License and Royalty Revenue - Additional Information (Detail) $ in Thousands				1 Months Ended		3 Months Ended		12 Months Ended
	May 31, 2020 USD ($)	Apr. 01, 2020 USD ($)	Nov. 30, 2018	Apr. 30, 2021 USD ($)	Nov. 30, 2018	Mar. 31, 2021 USD ($) ProductCandidate	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
License Revenue [Line Items]
Milestone payment upon commencement of clinical trials in humans						$ 23,300
Milestone payment upon submission of regulatory approval filings						21,000
Milestone payment upon approval of commercial products by regulatory agencies						93,500
Milestone payment upon achievement of specified sales targets for licensed products						57,000
Deferred revenue, current and non-current						4,124	$ 3,333	$ 4,232	$ 3,333
Provision for credit losses						565	0
Interest income from licensing						29	848
Novartis Gene Therapies [Member]
License Revenue [Line Items]
Interest income from licensing						6	$ 7
Abeona Therapeutics Inc. [Member] | November 2018 License Agreement Termination [Member]
License Revenue [Line Items]
Up-front and anuual fees		$ 20,000
March 2014 License Agreement [Member] | Novartis Gene Therapies [Member]
License Revenue [Line Items]
Accounts receivable						18,100		19,600
November 2018 License Agreement [Member] | Abeona Therapeutics Inc. [Member]
License Revenue [Line Items]
Provision for credit losses						600
Accounts receivable						30,100		30,100
License fee		8,000
Allowance for doubtful accounts receivable						8,200		7,700
November 2018 License Agreement [Member] | Abeona Therapeutics Inc. [Member] | November 2018 License Agreement Termination [Member]
License Revenue [Line Items]
Accounts receivable	$ 28,000					30,100
License agreement termination claims, description	subsequent to the termination of the November 2018 License, Abeona filed a claim in arbitration alleging that the Company had breached certain responsibilities to communicate with Abeona regarding the Company’s prosecution of licensed patents under the November 2018 License. The Company disputes Abeona’s claim and filed a counterclaim in arbitration demanding payment of the $28.0 million of unpaid fees from Abeona, plus accrued interest.		As a result of the termination, Abeona was required to pay a $20.0 million license fee to the Company within 15 days of the termination date, which otherwise would have been due to the Company in November 2020.
Interest percentage on unpaid balances under license agreement					1.50%
Interest income from licensing						2,100		$ 2,100
November 2018 License Agreement [Member] | Abeona Therapeutics Inc. [Member] | Subsequent Event | November 2018 License Agreement Termination [Member]
License Revenue [Line Items]
License fee				$ 28,000
November Two Thousand Eighteen Due | Abeona Therapeutics Inc. [Member]
License Revenue [Line Items]
License fee	$ 20,000	$ 8,000
Maximum [Member]
License Revenue [Line Items]
Aggregate milestone payment for all the targets						$ 194,800
N A V Technology Platform [Member]
License Revenue [Line Items]
Number of commercial product candidates | ProductCandidate						1
N A V Technology Platform [Member] | Minimum [Member]
License Revenue [Line Items]
Number of development partnered product candidates | ProductCandidate						20
Zolgensma Royalties [Member] | March 2014 License Agreement [Member] | Novartis Gene Therapies [Member]
License Revenue [Line Items]
Accounts receivable, current						$ 13,200
H C R [Member] | March 2014 License Agreement [Member] | Novartis Gene Therapies [Member]
License Revenue [Line Items]
Accounts receivable, current						$ 13,200