15,687	)

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


	Less than 12 Months					12 Months or Greater					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
September 30, 2023
U.S. government and agency securities	$	23,688	$	(68	)	$	61,885	$	(1,977	)	$	85,573	$	(2,045	)
Certificates of deposit		2,411		(24	)		3,753		(140	)		6,164		(164	)
Corporate bonds		38,793		(109	)		173,728		(4,235	)		212,521		(4,344	)
	$	64,892	$	(201	)	$	239,366	$	(6,352	)	$	304,258	$	(6,553	)


	Less than 12 Months					12 Months or Greater					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
December 31, 2022
U.S. government and agency securities	$	91,498	$	(2,014	)	$	38,495	$	(1,478	)	$	129,993	$	(3,492	)
Certificates of deposit		4,484		(144	)		2,087		(104	)		6,571		(248	)
Corporate bonds		106,707		(3,866	)		223,242		(6,937	)		329,949		(10,803	)
	$	202,689	$	(6,024	)	$	263,824	$	(8,519	)	$	466,513	$	(14,543	)

As of September 30, 2023, available-for-sale debt securities held by the Company which were in an unrealized loss position consisted of 103 investment grade security positions. The Company has the intent and ability to hold such securities until recovery, and based on the credit quality of the issuers and low severity of each unrealized loss position relative to its amortized cost basis, the Company did not identify any credit losses associated with its available-for-sale debt securities. The Company did not record an allowance for credit losses on its available-for-sale debt securities as of September 30, 2023 or December 31, 2022. The Company did not recognize any impairment or credit losses on available-for-sale debt securities during the three and nine months ended September 30, 2023 and 2022.

Stock-based Compensation - Stock-Based Compensation Expense by Award Type (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 10,219	$ 10,245	$ 31,929	$ 31,380
Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	7,275	8,663	22,868	26,755
Restricted Stock Units (RSUs)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	2,843	1,458	8,475	3,970
Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 101	$ 124	$ 586	$ 655

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

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+ Details

Insider Trading Arrangements

9 Months Ended

Sep. 30, 2023

Trading Arrangements, by Individual

Material Terms of Trading Arrangement

The adoption or termination of contracts, instructions or written plans for the purchase or sale of our securities by our Section 16 officers and directors for the three months ended September 30, 2023, each of which is intended to satisfy the affirmative defense of Rule 10b5-1(c) ("Rule 10b5-1 Plan"), were as follows:


					Aggregate # of
					Securities to be
Name	Title	Action	Date Adopted	Expiration Date	Purchased/Sold
Stephen Pakola, M.D.	Executive Vice President, Chief Medical Officer	Adoption	9/14/2023	6/16/2024	239,339
Kenneth T. Mills	President and Chief Executive Officer	Adoption	9/19/2023	9/19/2025	375,000

Other than as described above, during the three months ended September 30, 2023, none of our directors or Section 16 reporting officers adopted or terminated any Rule 10b5-1 trading arrangement or non-Rule 10b5-1 trading arrangement (as such terms are defined in Item 408 of the SEC's Regulation S-K).

Stephen Pakola [Member]

Trading Arrangements, by Individual

Name

Stephen Pakola, M.D.

Title

Executive Vice President, Chief Medical Officer

Rule 10b5-1 Arrangement Adopted

true

Adoption Date

9/14/2023

Aggregate Available

239,339

Kenneth T Mills [Member]

Trading Arrangements, by Individual

Name

Kenneth T. Mills

Title

President and Chief Executive Officer

Rule 10b5-1 Arrangement Adopted

true

Adoption Date

9/19/2023

Aggregate Available

375,000

Directors or Section 16 Reporting Officers [Member]

Trading Arrangements, by Individual

Title

directors or Section 16 reporting officers

Rule 10b5-1 Arrangement Adopted

false

Non-Rule 10b5-1 Arrangement Adopted

false

Rule 10b5-1 Arrangement Terminated

false

Non-Rule 10b5-1 Arrangement Terminated

false

Marketable Securities - Summary of unrealized loss on available-for-sale securities, net, presented in the consolidated statements of operations and comprehensive loss (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Investments, Debt and Equity Securities [Abstract]
Unrealized gain (loss) before reclassifications	$ 2,685	$ (3,493)	$ 7,988	$ (15,759)
Realized losses (gains) reclassified to investment income				72
Unrealized gain (loss) on available-for-sale securities, net	$ 2,685	$ (3,493)	$ 7,988	$ (15,687)

Consolidated Statements of Stockholders' Equity (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2023
Common Stock [Member]
Issuance of Stock, transaction costs	$ 126	$ 126

Subsequent Events - Additional Information (Detail) - Subsequent Event [Member] - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Nov. 30, 2023	Dec. 31, 2023
Subsequent Event [Line Items]
Percentage of workforce reduction due to restructuring	15.00%
Restructuring costs		$ 3.6

Stock-based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	9 Months Ended
	Jan. 31, 2023	Sep. 30, 2023
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation expense		$ 73.0
Unrecognized stock-based compensation, weighted-average period		2 years 6 months
Proceeds from stock options exercised including unsettled options		$ 1.3
Restricted Stock Units (RSUs)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted stock units vested		179,000
Total intrinsic values vested		$ 3.8
2015 Equity Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Additional shares to be issued	1,731,940
Common stock shares authorized for issuance		17,357,140
Shares available for future grants		2,228,020
Weighted-average fair values of options granted		$ 13.68
Exercise of stock options, net of tax, shares		171,250
Total intrinsic value of options exercised		$ 2.1
2015 Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares authorized for issuance		1,426,994
Shares available for future grants		1,018,364
Common stock shares issued to participants		103,388

Summary of Significant Accounting Policies

9 Months Ended

Sep. 30, 2023

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, 2022 included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2022, which was filed with the SEC on February 28, 2023. 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, 2022, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2022.

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 the consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses and related disclosure of contingent assets and liabilities for the periods presented. Management bases its estimates on historical experience and various other factors that it believes are reasonable under the circumstances, the results of which form the basis for making judgments about the carrying value of assets and liabilities, and other reported amounts, that are not readily apparent from other sources. Actual results may differ materially from these estimates. Significant estimates are used in the following areas, among others: license and royalty revenue, the allowance for credit losses, accrued research and development expenses and other accrued liabilities, stock-based compensation expense, interest expense under the liability related to the sale of future royalties, 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 and other deposits used to collateralize irrevocable letters of credit required under the Company’s lease agreements and certain other agreements with third parties. 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):


	As of September 30,
	2023		2022
Cash and cash equivalents	$	53,045	$	118,544
Restricted cash		2,255		2,030
Total cash and cash equivalents and restricted cash	$	55,300	$	120,574

Accounts Receivable

Accounts receivable primarily consist of consideration due to the Company resulting from its license agreements with customers. Accounts receivable include amounts invoiced to licensees as well as rights to consideration which have not yet been invoiced, including unbilled royalties, and for which payment is conditional solely upon the passage of time. If a licensee elects to terminate a license prior to the end of the license term, the licensed intellectual property is returned to the Company and any accounts receivable from the licensee which are not contractually payable to the Company are charged off as a reduction of license revenue in the period of the termination. Accounts receivable which are not expected to be received by the Company within 12 months from the reporting date are stated net of a discount to present value and recorded as non-current assets on the consolidated balance sheets. The present value discount is recognized as a reduction of revenue in the period in which the accounts receivable are initially recorded and is accreted as interest income from licensing over the term of the receivables.

Accounts receivable are stated net of an allowance for credit losses, if deemed necessary based on the Company’s evaluation of collectability and potential credit losses. Management assesses the collectability of its accounts receivable using the specific identification of account balances, and considers the credit quality and financial condition of its significant customers, historical information regarding credit losses and the Company’s evaluation of current and expected future economic conditions. If necessary, an allowance for credit losses is recorded against accounts receivable such that the carrying value of accounts receivable reflects the net amount expected to be collected. Accounts receivable balances are written off against the allowance for credit losses when the potential for collectability is considered remote. Please refer to Note 9 for further information regarding the allowance for credit losses related to accounts receivable.

Fair Value of Financial Instruments

The Company is required to disclose information on all assets and liabilities reported at fair value that enables an assessment of the inputs used in determining the reported fair values. Accounting Standards Codification (ASC) 820, Fair Value Measurements and Disclosures, 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.

Net Loss Per Share

Basic net loss per share is calculated by dividing net loss applicable to common stockholders by the weighted-average common shares outstanding during the period, without consideration for common stock equivalents. Diluted net 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 loss per share until the contingency has been fully met. For purposes of the diluted net loss per share calculation, common stock equivalents are excluded from the calculation of diluted net loss per share if their effect would be anti-dilutive.

Fair Value of Financial Instruments

9 Months Ended

Sep. 30, 2023

Fair Value Disclosures [Abstract]

Fair Value of Financial Instruments

4. Fair Value of Financial Instruments

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


	Quoted		Significant
	prices		other		Significant
	in active		observable		unobservable
	markets		inputs		inputs
	(Level 1)		(Level 2)		(Level 3)		Total
September 30, 2023
Cash equivalents:
Money market mutual funds	$	—	$	30,966	$	—	$	30,966
Total cash equivalents		—		30,966		—		30,966
Marketable securities:
U.S. government and agency securities		—		92,551		—		92,551
Certificates of deposit		—		6,409		—		6,409
Corporate bonds		—		212,521		—		212,521
Total marketable securities		—		311,481		—		311,481
Total cash equivalents and marketable securities	$	—	$	342,447	$	—	$	342,447


	Quoted		Significant
	prices		other		Significant
	in active		observable		unobservable
	markets		inputs		inputs
	(Level 1)		(Level 2)		(Level 3)		Total
December 31, 2022
Cash equivalents:
Money market mutual funds	$	—	$	58,611	$	—	$	58,611
Corporate bonds		—		993		—		993
Total cash equivalents		—		59,604		—		59,604
Marketable securities:
U.S. government and agency securities		—		130,993		—		130,993
Certificates of deposit		—		7,308		—		7,308
Corporate bonds		—		329,949		—		329,949
Total marketable securities		—		468,250		—		468,250
Total cash equivalents and marketable securities	$	—	$	527,854	$	—	$	527,854

Management estimates that the carrying values of its current accounts receivable, other current assets, accounts payable, 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 and certain non-current payables reported as other liabilities are recorded at their present values using a discount rate that is based on prevailing market rates on the date the amounts were 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 materially different from those that would be used as of September 30, 2023 to determine the present value of these instruments. Accordingly, management estimates that the carrying values of its non-current accounts receivable and other liabilities approximate the fair value of those instruments. Management estimates that the carrying value of the liability related to the sale of future royalties approximates fair value. As discussed in Note 6, the carrying value of the liability related to the sale of future royalties is based on the Company’s estimate of future royalties expected to be paid by the Company over the life of the arrangement, which are considered Level 3 inputs.

Non-marketable Equity Securities

Non-marketable equity securities are measured at cost less impairment, adjusted for observable price changes for identical or similar investments of the same issuer. The Company did not hold any non-marketable equity securities as of September 30, 2023 and December 31, 2022. No remeasurements or impairment losses were recorded on non-marketable equity securities during the three and nine months ended September 30, 2023 and 2022.

Prior to the acquisition of Corlieve Therapeutics (SAS) (Corlieve) by uniQure N.V. (uniQure) in July 2021, the Company held non-marketable equity securities of Corlieve, which were originally acquired by the Company in June 2020 as consideration under a license and collaboration agreement with Corlieve. As a result of the acquisition of Corlieve by uniQure in July 2021, the Company received upfront proceeds of €5.3 million ($6.1 million) from uniQure in exchange for its ownership interest in Corlieve. Additionally, the Company became eligible to receive payments of up to €37.1 million from uniQure contingent upon the achievement of various development and regulatory milestones, of which €35.3 million ($37.3 million as of September 30, 2023) have not been paid or achieved as of September 30, 2023 and have not been recognized in the consolidated financial statements. During the three months ended September 30, 2023, the Company received €1.9 million from uniQure upon the achievement of milestones. The Company recognized investment income of $2.2 million related to these milestone payments during the three and nine months ended September 30, 2023. Proceeds contingent upon the achievement of the remaining milestones will be recognized as investment income in the period in which any uncertainty regarding realization is substantially resolved, which may not occur until the achievement of the underlying milestones. It is at least reasonably possible that some or all of the proceeds contingent upon these milestones will not be realized by the Company.

- 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

Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2023	Dec. 31, 2022
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	43,991,000	43,299,000
Common stock, shares outstanding	43,991,000	43,299,000

Liability Related to Sale of Future Royalties (Tables)

9 Months Ended

Sep. 30, 2023

Schedule of Changes in Liability Related to Sale of Future Royalties

The following table presents the changes in the liability related to the sale of future royalties under the Royalty Purchase Agreement with HCR (in thousands):


	Liability Related to
	Sale of Future Royalties
Balance at December 31, 2022	$	137,606
Zolgensma royalties paid to HCR		(36,614	)
Interest expense recognized		4,854
Balance at September 30, 2023		105,846
Current portion of liability related to sale of future royalties		(52,750	)
Non-current portion of liability related to sale of future royalties	$	53,096

Net Loss Per Share (Tables)

9 Months Ended

Sep. 30, 2023

Earnings Per Share [Abstract]

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 and Nine Months Ended September 30,
	2023		2022
Stock options issued and outstanding		8,856		7,774
Unvested restricted stock units outstanding		1,394		617
Employee stock purchase plan		36		26
		10,286		8,417

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Cash flows from operating activities
Net loss	$ (200,605)	$ (220,386)
Adjustments to reconcile net loss to net cash used in operating activities
Stock-based compensation expense	31,929	31,380
Depreciation and amortization	12,985	8,783
Net amortization of premiums on marketable debt securities	929	3,809
Net loss (gain) on investments	(2,205)	79
Imputed interest income from licensing	(166)	(264)
Non-cash interest expense	(569)	767
Other non-cash adjustments	165	540
Changes in operating assets and liabilities
Accounts receivable	566	(22)
Prepaid expenses	1,339	3,928
Other current assets	(13,573)	2,751
Operating lease right-of-use assets	4,245	3,083
Other assets	1,728	(1,922)
Accounts payable	(4,011)	16,883
Accrued expenses and other current liabilities	(1,546)	(28,241)
Deferred revenue	(1,218)	2,824
Operating lease liabilities	(5,004)	(50)
Other liabilities	(2,636)	7,942
Net cash used in operating activities	(177,647)	(168,116)
Cash flows from investing activities
Purchases of marketable debt securities	(67,925)	(172,910)
Maturities of marketable debt securities	231,753	159,011
Sales of equity securities	1,975	524
Purchases of property and equipment	(8,834)	(25,254)
Net cash provided by (used in) investing activities	156,969	(38,629)
Cash flows from financing activities
Proceeds from exercise of stock options	1,312	2,761
Taxes paid related to net settlement of stock-based awards	(419)	(284)
Proceeds from issuance of common stock under employee stock purchase plan	1,826	1,742
Proceeds from private placement of common stock, net of issuance costs	4,874
Offering expenses related to at-the-market offering program	(51)
Repayments under liability related to sale of future royalties, net of imputed interest	(30,546)	(24,139)
Net cash used in financing activities	(23,004)	(19,920)
Net decrease in cash and cash equivalents and restricted cash	(43,682)	(226,665)
Cash and cash equivalents and restricted cash
Beginning of period	98,982	347,239
End of period	$ 55,300	$ 120,574

Commitments and Contingencies

9 Months Ended

Sep. 30, 2023

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

7. Commitments and Contingencies

The Trustees of the University of Pennsylvania

In February 2009, the Company entered into a license agreement, which has been amended from time to time (as amended, the Penn License), with The Trustees of the University of Pennsylvania (together with the University of Pennsylvania, Penn) for exclusive, worldwide rights to certain patents owned by Penn underlying the Company’s NAV Technology Platform, as well as exclusive rights to certain data, results and other information. In March 2022, the Company and Penn entered into a letter agreement (the Penn Letter Agreement) pursuant to which the Company will pay to Penn a total of $20.0 million, consisting of (i) $8.0 million paid in April 2022 to satisfy payment of any sublicense fees due or owed in the future under the Penn License as a result of the Company’s collaboration and license agreement with AbbVie Global Enterprises Ltd., and (ii) $12.0 million to satisfy any other past or future obligations of the Company to pay sublicense fees under the Penn License, which is payable in four equal annual installments of $3.0 million beginning in March 2023. The Penn Letter Agreement amended the Penn License to remove the Company’s obligations to pay sublicense fees under the license agreement. The Company remains obligated to pay Penn royalties on net sales of licensed products, milestone fees and reimbursement of certain patent maintenance costs in accordance with the Penn License.

The Company recognized a charge of $9.2 million as cost of revenues upon the execution of Penn Letter Agreement in March 2022, which consisted of $17.3 million representing the present value of the $20.0 million payable under the Penn Letter Agreement, less $8.1 million in sublicense fees previously recognized as expense by the Company in prior periods and accrued as liabilities prior to the effectiveness of the Penn Letter Agreement. The present value discount is accreted as interest expense over the contractual payment period using the effective interest method. In addition to other amounts payable under the Penn License, as of September 30, 2023, the Company had recorded a total of $7.8 million payable under the Penn Letter Agreement, net of present value discount, of which $2.3 million was included in accrued expenses and other current liabilities and $5.5 million was included in other liabilities on the consolidated balance sheet.

License and Collaboration Agreements (Tables)

9 Months Ended

Sep. 30, 2023

Schedule Of License and Royalty Revenue

License and royalty revenue consisted of the following (in thousands):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022
Zolgensma royalties	$	28,364	$	25,205	$	63,454	$	75,130
Other license and royalty revenue		550		1,307		4,575		6,249
Total license and royalty revenue	$	28,914	$	26,512	$	68,029	$	81,379

Summary of Changes in Balances of Receivables, Contract Assets and Deferred Revenue

The following table presents the balances of the Company’s net accounts receivable, contract assets and deferred revenue, as well as other information regarding revenue recognized during the periods presented (in thousands):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022
Accounts receivable, net, current and non-current:
Beginning of period	$	22,523	$	39,534	$	29,586	$	34,701
End of period	$	29,121	$	34,352	$	29,121	$	34,352

Contract assets:
Beginning of period	$	2,000	$	—	$	—	$	1,074
End of period	$	2,000	$	—	$	2,000	$	—

Deferred revenue, current and non-current:
Beginning of period	$	448	$	6,636	$	1,829	$	3,333
End of period	$	442	$	5,903	$	442	$	5,903

Revenue recognized during the period from:
Amounts included in deferred revenue at beginning of period	$	28	$	1,343	$	1,409	$	—
Performance obligations satisfied in previous periods	$	28,365	$	25,169	$	65,405	$	75,130

Summary of Accounts Receivables, net

Accounts receivable, net consisted of the following (in thousands):


	September 30, 2023			December 31, 2022
Current accounts receivable:
Billed to customers	$	92		$	280
Unbilled Zolgensma royalties		27,311			27,027
Other unbilled		640			775
Allowance for credit losses		—			—
Current accounts receivable, net		28,043			28,082
Non-current accounts receivable:
Due from Abeona, net of present value discount		4,474			4,152
Other unbilled		1,078			1,504
Allowance for credit losses		(4,474	)		(4,152	)
Non-current accounts receivable, net		1,078			1,504
Total accounts receivable, net	$	29,121		$	29,586

Summary of Changes in Allowance For Credit Losses

The following table presents the changes in the allowance for credit losses related to accounts receivable and contract assets for the nine months ended September 30, 2023 (in thousands):


	Allowance for Credit Losses
	Accounts Receivable		Contract Assets
Balance at December 31, 2022	$	4,152	$	—
Changes in present value discount of receivables		322		—
Balance at September 30, 2023	$	4,474	$	—

Schedule of AbbVie Collaboration Agreement

The Company recognized the following amounts under the AbbVie Collaboration Agreement (in thousands):


	Three Months Ended September 30,						Nine Months Ended September 30,
	2023			2022			2023			2022
Net cost reimbursement to (from) AbbVie included in:
Research and development expense	$	(19,608	)	$	(4,245	)	$	(56,300	)	$	(12,339	)
General and administrative expense		615			750			1,007			954
Total net cost reimbursement to (from) AbbVie	$	(18,993	)	$	(3,495	)	$	(55,293	)	$	(11,385	)

Novartis Gene Therapies [Member]

Schedule Of License and Royalty Revenue

The Company recognized the following amounts under the Novartis License (in thousands):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022
Zolgensma royalties	$	28,364	$	25,205	$	63,454	$	75,130
Other license revenue		—		—		—		31
Total license and royalty revenue	$	28,364	$	25,205	$	63,454	$	75,161

Interest income from licensing	$	7	$	8	$	22	$	84

Supplemental Disclosures (Tables)

9 Months Ended

Sep. 30, 2023

Payables and Accruals [Abstract]

Schedule of Other Current Assets

Other Current Assets

Other current assets consisted of the following (in thousands):


	September 30, 2023		December 31, 2022
Net cost reimbursement due from collaborators	$	18,684	$	6,294
License revenue contract assets		2,000		—
Accrued interest on investments		1,673		2,210
Other		990		848
	$	23,347	$	9,352

Schedules of Accrued Expenses and Other Current Liabilities

Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following (in thousands):


	September 30, 2023		December 31, 2022
Accrued sublicense fees and royalties	$	15,022	$	15,768
Accrued personnel costs		14,864		18,071
Accrued external research and development expenses		11,681		9,216
Accrued external general and administrative expenses		2,759		2,187
Accrued purchases of property and equipment		469		806
Other accrued expenses and current liabilities		861		746
	$	45,656	$	46,794

Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2023	Nov. 02, 2023
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2023
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q3
Trading Symbol	RGNX
Entity Registrant Name	REGENXBIO Inc.
Entity Central Index Key	0001590877
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity File Number	001-37553
Entity Tax Identification Number	47-1851754
Entity Address, Address Line One	9804 Medical Center Drive
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		43,991,980
Document Transition Report	false
Document Quarterly Report	true
Entity Interactive Data Current	Yes
Security Exchange Name	NASDAQ
Title of 12(b) Security	Common Stock, par value $0.0001 per share
Entity Incorporation, State or Country Code	DE

Supplemental Disclosures

9 Months Ended

Sep. 30, 2023

Payables and Accruals [Abstract]

Supplemental Disclosures

14. Supplemental Disclosures

Other Current Assets

Other current assets consisted of the following (in thousands):


	September 30, 2023		December 31, 2022
Net cost reimbursement due from collaborators	$	18,684	$	6,294
License revenue contract assets		2,000		—
Accrued interest on investments		1,673		2,210
Other		990		848
	$	23,347	$	9,352

Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following (in thousands):


	September 30, 2023		December 31, 2022
Accrued sublicense fees and royalties	$	15,022	$	15,768
Accrued personnel costs		14,864		18,071
Accrued external research and development expenses		11,681		9,216
Accrued external general and administrative expenses		2,759		2,187
Accrued purchases of property and equipment		469		806
Other accrued expenses and current liabilities		861		746
	$	45,656	$	46,794

Supplemental Disclosures of Non-cash Investing and Financing Activities

Purchases of property and equipment included in accounts payable and accrued expenses and other current liabilities were $0.5 million as of September 30, 2023, a net decrease of $2.0 million from December 31, 2022, and $3.1 million as of September 30, 2022, a net decrease of $7.0 million from December 31, 2021.

Offering expenses for the ATM Program included in accounts payable and accrued expenses and other liabilities as of September 30, 2023 were $0.4 million. No such amounts were recorded as of September 30, 2022.

Marketable Securities - Additional Information (Detail)	3 Months Ended		9 Months Ended
Marketable Securities - Additional Information (Detail)	Sep. 30, 2023 USD ($) Security	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) Security	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)
Investments, Debt and Equity Securities [Abstract]
Available for sale debt securities remaining maturities greater than three years	$ 0		$ 0		$ 0
Number of investment grade fixed income debt security \| Security	103		103
Allowance for credit loss	$ 0		$ 0		$ 0
Other-than-temporary impaired	$ 0	$ 0	$ 0	$ 0

Capitalization

9 Months Ended

Sep. 30, 2023

Equity [Abstract]

Capitalization

8. Capitalization

Private Placement

On July 7, 2023, the Company sold an aggregate of 257,466 shares of its common stock to Redmile Biopharma Investments III, L.P. (Redmile) at a purchase price of $19.42 per share, which was the closing price of the common stock on July 6, 2023 (the Private Placement). The Company received aggregate net proceeds from the Private Placement of $4.9 million, net of offering expenses. The Private Placement was conducted in reliance on the exemption from registration provided by Section 4(a)(2) of the Securities Act.

At-the-Market Offering Program

On September 1, 2023, the Company entered into an ATM Equity OfferingSM Sales Agreement with BofA Securities, Inc. (BofA) pursuant to which the Company may offer and sell shares of its common stock having an aggregate offering price of up to $150.0 million from time to time through BofA, acting as the Company's sales agent (the ATM Program). As of September 30, 2023, no shares of common stock had been sold under the ATM Program.

- Definition

The entire disclosure for equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-14

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481004/946-505-50-6

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480237/815-40-50-6

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480008/505-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(e)(1))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 505
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//505/tableOfContent

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-14

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-14

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 16
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-16

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

+ Details

Net Loss Per Share - Schedules for Computation of Diluted Weighted-Average Shares Outstanding (Detail) - shares shares in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted weighted average shares outstanding	10,286	8,417
Stock Options Issued and Outstanding [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted weighted average shares outstanding	8,856	7,774
Unvested Restricted Stock Units Outstanding [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted weighted average shares outstanding	1,394	617
Employee Stock Purchase Plan [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted weighted average shares outstanding	36	26

Stock-based Compensation

9 Months Ended

Sep. 30, 2023

Share-Based Payment Arrangement [Abstract]

Stock-based Compensation

10. Stock-based Compensation

Effective January 2023, an additional 1,731,940 shares were authorized for issuance under the 2015 Equity Incentive Plan (the 2015 Plan). As of September 30, 2023, the total number of shares of common stock authorized for issuance under the 2015 Plan and the 2014 Stock Plan (the 2014 Plan) was 17,357,140, of which 2,228,020 remained available for future grants under the 2015 Plan.

Stock-based Compensation Expense

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


	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022
Stock options	$	7,275	$	8,663	$	22,868	$	26,755
Restricted stock units		2,843		1,458		8,475		3,970
Employee stock purchase plan		101		124		586		655
	$	10,219	$	10,245	$	31,929	$	31,380

As of September 30, 2023, the Company had $73.0 million of unrecognized stock-based compensation expense related to stock options, restricted stock units and the 2015 Employee Stock Purchase Plan (the 2015 ESPP), which is expected to be recognized over a weighted-average period of 2.5 years.

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


	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022
Research and development	$	5,131	$	5,351	$	16,670	$	16,426
General and administrative		5,088		4,894		15,259		14,954
	$	10,219	$	10,245	$	31,929	$	31,380

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, 2022		7,668		$	34.43		6.5	$	15,783
Granted		1,699		$	21.93
Exercised		(171	)	$	7.66
Cancelled or forfeited		(340	)	$	35.42
Outstanding at September 30, 2023		8,856		$	32.51		6.4	$	6,443
Exercisable at September 30, 2023		6,011		$	34.48		5.4	$	6,443
Vested and expected to vest at September 30, 2023		8,856		$	32.51		6.4	$	6,443

(a) The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying options and the fair value of the common stock for the options that were in the money at the dates reported.

The weighted-average grant date fair value per share of options granted during the nine months ended September 30, 2023 was $13.68. During the nine months ended September 30, 2023, the total number of stock options exercised was 171,250, resulting in total proceeds of $1.3 million. The total intrinsic value of options exercised during the nine months ended September 30, 2023 was $2.1 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, 2022		613		$	35.41
Granted		1,029		$	22.07
Vested		(179	)	$	35.18
Forfeited		(69	)	$	27.16
Unvested balance at September 30, 2023		1,394		$	26.00

The total intrinsic value of restricted stock units vested during the nine months ended September 30, 2023 was $3.8 million.

Employee Stock Purchase Plan

As of September 30, 2023, the total number of shares of common stock authorized for issuance under the 2015 ESPP was 1,426,994, of which 1,018,364 remained available for future issuance. During the nine months ended September 30, 2023, 103,388 shares of common stock were issued under the 2015 ESPP.

Stock-based Compensation (Tables)

9 Months Ended

Sep. 30, 2023

Stock-Based Compensation Expense by Award Type

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


	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022
Stock options	$	7,275	$	8,663	$	22,868	$	26,755
Restricted stock units		2,843		1,458		8,475		3,970
Employee stock purchase plan		101		124		586		655
	$	10,219	$	10,245	$	31,929	$	31,380

Stock-Based Compensation Expense

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


	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022
Research and development	$	5,131	$	5,351	$	16,670	$	16,426
General and administrative		5,088		4,894		15,259		14,954
	$	10,219	$	10,245	$	31,929	$	31,380

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, 2022		613		$	35.41
Granted		1,029		$	22.07
Vested		(179	)	$	35.18
Forfeited		(69	)	$	27.16
Unvested balance at September 30, 2023		1,394		$	26.00

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, 2022		7,668		$	34.43		6.5	$	15,783
Granted		1,699		$	21.93
Exercised		(171	)	$	7.66
Cancelled or forfeited		(340	)	$	35.42
Outstanding at September 30, 2023		8,856		$	32.51		6.4	$	6,443
Exercisable at September 30, 2023		6,011		$	34.48		5.4	$	6,443
Vested and expected to vest at September 30, 2023		8,856		$	32.51		6.4	$	6,443

Summary of Significant Accounting Policies (Policies)

9 Months Ended

Sep. 30, 2023

Accounting Policies [Abstract]

Basis of Presentation and Principles of Consolidation

Use of Estimates

Reclassifications

Restricted Cash


	As of September 30,
	2023		2022
Cash and cash equivalents	$	53,045	$	118,544
Restricted cash		2,255		2,030
Total cash and cash equivalents and restricted cash	$	55,300	$	120,574

Accounts Receivable

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.

Net Loss Per Share

Summary of Significant Accounting Policies (Tables)

9 Months Ended

Sep. 30, 2023

Accounting Policies [Abstract]

Summary of Reconciliation of Cash and Cash Equivalents and Restricted Cash

The following table provides a reconciliation of cash and cash equivalents and restricted cash as reported on the consolidated balance sheets to the total of these amounts as reported at the end of the period in the consolidated statements of cash flows (in thousands):


	As of September 30,
	2023		2022
Cash and cash equivalents	$	53,045	$	118,544
Restricted cash		2,255		2,030
Total cash and cash equivalents and restricted cash	$	55,300	$	120,574

Liability Related to Sale of Future Royalties

9 Months Ended

Sep. 30, 2023

6. Liability Related to Sale of Future Royalties

In December 2020, the Company entered into a royalty purchase agreement (the Royalty Purchase Agreement) with entities managed by Healthcare Royalty Management, LLC (collectively, HCR). Under the Royalty Purchase Agreement, HCR purchased the Company’s rights to a capped amount of Zolgensma royalty payments under the Company’s license agreement (the Novartis License) with Novartis Gene Therapies, Inc. (formerly AveXis, Inc.) (Novartis Gene Therapies), including $4.0 million of royalty payments received by the Company in the fourth quarter of 2020 (the Pledged Royalties). In consideration for these rights, HCR paid the Company $200.0 million (the Purchase Price), less $4.0 million representing the payment of the Pledged Royalties to HCR. Beginning upon the effective date of the Royalty Purchase Agreement, Zolgensma royalty payments, up to a specified threshold, shall be paid to HCR, net of upstream royalties payable by the Company to certain licensors in accordance with existing license agreements.

Pursuant to the Royalty Purchase Agreement, the total amount of royalty payments to be received by HCR is subject to an increasing cap (the Cap Amount) equal to (i) $260.0 million applicable for the period from the effective date of the Royalty Purchase Agreement through November 7, 2024, and (ii) $300.0 million applicable for the period from November 8, 2024 through the effective date of termination of the Novartis License. If, on or prior to the defined dates for each Cap Amount, the total amount of royalty payments received by HCR equals or exceeds the Cap Amount applicable to such date, the Royalty Purchase Agreement will automatically terminate and all rights to the Zolgensma royalty payments will revert back to the Company. The Company has no obligation to repay any amounts to HCR if total future Zolgensma royalty payments are not sufficient to achieve the applicable Cap Amount prior to the termination of the Novartis License.

The Company has a call option to repurchase its rights to the purchased royalties from HCR for a repurchase price equal to, as of the option exercise date, $300.0 million minus the total amount of royalty payments received by HCR; provided, however, that with respect to a call option exercised on or before November 7, 2024, in the event that the then applicable Cap Amount minus the total amount of royalty payments received by HCR is less than $1.0 million, the repurchase price shall equal such difference.

The proceeds received from HCR of $196.0 million were recorded as a liability, net of transaction costs of $3.5 million, which is amortized over the estimated life of the arrangement using the effective interest method. In order to determine the amortization of the liability, the Company is required to estimate the total amount of future royalty payments to be received by HCR, subject to the Cap Amount, over the life of the arrangement. The total amount of royalty payments received by HCR under the Royalty Purchase Agreement, less the net proceeds received by the Company of $192.5 million, is recorded as interest expense over the life of the arrangement using the effective interest method. Due to its continuing involvement in the Novartis License, the Company continues to recognize royalty revenue on net sales of Zolgensma and records the royalty payments to HCR as a reduction of the liability when paid. As such payments are made to HCR, the balance of the liability will be effectively repaid over the life of the Royalty Purchase Agreement.

The Company estimates the effective interest rate used to record interest expense under the Royalty Purchase Agreement based on its estimate of future royalty payments to be received by HCR. As of September 30, 2023, the estimated effective interest rate under the Royalty Purchase Agreement was 5.2%. Over the life of the arrangement, the actual effective interest rate will be affected by the amount and timing of the royalty payments received by HCR and changes in the Company’s forecasted royalties. At each reporting date, the Company reassesses its estimate of total future royalty payments to be received by HCR at the applicable Cap Amount, and prospectively adjusts the effective interest rate and amortization of the liability, as necessary.

The following table presents the changes in the liability related to the sale of future royalties under the Royalty Purchase Agreement with HCR (in thousands):


	Liability Related to
	Sale of Future Royalties
Balance at December 31, 2022	$	137,606
Zolgensma royalties paid to HCR		(36,614	)
Interest expense recognized		4,854
Balance at September 30, 2023		105,846
Current portion of liability related to sale of future royalties		(52,750	)
Non-current portion of liability related to sale of future royalties	$	53,096

Pay vs Performance Disclosure - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Pay vs Performance Disclosure
Net Income (Loss)	$ (61,868)	$ (75,484)	$ (200,605)	$ (220,386)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(g)(1)(ii))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 323
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481687/323-10-50-3

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 825
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 28
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482907/825-10-50-28

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482765/220-10-50-6

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-3

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (b)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 65
-Paragraph 1
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480175/815-40-65-1

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-8

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-9

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-11

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-11

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-4

Reference 13: http://www.xbrl.org/2003/role/exampleRef
-Topic 946
-SubTopic 830
-Name Accounting Standards Codification
-Section 55
-Paragraph 10
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480167/946-830-55-10

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section 45
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483581/946-220-45-7

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
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Reference 30: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

License and Collaboration Agreements - Summary of Accounts Recerivable, Net (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Current accounts receivable:
Billed to customers	$ 92	$ 280
Unbilled Zolgensma royalties	27,311	27,027
Other unbilled	640	775
Current accounts receivable, net	28,043	28,082
Non-current accounts receivable:
Due from Abeona, net of present value discount	$ 4,474	$ 4,152
Other Receivable, after Allowance for Credit Loss, Noncurrent, Related and Nonrelated Party Status [Extensible Enumeration]	Related Party [Member]	Related Party [Member]
Other unbilled	$ 1,078	$ 1,504
Allowance for credit losses	(4,474)	(4,152)
Non-current accounts receivable, net	1,078	1,504
Total accounts receivable, net	$ 29,121	$ 29,586

Property and Equipment Net - Schedule of Property and Equipment (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Property Plant And Equipment [Line Items]
Total property and equipment	$ 189,908	$ 183,073
Accumulated depreciation and amortization	(54,374)	(41,388)
Property and equipment, net	135,534	141,685
Laboratory and Manufacturing Equipment [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	75,214	71,801
Computer Equipment and Software [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	5,748	4,910
Furniture and Fixtures [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	7,078	6,965
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	$ 101,868	$ 99,397

Marketable Securities - Summary of Fair Values and Unrealized Losses of Marketable Securities Held by the Company in an Unrealized Loss Position for Less Than 12 months and 12 Months or Greater (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Schedule Of Available For Sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 64,892	$ 202,689
Less than 12 Months, Unrealized Losses	(201)	(6,024)
12 Months or Greater, Fair Value	239,366	263,824
12 Months or Greater, Unrealized Losses	(6,352)	(8,519)
Total, Fair Value	304,258	466,513
Total, Unrealized Losses	(6,553)	(14,543)
U.S. Government and Agency Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than 12 Months, Fair Value	23,688	91,498
Less than 12 Months, Unrealized Losses	(68)	(2,014)
12 Months or Greater, Fair Value	61,885	38,495
12 Months or Greater, Unrealized Losses	(1,977)	(1,478)
Total, Fair Value	85,573	129,993
Total, Unrealized Losses	(2,045)	(3,492)
Certificates of Deposit [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than 12 Months, Fair Value	2,411	4,484
Less than 12 Months, Unrealized Losses	(24)	(144)
12 Months or Greater, Fair Value	3,753	2,087
12 Months or Greater, Unrealized Losses	(140)	(104)
Total, Fair Value	6,164	6,571
Total, Unrealized Losses	(164)	(248)
Corporate Bonds [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than 12 Months, Fair Value	38,793	106,707
Less than 12 Months, Unrealized Losses	(109)	(3,866)
12 Months or Greater, Fair Value	173,728	223,242
12 Months or Greater, Unrealized Losses	(4,235)	(6,937)
Total, Fair Value	212,521	329,949
Total, Unrealized Losses	$ (4,344)	$ (10,803)

License and Collaboration Agreements - Additional Information (Detail)	1 Months Ended	3 Months Ended		9 Months Ended
	Nov. 30, 2021 USD ($)	Sep. 30, 2023 USD ($) ProductCandidate	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) ProductCandidate	Sep. 30, 2022 USD ($)	Jun. 30, 2023 USD ($)	Dec. 31, 2022 USD ($)	Jun. 30, 2022 USD ($)	Dec. 31, 2021 USD ($)
License Revenue [Line Items]
Milestone payment upon commencement of clinical trials in humans				$ 533,800,000
Milestone payment upon submission of regulatory approval filings				17,000,000
Milestone payment upon approval of commercial products by regulatory agencies				123,000,000
Milestone payment upon achievement of specified sales targets for licensed products				875,000,000
Deferred revenue, current and non-current		$ 442,000	$ 5,903,000	442,000	$ 5,903,000	$ 448,000	$ 1,829,000	$ 6,636,000	$ 3,333,000
Contract assets		2,000,000		2,000,000		$ 2,000,000	0		$ 1,074,000
Aggregate transaction price of license agreements				1,600,000
Revenue recognized upon achievement of development milestones		0	0	2,000,000	0
Provision for credit losses		0	0	0	0
Accounts receivable, current		28,043,000		28,043,000			28,082,000
Accounts receivable, net		1,078,000		1,078,000			1,504,000
Other Current Assets [Member] \| Related Party [Member]
License Revenue [Line Items]
Due from related parties, current		18,684,000		18,684,000			6,294,000
Abb Vie Collaboration And License Agreement
License Revenue [Line Items]
Up-front fee paid	$ 370,000,000.0
Milestone fee payments upon achievement of various development and commercialization	1,380,000,000
Transaction price of license		370,000,000.0		370,000,000.0			370,000,000.0
Change in transaction price		0	0	0	0
Abb Vie Collaboration And License Agreement \| Other Current Assets [Member] \| Related Party [Member]
License Revenue [Line Items]
Due from related parties, current		18,700,000		18,700,000			6,200,000
Novartis License Agreement [Member] \| Novartis Gene Therapies [Member]
License Revenue [Line Items]
Accounts receivable		27,500,000		27,500,000			27,300,000
November Two Thousand Eighteen License Agreement \| Abeona Therapeutics Incorporation \| Contract Termination
License Revenue [Line Items]
Settlement agreement payable				30,000,000.0
November Two Thousand Twenty One License Agreement \| Abeona Therapeutics Incorporation \| Contract Termination
License Revenue [Line Items]
Settlement agreement payable				20,000,000.0
November Two Thousand Twenty Two License Agreement \| Abeona Therapeutics Incorporation \| Contract Termination
License Revenue [Line Items]
Settlement agreement payable				5,000,000.0
November Two Thousand Twenty Four License Agreement \| Abeona Therapeutics Incorporation \| Contract Termination
License Revenue [Line Items]
Settlement agreement payable				5,000,000.0
Settlement Agreement \| Abeona Therapeutics Incorporation
License Revenue [Line Items]
Accounts receivable		4,500,000		4,500,000
Accounts receivable, Non-current		4,500,000		4,500,000			4,200,000
Due from related parties		$ 5,000,000.0		$ 5,000,000.0
Other Receivable, after Allowance for Credit Loss, Related and Nonrelated Party Status [Extensible Enumeration]		Related Party [Member]		Related Party [Member]
Allowance for credit losses		$ 4,500,000		$ 4,500,000			4,200,000
Provision for credit losses		0	$ 0	0	$ 0
Sales Based Milestones \| Abb Vie Collaboration And License Agreement
License Revenue [Line Items]
Milestone fee payments upon achievement of various development and commercialization	820,000,000.0
Transaction price of license		820,000,000.0		820,000,000.0			820,000,000.0
Development Milestone \| Abb Vie Collaboration And License Agreement
License Revenue [Line Items]
Milestone fee payments upon achievement of various development and commercialization	$ 562,500,000
Transaction price of license		$ 562,500,000		562,500,000			$ 562,500,000
Maximum [Member]
License Revenue [Line Items]
Aggregate milestone payment for all the targets				$ 1,550,000,000
Aggregate transaction price of license agreements, expected satisfaction period				3 years
Minimum [Member]
License Revenue [Line Items]
Aggregate transaction price of license agreements, expected satisfaction period				2 years
N A V Technology Platform [Member]
License Revenue [Line Items]
Number of commercial product candidates \| ProductCandidate		1		1
HCR [Member] \| Novartis License Agreement [Member] \| Novartis Gene Therapies [Member]
License Revenue [Line Items]
Accounts receivable, current		$ 14,900,000		$ 14,900,000

License and Collaboration Agreements - Schedule Of License and Royalty Revenue (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
License Revenue [Line Items]
Other license and royalty revenue	$ 550	$ 1,307	$ 4,575	$ 6,249
Total license and royalty revenue	28,914	26,512	68,029	81,379
Zolgensma Royalties [Member]
License Revenue [Line Items]
Zolgensma royalties	$ 28,364	$ 25,205	$ 63,454	$ 75,130

- Definition

Amount, including tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value-added and excise.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 924
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 11.L)
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-URI https://asc.fasb.org//1943274/2147479941/924-10-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
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-URI https://asc.fasb.org//1943274/2147479806/606-10-50-5

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org//1943274/2147482810/280-10-50-30

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org//1943274/2147482810/280-10-50-42

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
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Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-4

+ Details

Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Current assets
Cash and cash equivalents	$ 53,045	$ 96,952
Marketable securities	248,842	267,690
Accounts receivable	28,043	28,082
Prepaid expenses	12,561	13,900
Other current assets	23,347	9,352
Total current assets	365,838	415,976
Marketable securities	62,639	200,560
Accounts receivable, net	1,078	1,504
Property and equipment, net	135,534	141,685
Operating lease right-of-use assets	61,773	65,116
Restricted cash	2,255	2,030
Other assets	4,669	6,397
Total assets	633,786	833,268
Current liabilities
Accounts payable	21,859	27,213
Accrued expenses and other current liabilities	45,656	46,794
Deferred revenue	442	1,829
Operating lease liabilities	6,639	5,997
Liability related to sale of future royalties	52,750	48,601
Total current liabilities	127,346	130,434
Operating lease liabilities	84,058	88,802
Liability related to sale of future royalties	53,096	89,005
Other liabilities	6,186	8,832
Total liabilities	270,686	317,073
Stockholders’ equity
Preferred stock; $0.0001 par value; 10,000 shares authorized, no shares issued and outstanding at September 30, 2023 and December 31, 2022
Common stock; $0.0001 par value; 100,000 shares authorized at September 30, 2023 and December 31, 2022; 43,621 and 43,299 shares issued and outstanding at September 30, 2023 and December 31, 2022, respectively	4	4
Additional paid-in capital	1,012,667	973,145
Accumulated other comprehensive loss	(7,413)	(15,401)
Accumulated deficit	(642,158)	(441,553)
Total stockholders’ equity	363,100	516,195
Total liabilities and stockholders’ equity	$ 633,786	$ 833,268

Fair Value of Financial Instruments - Additional Information (Detail) € in Millions	1 Months Ended		3 Months Ended			9 Months Ended
	Jul. 31, 2023 EUR (€)	Jul. 31, 2023 USD ($)	Sep. 30, 2023 EUR (€)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2023 EUR (€)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Non-marketable equity securities				$ 0			$ 0		$ 0
Re measurements or impairment losses on non-marketable equity securities				0	$ 0		0	$ 0
Investment income				4,660,000	$ 1,497,000		8,953,000	$ 3,357,000
Uni Qure N V
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Proceeds from acquiring business	€ 5.3	$ 6,100,000
Investment income				$ 2,200,000			2,200,000
Revenue recognition, milestone method, revenue recognized \| €			€ 1.9			€ 37.1
Revenue recognition, milestone method, revenue recognized not yet paid or achieved						€ 35.3	$ 37,300,000

Related Party Transactions

9 Months Ended

Sep. 30, 2023

Related Party Transactions

12. Related Party Transactions

FOXKISER LLP

From 2016 until June 2022, the Company was a party to professional services agreements with FOXKISER LLP (FOXKISER), an affiliate of certain stockholders of the Company and an affiliate of a member of the Company’s Board of Directors, pursuant to which the Company paid a fixed monthly fee in consideration for certain strategic services provided by FOXKISER. The agreement with FOXKISER was terminated effective June 2022. Expenses incurred under the agreement with FOXKISER were zero and $2.4 million for the three and nine months ended September 30, 2022, respectively, and were recorded as research and development expenses in the consolidated statements of operations and comprehensive loss. The Company did not record any expenses under the agreement with FOXKISER during the three and nine months ended September 30, 2023.

- Definition

The entire disclosure for related party transactions. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org//1943274/2147480990/946-20-50-5

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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-Subparagraph (e)
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-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)
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-URI https://asc.fasb.org//1943274/2147483326/850-10-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
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-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(g)(3))
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(c))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(e))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//850/tableOfContent

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
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-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-6

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-1

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-1

+ Details

Supplemental Disclosures - Schedules of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Payables and Accruals [Abstract]
Accrued sublicense fees and royalties	$ 15,022	$ 15,768
Accrued personnel costs	14,864	18,071
Accrued external research and development expenses	11,681	9,216
Accrued external general and administrative expenses	2,759	2,187
Accrued purchases of property and equipment	469	806
Other accrued expenses and current liabilities	861	746
Accrued expenses and other current liabilities	$ 45,656	$ 46,794

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, 2021	$ 764,298	$ 4	$ 928,095	$ (2,569)	$ (161,232)
Balances (Shares) at Dec. 31, 2021		42,831
Vesting of restricted stock units, net of tax	(284)		(284)
Vesting of restricted stock units, net of tax, shares		57
Exercise of stock options, net of tax	2,761		2,761
Exercise of stock options, net of tax, shares		329
Issuance of common stock under employee stock purchase plan	1,742		1,742
Issuance of common stock under employee stock purchase plan, shares		75
Stock-based compensation expense	31,380		31,380
Unrealized gain (loss) on available-for-sale securities, net	(15,687)			(15,687)
Net loss	(220,386)				(220,386)
Balances at Sep. 30, 2022	563,824	$ 4	963,694	(18,256)	(381,618)
Balances (Shares) at Sep. 30, 2022		43,292
Balances at Jun. 30, 2022	630,519	$ 4	951,412	(14,763)	(306,134)
Balances (Shares) at Jun. 30, 2022		43,171
Vesting of restricted stock units, net of tax, shares		2
Exercise of stock options, net of tax	917		917
Exercise of stock options, net of tax, shares		66
Issuance of common stock under employee stock purchase plan	1,120		1,120
Issuance of common stock under employee stock purchase plan, shares		53
Stock-based compensation expense	10,245		10,245
Unrealized gain (loss) on available-for-sale securities, net	(3,493)			(3,493)
Net loss	(75,484)				(75,484)
Balances at Sep. 30, 2022	563,824	$ 4	963,694	(18,256)	(381,618)
Balances (Shares) at Sep. 30, 2022		43,292
Balances at Dec. 31, 2022	516,195	$ 4	973,145	(15,401)	(441,553)
Balances (Shares) at Dec. 31, 2022		43,299
Vesting of restricted stock units, net of tax	(419)		(419)
Vesting of restricted stock units, net of tax, shares		161
Exercise of stock options, net of tax	1,312		1,312
Exercise of stock options, net of tax, shares		171
Issuance of common stock under employee stock purchase plan	1,826		1,826
Issuance of common stock under employee stock purchase plan, shares		103
Issuance of common stock upon private placement	4,874		4,874
Issuance of common stock upon private placement, shares		257
Stock-based compensation expense	31,929		31,929
Unrealized gain (loss) on available-for-sale securities, net	7,988			7,988
Net loss	(200,605)				(200,605)
Balances at Sep. 30, 2023	363,100	$ 4	1,012,667	(7,413)	(642,158)
Balances (Shares) at Sep. 30, 2023		43,991
Balances at Jun. 30, 2023	405,855	$ 4	996,239	(10,098)	(580,290)
Balances (Shares) at Jun. 30, 2023		43,621
Vesting of restricted stock units, net of tax, shares		34
Exercise of stock options, net of tax	92		92
Exercise of stock options, net of tax, shares		6
Issuance of common stock under employee stock purchase plan	1,243		1,243
Issuance of common stock under employee stock purchase plan, shares		73
Issuance of common stock upon private placement	4,874		4,874
Issuance of common stock upon private placement, shares		257
Stock-based compensation expense	10,219		10,219
Unrealized gain (loss) on available-for-sale securities, net	2,685			2,685
Net loss	(61,868)				(61,868)
Balances at Sep. 30, 2023	$ 363,100	$ 4	$ 1,012,667	$ (7,413)	$ (642,158)
Balances (Shares) at Sep. 30, 2023		43,991

Income Taxes

9 Months Ended

Sep. 30, 2023

Income Tax Disclosure [Abstract]

Income Taxes

11. Income Taxes

The Company evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets as of September 30, 2023 and December 31, 2022. Based on the Company’s history of operating losses, and other relevant facts and circumstances, the Company concluded that it was more likely than not that the benefit of its deferred tax assets will not be realized. Accordingly, the Company provided a full valuation allowance for its net deferred tax assets as of September 30, 2023 and December 31, 2022.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//740/tableOfContent

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-14

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 21
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-21

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 270
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482526/740-270-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 17
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-17

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 6.I.5.Q1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 11.C)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-2

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482603/740-30-50-2

+ Details

Supplemental Disclosures - Schedule of Other Current Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Other Current Assets [Line Items]
Other current assets	$ 23,347	$ 9,352
Other Current Assets [Member]
Other Current Assets [Line Items]
License revenue contract assets	2,000
Accrued Interest on Investments	1,673	2,210
Other	990	848
Other current assets	23,347	9,352
Other Current Assets [Member] \| Related Party [Member]
Other Current Assets [Line Items]
Net cost reimbursement due from collaborators	$ 18,684	$ 6,294

License and Collaboration Agreements - Summary of Changes in Balances of Receivables, Contract Assets and Deferred Revenue (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Accounts receivable, net, current and non-current:
Balance, beginning of period	$ 22,523,000	$ 39,534,000	$ 29,586,000	$ 34,701,000
Balance, end of period	29,121,000	34,352,000	29,121,000	34,352,000
Contract assets:
Balance, beginning of period	2,000,000		0	1,074,000
Balance, end of period	2,000,000		2,000,000
Deferred revenue, current and non-current:
Balance, beginning of period	448,000	6,636,000	1,829,000	3,333,000
Balance, end of period	442,000	5,903,000	442,000	5,903,000
Revenue recognized during the period from:
Amounts included in deferred revenue at beginning of period	28,000	1,343,000	1,409,000
Performance obligations satisfied in previous periods	$ 28,365,000	$ 25,169,000	$ 65,405,000	$ 75,130,000

Net Loss Per Share

9 Months Ended

Sep. 30, 2023

Earnings Per Share [Abstract]

Net Loss Per Share

13. Net Loss Per Share

Since the Company incurred net losses for the three and nine months ended September 30, 2023 and 2022, common stock equivalents were excluded from the calculation of diluted net loss per share for such periods as their effect would be anti-dilutive. Accordingly, basic and diluted net loss per share were the same for such periods. The following potentially dilutive common stock equivalents outstanding at the end of the period were excluded from the computations of weighted-average diluted common shares for the periods indicated as their effects would be anti-dilutive (in thousands):


	Three and Nine Months Ended September 30,
	2023		2022
Stock options issued and outstanding		8,856		7,774
Unvested restricted stock units outstanding		1,394		617
Employee stock purchase plan		36		26
		10,286		8,417

Property and Equipment, Net (Tables)

9 Months Ended

Sep. 30, 2023

Property, Plant and Equipment [Abstract]

Schedule of Property and Equipment

Property and equipment, net consists of the following (in thousands):


	September 30, 2023			December 31, 2022
Laboratory and manufacturing equipment	$	75,214		$	71,801
Computer equipment and software		5,748			4,910
Furniture and fixtures		7,078			6,965
Leasehold improvements		101,868			99,397
Total property and equipment		189,908			183,073
Accumulated depreciation and amortization		(54,374	)		(41,388	)
Property and equipment, net	$	135,534		$	141,685

Stock-based Compensation - Summary of Unvested RSUs Activity Under 2015 Plan (Detail) - Restricted Stock Units (RSUs)	9 Months Ended
	Sep. 30, 2023 $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unvested balance at December 31, 2022 \| shares	613,000
Shares, Granted \| shares	1,029,000
Vested \| shares	(179,000)
Forfeited \| shares	(69,000)
Unvested balance at March 31, 2023 \| shares	1,394,000
Weighted-average Grant Date Fair Value, Unvested Beginning Balance \| $ / shares	$ 35.41
Weighted-average Grant Date Fair Value, Granted \| $ / shares	22.07
Weighted-average Grant Date Fair Value, Vested \| $ / shares	35.18
Weighted-average Grant Date Fair Value, Forfeited \| $ / shares	27.16
Weighted-average Grant Date Fair Value, Unvested Ending Balance \| $ / shares	$ 26

Stock-based Compensation - Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 10,219	$ 10,245	$ 31,929	$ 31,380
Research and Development Expense [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	5,131	5,351	16,670	16,426
General and Administrative Expense [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 5,088	$ 4,894	$ 15,259	$ 14,954

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

+ Details

License and Collaboration Agreements

9 Months Ended

Sep. 30, 2023

Organization, Consolidation and Presentation of Financial Statements [Abstract]

License and Collaboration Agreements

9. License and Collaboration Agreements

License and Royalty Revenue

As of September 30, 2023, the Company’s NAV Technology Platform was being applied by NAV Technology Licensees in one commercially available product, Zolgensma, and in the development of a number of other licensed products. Additionally, the Company has licensed intellectual property rights to collaborators for the joint development of certain product candidates. Consideration to the Company under its license agreements may include: (i) up-front and annual fees, (ii) milestone payments based on the achievement of certain development and sales-based milestones, (iii) sublicense fees, (iv) royalties on sales of licensed products and (v) other consideration payable upon optional goods and services purchased by licensees. 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.

License and royalty revenue consisted of the following (in thousands):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022
Zolgensma royalties	$	28,364	$	25,205	$	63,454	$	75,130
Other license and royalty revenue		550		1,307		4,575		6,249
Total license and royalty revenue	$	28,914	$	26,512	$	68,029	$	81,379

Outstanding development milestone payments are evaluated each reporting period and are only included in the transaction price of each license and recognized as license revenue to the extent the milestones are considered probable of achievement. Sales-based milestones are excluded from the transaction price of each license agreement and recognized as royalty revenue in the period of achievement. As of September 30, 2023, 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 $1.55 billion, including (i) $533.8 million upon the commencement of various stages of clinical trials, (ii) $17.0 million upon the submission of regulatory approval filings, (iii) $123.0 million upon the approval of commercial products by regulatory agencies and (iv) $875.0 million upon the achievement of specified sales targets for licensed products, including milestones payable upon the first commercial sales of 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 these milestones 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.

Changes in Accounts Receivable, Contract Assets and Deferred Revenue


	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022
Accounts receivable, net, current and non-current:
Beginning of period	$	22,523	$	39,534	$	29,586	$	34,701
End of period	$	29,121	$	34,352	$	29,121	$	34,352

Contract assets:
Beginning of period	$	2,000	$	—	$	—	$	1,074
End of period	$	2,000	$	—	$	2,000	$	—

Deferred revenue, current and non-current:
Beginning of period	$	448	$	6,636	$	1,829	$	3,333
End of period	$	442	$	5,903	$	442	$	5,903

Revenue recognized during the period from:
Amounts included in deferred revenue at beginning of period	$	28	$	1,343	$	1,409	$	—
Performance obligations satisfied in previous periods	$	28,365	$	25,169	$	65,405	$	75,130

Contract assets as of September 30, 2023 are included in other current assets on the consolidated balance sheet. The Company did not record any contract assets as of December 31, 2022.

As of September 30, 2023, the Company had recorded deferred revenue of $0.4 million which represents consideration received or unconditionally due from licensees for performance obligations that have not yet been satisfied by the Company. Unsatisfied performance obligations as of September 30, 2023 consisted of research and development services to be performed by the Company related to licensed products, which will be satisfied as the research and development services are performed. As of September 30, 2023, the aggregate transaction price of the Company’s license agreements allocated to performance obligations not yet satisfied, or partially satisfied, was $1.6 million, which is expected to be satisfied over a period of approximately two to three years.

Revenue recognized from performance obligations satisfied in previous periods, as presented in the table above, was primarily attributable to Zolgensma royalties and changes in the transaction prices of the Company’s license agreements. Changes in transaction prices were primarily attributable to development milestones achieved or deemed probable of achievement during the periods which were previously not considered probable of achievement, resulting in a cumulative catch-up adjustment to revenue. Revenue recognized during the nine months ended September 30, 2023 resulting from performance obligations satisfied in previous periods included $2.0 million in cumulative catch-up adjustments for changes in the probability of achievement of development milestones. There were no cumulative catch-up adjustments to revenue for changes in the probability of achievement of development milestones during the three months ended September 30, 2023 or during the three and nine months ended September 30, 2022.

Accounts Receivable, Contract Assets and the Allowance for Credit Losses

Accounts receivable, net consisted of the following (in thousands):


	September 30, 2023			December 31, 2022
Current accounts receivable:
Billed to customers	$	92		$	280
Unbilled Zolgensma royalties		27,311			27,027
Other unbilled		640			775
Allowance for credit losses		—			—
Current accounts receivable, net		28,043			28,082
Non-current accounts receivable:
Due from Abeona, net of present value discount		4,474			4,152
Other unbilled		1,078			1,504
Allowance for credit losses		(4,474	)		(4,152	)
Non-current accounts receivable, net		1,078			1,504
Total accounts receivable, net	$	29,121		$	29,586

The following table presents the changes in the allowance for credit losses related to accounts receivable and contract assets for the nine months ended September 30, 2023 (in thousands):


	Allowance for Credit Losses
	Accounts Receivable		Contract Assets
Balance at December 31, 2022	$	4,152	$	—
Changes in present value discount of receivables		322		—
Balance at September 30, 2023	$	4,474	$	—

The Company’s allowance for credit losses as of September 30, 2023 and December 31, 2022 was related solely to accounts receivable from Abeona Therapeutics Inc. (Abeona). Please refer to the section below, "Settlement Agreement with Abeona Therapeutics", for further information regarding amounts due from Abeona and the associated allowance for credit losses. The Company did not record a provision for credit losses for the three and nine months ended September 30, 2023 and 2022.

Zolgensma License with Novartis Gene Therapies

In March 2014, the Company entered into an exclusive license agreement (as amended, the Novartis License) with Novartis Gene Therapies (formerly AveXis, Inc.). Under the Novartis License, the Company granted Novartis Gene Therapies an exclusive, worldwide commercial license, with rights to sublicense, to the NAV Technology Platform, as well as other certain rights, for the treatment of spinal muscular atrophy (SMA) in humans by in vivo gene therapy. In 2019, Novartis Gene Therapies launched commercial sales of Zolgensma, a licensed product under the Novartis License. In accordance with the Novartis License, the Company receives royalties on net sales of Zolgensma.

The Company recognized the following amounts under the Novartis License (in thousands):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022
Zolgensma royalties	$	28,364	$	25,205	$	63,454	$	75,130
Other license revenue		—		—		—		31
Total license and royalty revenue	$	28,364	$	25,205	$	63,454	$	75,161

Interest income from licensing	$	7	$	8	$	22	$	84

As of September 30, 2023 and December 31, 2022, the Company had recorded total accounts receivable of $27.5 million and $27.3 million, respectively, from Novartis Gene Therapies under the Novartis License, which consisted primarily of Zolgensma royalties receivable. The Zolgensma royalties receivable recorded as of September 30, 2023 included $14.9 million expected to be paid to HCR in accordance with the Royalty Purchase Agreement discussed in Note 6. The Company recognizes royalty revenue from net sales of Zolgensma in the period in which the underlying products are sold by Novartis Gene Therapies, 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. Estimated royalties are reconciled to actual amounts reported in subsequent periods, and any differences are recognized as an adjustment to royalty revenue in the period the royalties are reported.

Settlement Agreement with Abeona Therapeutics

In November 2021, the Company entered into a settlement agreement and mutual release with Abeona (the Settlement Agreement) related to claims associated with a license agreement between the parties which was terminated in May 2020. The Settlement Agreement resolved all arbitration and legal proceedings and mutually released each party from any and all claims under the terminated license agreement. Pursuant to the Settlement Agreement, Abeona will pay the Company a total of $30.0 million as follows: (i) $20.0 million which was paid in November 2021, (ii) $5.0 which was paid in November 2022, and (iii) $5.0 million payable on the earlier of the third anniversary of the Settlement Agreement in November 2024 or the closing of a specified type of transaction by Abeona.

As of September 30, 2023 and December 31, 2022, the Company had recorded gross, non-current accounts receivable of $4.5 million and $4.2 million, respectively, from Abeona under the Settlement Agreement. The gross accounts receivable of $4.5 million as of September 30, 2023 consisted of the $5.0 million payment due by November 2024, net of discount to present value. While the Company anticipates taking appropriate measures to enforce the full collection of all amounts due from Abeona under the Settlement Agreement, the Company assessed the collectability of the accounts receivable from Abeona as it relates to credit risk. In performing this assessment, the Company evaluated Abeona’s credit profile and financial condition, as well its expectations regarding Abeona’s future cash flows and ability to satisfy the contractual obligations of the Settlement Agreement. As a result of its analysis, the Company recorded an allowance for credit losses of $4.5 million and $4.2 million as of September 30, 2023 and December 31, 2022, respectively, related to the non-current accounts receivable due from Abeona. No provision for credit losses was recorded for the three and nine months ended September 30, 2023 and 2022 related to the receivable from Abeona. The present value discount of the non-current accounts receivable from Abeona is accreted as interest income from licensing through the contractual due date using the effective interest method. The Company has elected to record increases in the allowance for credit losses associated with the accretion of the present value discount of the receivable as a reduction of the associated interest income, resulting in no interest income recognized during the periods related to the accretion of the present value discount on the non-current receivable from Abeona.

Collaboration Agreements

AbbVie Collaboration and License Agreement

Effective in November 2021, the Company entered into a collaboration and license agreement with AbbVie Global Enterprises Ltd. (AbbVie), a subsidiary of AbbVie Inc., to jointly develop and commercialize ABBV-RGX-314, the Company’s product candidate for the treatment of wet age-related macular degeneration (wet AMD), diabetic retinopathy (DR) and other chronic retinal diseases (the AbbVie Collaboration Agreement).

Pursuant to the AbbVie Collaboration Agreement, the Company granted AbbVie a co-exclusive license to develop and commercialize ABBV-RGX-314 in the United States and an exclusive license to develop and commercialize ABBV-RGX-314 outside the United States. The Company and AbbVie will collaborate to develop ABBV-RGX-314 in the United States, and AbbVie will be responsible for the development of ABBV-RGX-314 in specified markets outside the United States. Through December 31, 2022, the Company was responsible for the development expenses related to certain ongoing clinical trials of ABBV-RGX-314 and the parties shared the additional development expenses related to ABBV-RGX-314. Beginning on January 1, 2023, AbbVie became responsible for the majority of all ABBV-RGX-314 development expenses.

The Company will lead the manufacturing of ABBV-RGX-314 for clinical development and U.S. commercial supply, and AbbVie will lead the manufacturing of ABBV-RGX-314 for commercial supply outside the United States. Manufacturing expenses will be allocated between the parties in accordance with the terms of the AbbVie Collaboration Agreement and supply agreements determined in accordance with the agreement. If requested by AbbVie, the Company will manufacture up to a specified portion of ABBV-RGX-314 for commercial supply outside the United States at a price specified in the agreement. AbbVie will lead the commercialization of ABBV-RGX-314 globally, and the Company will participate in U.S. commercialization efforts as provided under a commercialization plan determined in accordance with the agreement. The Company and AbbVie will share equally in the net profits and net losses associated with the commercialization of ABBV-RGX-314 in the United States. Outside the United States, AbbVie will be responsible, at its sole cost, for the commercialization of ABBV-RGX-314.

In consideration for the rights granted under the AbbVie Collaboration Agreement, AbbVie paid the Company an up-front fee of $370.0 million upon the effective date of the agreement in November 2021 and is required to pay to the Company up to $1.38 billion upon the achievement of specified development and sales-based milestones, of which $562.5 million are based on development milestones and $820.0 million are sales-based milestones. AbbVie is also required to pay to the Company tiered royalties on net sales of ABBV-RGX-314 outside the United States at percentages in the mid-teens to low twenties, subject to specified offsets and reductions.

The Company applied the requirements of ASC 606, Revenue from Contracts with Customers (Topic 606) to the AbbVie Collaboration Agreement for the units of account in which AbbVie was deemed to be a customer. The Company determined that there is only one material performance obligation under the agreement for the delivery of the intellectual property license to develop and commercialize ABBV-RGX-314 globally. The intellectual property licensed to AbbVie includes the rights to certain patents, data, know-how and other rights developed and owned by the Company, as well as other intellectual property rights exclusively licensed by the Company from various third parties. As of September 30, 2023 and December 31, 2022, the transaction price of the AbbVie Collaboration Agreement was $370.0 million, which consisted solely of the up-front payment received from AbbVie in November 2021. The $370.0 million transaction price was fully recognized as revenue upon the delivery of the license to AbbVie in November 2021. Variable consideration under the AbbVie Collaboration Agreement, which has been excluded from the transaction price, includes $562.5 million in payments for development milestones that have not yet been achieved and were not considered probable of achievement. Additionally, the transaction price excludes sales-based milestone payments of $820.0 million and royalties on net sales of ABBV-RGX-314 outside the United States. Development milestones will be added to the transaction price and recognized as revenue upon achievement, or if deemed probable of achievement. In accordance with the sale- or usage-based royalty exception under Topic 606, royalties on net sales and sales-based milestones will be recognized as revenue in the period the underlying sales occur or milestones are achieved. There were no changes in the transaction price of the AbbVie Collaboration Agreement, and no revenue was recognized, during the three and nine months ended September 30, 2023 and 2022.

The Company applied the requirements of ASC 808, Collaborative Arrangements (Topic 808) to the AbbVie Collaboration Agreement for the units of account which were deemed to be a collaborative arrangement. Both the Company and AbbVie will perform various activities related to the development, manufacturing and commercialization of ABBV-RGX-314 in the United States. Development costs are shared between the parties in accordance with the terms of the AbbVie Collaboration Agreement, and the parties will share equally in the net profits and losses derived from sales of ABBV-RGX-314 in the United States. The Company accounts for payments to and from AbbVie for the sharing of development and commercialization costs in accordance with its accounting policy for collaborative arrangements. Amounts owed to AbbVie for the Company’s share of development costs or commercialization costs incurred by AbbVie are recorded as research and development expense or general and administrative

expense, respectively, in the period the costs are incurred. Amounts owed to the Company for AbbVie’s share of development costs or commercialization costs incurred by the Company are recorded as a reduction of research and development expense or general and administrative expense, respectively, in the period the costs are incurred. At the end of each reporting period, the Company records a net amount due to or from AbbVie as a result of the cost-sharing arrangement. As of September 30, 2023 and December 31, 2022, the Company had recorded $18.7 million and $6.2 million, respectively, due from AbbVie for net reimbursement of costs incurred for activities performed under AbbVie Collaboration Agreement, which was included in other current assets on the consolidated balance sheets.

The Company recognized the following amounts under the AbbVie Collaboration Agreement (in thousands):


	Three Months Ended September 30,						Nine Months Ended September 30,
	2023			2022			2023			2022
Net cost reimbursement to (from) AbbVie included in:
Research and development expense	$	(19,608	)	$	(4,245	)	$	(56,300	)	$	(12,339	)
General and administrative expense		615			750			1,007			954
Total net cost reimbursement to (from) AbbVie	$	(18,993	)	$	(3,495	)	$	(55,293	)	$	(11,385	)

Marketable Securities (Tables)

9 Months Ended

Sep. 30, 2023

Investments, Debt and Equity Securities [Abstract]

Summary of Company Marketable Securities

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


	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
September 30, 2023
U.S. government and agency securities	$	94,595	$	1	$	(2,045	)	$	92,551
Certificates of deposit		6,573		—		(164	)		6,409
Corporate bonds		216,865		—		(4,344	)		212,521
	$	318,033	$	1	$	(6,553	)	$	311,481


	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
December 31, 2022
U.S. government and agency securities	$	134,485	$	—	$	(3,492	)	$	130,993
Certificates of deposit		7,555		1		(248	)		7,308
Corporate bonds		340,752		—		(10,803	)		329,949
	$	482,792	$	1	$	(14,543	)	$	468,250

Summary of unrealized loss on available-for-sale securities, net, presented in the consolidated statements of operations and comprehensive loss

Unrealized gain (loss) on available-for-sale securities, net, as presented in the consolidated statements of operations and comprehensive loss consisted of the following (in thousands):


	Three Months Ended September 30,					Nine Months Ended September 30,
	2023		2022			2023		2022
Unrealized gain (loss) before reclassifications	$	2,685	$	(3,493	)	$	7,988	$	(15,759	)
Realized losses (gains) reclassified to investment income		—		—			—		72
Unrealized gain (loss) on available-for-sale securities, net	$	2,685	$	(3,493	)	$	7,988	$	(15,687	)

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


	Less than 12 Months					12 Months or Greater					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
September 30, 2023
U.S. government and agency securities	$	23,688	$	(68	)	$	61,885	$	(1,977	)	$	85,573	$	(2,045	)
Certificates of deposit		2,411		(24	)		3,753		(140	)		6,164		(164	)
Corporate bonds		38,793		(109	)		173,728		(4,235	)		212,521		(4,344	)
	$	64,892	$	(201	)	$	239,366	$	(6,352	)	$	304,258	$	(6,553	)


	Less than 12 Months					12 Months or Greater					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
December 31, 2022
U.S. government and agency securities	$	91,498	$	(2,014	)	$	38,495	$	(1,478	)	$	129,993	$	(3,492	)
Certificates of deposit		4,484		(144	)		2,087		(104	)		6,571		(248	)
Corporate bonds		106,707		(3,866	)		223,242		(6,937	)		329,949		(10,803	)
	$	202,689	$	(6,024	)	$	263,824	$	(8,519	)	$	466,513	$	(14,543	)

- Definition

Tabular disclosure of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-9

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 6: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (aa)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 7: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (aaa)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 8: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 9: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 10: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 11: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 12: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

+ Details

Liability Related to Sale of Future Royalties -Schedule of Activity Within Liability Related to Sale of Future Royalties (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Liability Related To Sale Of Future Royalties [Line Items]
Current portion of liability related to sale of future royalties	$ (52,750)	$ (48,601)
Non-current portion of liability related to sale of future royalties	53,096	$ 89,005
Royalty Agreements
Liability Related To Sale Of Future Royalties [Line Items]
Balance at December 31, 2022	137,606
Zolgensma royalties paid to HCR	(36,614)
Interest expense recognized	4,854
Balance at June 30, 2023	105,846
Current portion of liability related to sale of future royalties	(52,750)
Non-current portion of liability related to sale of future royalties	$ 53,096

Fair Value of Financial Instruments (Tables)

9 Months Ended

Sep. 30, 2023

Fair Value Disclosures [Abstract]

Schedule of Fair Value of Cash Equivalents and Marketable Securities

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


	Quoted		Significant
	prices		other		Significant
	in active		observable		unobservable
	markets		inputs		inputs
	(Level 1)		(Level 2)		(Level 3)		Total
September 30, 2023
Cash equivalents:
Money market mutual funds	$	—	$	30,966	$	—	$	30,966
Total cash equivalents		—		30,966		—		30,966
Marketable securities:
U.S. government and agency securities		—		92,551		—		92,551
Certificates of deposit		—		6,409		—		6,409
Corporate bonds		—		212,521		—		212,521
Total marketable securities		—		311,481		—		311,481
Total cash equivalents and marketable securities	$	—	$	342,447	$	—	$	342,447


	Quoted		Significant
	prices		other		Significant
	in active		observable		unobservable
	markets		inputs		inputs
	(Level 1)		(Level 2)		(Level 3)		Total
December 31, 2022
Cash equivalents:
Money market mutual funds	$	—	$	58,611	$	—	$	58,611
Corporate bonds		—		993		—		993
Total cash equivalents		—		59,604		—		59,604
Marketable securities:
U.S. government and agency securities		—		130,993		—		130,993
Certificates of deposit		—		7,308		—		7,308
Corporate bonds		—		329,949		—		329,949
Total marketable securities		—		468,250		—		468,250
Total cash equivalents and marketable securities	$	—	$	527,854	$	—	$	527,854

License and Collaboration Agreements - Schedule Of License Revenue (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
License Revenue [Line Items]
Other license revenue				$ 31
Interest income from licensing	$ 56	$ 18	$ 166	265
Novartis Gene Therapies [Member]
License Revenue [Line Items]
Total license and royalty revenue	28,364	25,205	63,454	75,161
Interest income from licensing	7	8	22	84
Zolgensma Royalties [Member]
License Revenue [Line Items]
Total license and royalty revenue	$ 28,364	$ 25,205	$ 63,454	$ 75,130

- Definition

+ References

+ Details

Summary of Significant Accounting Policies - Summary of Reconciliation of Cash and Cash Equivalents and Restricted Cash (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022
Accounting Policies [Abstract]
Cash and cash equivalents	$ 53,045	$ 96,952	$ 118,544
Restricted cash	2,255	$ 2,030	2,030
Total cash and cash equivalents and restricted cash	$ 55,300		$ 120,574

Related Party Transactions - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
FOXKISER LLP [Member] \| Service Agreements [Member] \| Research and Development Expense [Member] \| Related Party [Member]
Related Party Transaction [Line Items]
Related party transaction expense	$ 0	$ 0	$ 0	$ 2,400,000

License and Collaboration Agreements -Schedule of AbbVie Collaboration Agreement (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Net cost reimbursement to (from) AbbVie included in:
Total net cost reimbursement to (from) AbbVie	$ (18,993)	$ (3,495)	$ (55,293)	$ (11,385)
Abb Vie Collaboration And License Agreement \| Research and Development Expense [Member]
Net cost reimbursement to (from) AbbVie included in:
Total net cost reimbursement to (from) AbbVie	(19,608)	(4,245)	(56,300)	(12,339)
Abb Vie Collaboration And License Agreement \| General and Administrative Expense [Member]
Net cost reimbursement to (from) AbbVie included in:
Total net cost reimbursement to (from) AbbVie	$ 615	$ 750	$ 1,007	$ 954

Liability Related to Sale of Future Royalties - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Liability Related To Sale Of Future Royalties [Line Items]
Repurchase of call option amount			$ 300,000
Interest expense	$ 1,624	$ 5,954	5,499	$ 18,944
November 7, 2024
Liability Related To Sale Of Future Royalties [Line Items]
Repurchase of call option amount, before exercised			1,000
HCR [Member]
Liability Related To Sale Of Future Royalties [Line Items]
Proceeds from Royalties Received			4,000
Deferred Transaction Cost			3,500
Interest expense			$ 192,500
Interest Rate, Effective Percentage	5.20%		5.20%
HCR [Member] \| Other Noncurrent Liabilities
Liability Related To Sale Of Future Royalties [Line Items]
Proceeds from sale of future royalties			$ 196,000
HCR [Member] \| November 7, 2024
Liability Related To Sale Of Future Royalties [Line Items]
Royalty Payment Cap Amount			260,000
HCR [Member] \| November 8, 2024
Liability Related To Sale Of Future Royalties [Line Items]
Royalty Payment Cap Amount			300,000
HCR [Member] \| Royalty Agreements
Liability Related To Sale Of Future Royalties [Line Items]
Purchase Agreement			$ 200,000

Subsequent Events

9 Months Ended

Sep. 30, 2023

Subsequent Events [Abstract]

Subsequent Events

15. Subsequent Events

Restructuring Plans

In October 2023, the Company's Board of Directors approved a strategic pipeline prioritization and corporate restructuring designed to prioritize the development of ABBV-RGX-314, RGX-202 for the treatment of Duchenne muscular dystrophy, and RGX-121 for the treatment of Mucopolysaccharidosis Type II (MPS II). The restructuring includes a reduction in workforce and other operating expenses, primarily in rare neurodegenerative disease development, early research and other general and administrative areas.

As a result of the restructuring, the Company expects to reduce its workforce by approximately 15% beginning in November 2023. The Company estimates that it will incur restructuring costs of approximately $3.6 million in the fourth quarter of 2023, primarily associated with employee severance, continuing healthcare benefits and other related costs of the restructuring. The Company expects restructuring activities to be substantially completed by the fourth quarter of 2023 and cash payments related to restructuring costs to be substantially completed by the first quarter of 2024. The Company may also incur other charges or cash expenditures not currently contemplated due to events that may occur as a result of, or associated with, the restructuring.

Commitments and Contingencies - Additional Information (Detail) - University of Pennsylvania [Member] $ in Millions	1 Months Ended	9 Months Ended
	Mar. 31, 2022 USD ($)	Sep. 30, 2023 USD ($) Installment
Penn Letter Agreement [Member]
Other Commitments [Line Items]
Amount payable to agreement	$ 20.0	$ 20.0
Number of equal annual installments \| Installment		4
Related party transaction expense	9.2
Present value of cost of revenue	17.3
Sublicense fees previously recognized	$ 8.1
Amount payable to net present value discount		$ 7.8
Penn Letter Agreement [Member] \| Accrued Expenses and Other Current Liabilities [Member]
Other Commitments [Line Items]
Amount payable to net present value discount		2.3
Penn Letter Agreement [Member] \| Other Liabilities [Member]
Other Commitments [Line Items]
Amount payable to net present value discount		5.5
Sublicense Fees Due Or Owed in Future [Member]
Other Commitments [Line Items]
Amount payable to agreement		8.0
Other Past or Future Obligations to Pay Sublicense Fees [Member]
Other Commitments [Line Items]
Amount payable to agreement		12.0
First Anniversary [Member]
Other Commitments [Line Items]
Amount payable to agreement		$ 3.0

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Revenues
Revenues	$ 28,914	$ 26,512	$ 68,029	$ 81,379
Operating Expenses
Cost of revenues	12,388	13,094	25,975	41,762
Research and development	58,183	63,313	176,585	179,948
General and administrative	23,083	20,921	69,415	64,071
Other operating expenses	220	229	279	703
Total operating expenses	93,874	97,557	272,254	286,484
Loss from operations	(64,960)	(71,045)	(204,225)	(205,105)
Other Income (Expense)
Interest income from licensing	56	18	166	265
Investment income	4,660	1,497	8,953	3,357
Interest expense	(1,624)	(5,954)	(5,499)	(18,944)
Total other income (expense)	3,092	(4,439)	3,620	(15,322)
Loss before income taxes	(61,868)	(75,484)	(200,605)	(220,427)
Income Tax Benefit				41
Net loss	(61,868)	(75,484)	(200,605)	(220,386)
Other Comprehensive Income (Loss)
Unrealized gain (loss) on available-for-sale securities, net	2,685	(3,493)	7,988	(15,687)
Total other comprehensive income (loss)	2,685	(3,493)	7,988	(15,687)
Comprehensive loss	$ (59,183)	$ (78,977)	$ (192,617)	$ (236,073)
Net loss per share, basic	$ (1.41)	$ (1.75)	$ (4.6)	$ (5.11)
Net loss per share, diluted	$ (1.41)	$ (1.75)	$ (4.6)	$ (5.11)
Weighted-average common shares outstanding, basic	43,945	43,251	43,644	43,103
Weighted-average common shares outstanding, diluted	43,945	43,251	43,644	43,103
License and royalty [Member]
Revenues
Revenues	$ 28,914	$ 26,512	$ 68,029	$ 81,379

Fair Value of Financial Instruments - Schedule of Fair Value of Cash Equivalents and Marketable Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Marketable securities:
Fair Value	$ 311,481	$ 468,250
Cash Equivalents and Marketable Securities [Member]
Marketable securities:
Total cash equivalents and marketable securities	342,447	527,854
Corporate Bonds [Member]
Cash equivalents:
Total cash equivalents		993
Marketable securities:
Fair Value	212,521	329,949
Cash Equivalents [Member]
Cash equivalents:
Total cash equivalents	30,966	59,604
US Government and Agency Securities [Member]
Cash equivalents:
Total cash equivalents	92,551
Marketable securities:
Fair Value		130,993
Certificates of Deposit [Member]
Marketable securities:
Fair Value	6,409	7,308
Money Market Mutual Funds [Member] \| Cash Equivalents [Member]
Cash equivalents:
Total cash equivalents	30,966	58,611
Significant Other Observable Inputs (Level 2) [Member]
Marketable securities:
Fair Value	311,481	468,250
Significant Other Observable Inputs (Level 2) [Member] \| Cash Equivalents and Marketable Securities [Member]
Marketable securities:
Total cash equivalents and marketable securities	342,447	527,854
Significant Other Observable Inputs (Level 2) [Member] \| Corporate Bonds [Member]
Cash equivalents:
Total cash equivalents		993
Marketable securities:
Fair Value	212,521	329,949
Significant Other Observable Inputs (Level 2) [Member] \| Cash Equivalents [Member]
Cash equivalents:
Total cash equivalents	30,966	59,604
Significant Other Observable Inputs (Level 2) [Member] \| US Government and Agency Securities [Member]
Cash equivalents:
Total cash equivalents	92,551
Marketable securities:
Fair Value		130,993
Significant Other Observable Inputs (Level 2) [Member] \| Certificates of Deposit [Member]
Marketable securities:
Fair Value	6,409	7,308
Significant Other Observable Inputs (Level 2) [Member] \| Money Market Mutual Funds [Member] \| Cash Equivalents [Member]
Cash equivalents:
Total cash equivalents	$ 30,966	$ 58,611

Property and Equipment, Net

9 Months Ended

Sep. 30, 2023

Property, Plant and Equipment [Abstract]

Property and Equipment, Net

5. Property and Equipment, Net

Property and equipment, net consists of the following (in thousands):


	September 30, 2023			December 31, 2022
Laboratory and manufacturing equipment	$	75,214		$	71,801
Computer equipment and software		5,748			4,910
Furniture and fixtures		7,078			6,965
Leasehold improvements		101,868			99,397
Total property and equipment		189,908			183,073
Accumulated depreciation and amortization		(54,374	)		(41,388	)
Property and equipment, net	$	135,534		$	141,685

Nature of Business - Additional Information (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accumulated deficit	$ (642,158)	$ (441,553)
Cash, cash equivalents and marketable securities	$ 364,500

- Definition

Amount of accumulated undistributed earnings (deficit).

+ References + Details

Supplemental Disclosures - Additional Information (Detail) - USD ($)	9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Payables and Accruals [Abstract]
Purchases of property and equipment included in accounts payable and accrued expenses and other current liabilities	$ 500,000	$ 3,100,000
Increase (decrease) in purchases of property and equipment included in accounts payable and accrued expenses and other current liabilities			$ (2,000,000)	$ (7,000,000)
Offering expenses for ATM Program	$ 400,000	$ 0

License and Collaboration Agreements - Summary of Changes in Allowance For Credit Losses (Detail) - Accounts Receivable $ in Thousands	9 Months Ended
	Sep. 30, 2023 USD ($)
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning Balance	$ 4,152
Changes in present value discount of receivables	322
Ending Balance	$ 4,474

- Definition

Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

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