License and Collaboration Agreements - Schedule Of License Revenue (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License Revenue		$ 3,500	$ 3,500
Interest income from licensing	$ 719	4,271	2,951
Novartis Gene Therapies [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total license and royalty revenue	94,978	145,131	24,329
Interest income from licensing	22	26	29
Zolgensma Royalties [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total license and royalty revenue	$ 94,978	61,631	$ 20,829
Achievement Of Sales Based Milestone For Zolgensma [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total license and royalty revenue		$ 80,000