License and Collaboration Agreements - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Product revenues, net	$ 360,548	$ 238,988	$ 720,032	$ 470,483
Collaboration receivable	19,869		19,869		$ 29,786
Development Milestone and Upfront Fee Recognized as Research and Development Expense	0	7,600	0	8,100
ELEVIDYS [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Product revenues, net	121,721	0	255,657	0
Collaborative Arrangement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payment for option exercise			121,800
Research, option and milestone expense	0		0
Collaborative Arrangement | Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent research milestone payments			34,800
Development Milestone and Upfront Fee Recognized as Research and Development Expense			2,800,000
Collaborative Arrangement | Research and Development Expense
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Up-front and development milestone expenses		7,500		7,500
Collaborative Arrangement | Roche Holding A.G. [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Product revenues, net		22,300	48,000	44,300
Deferred Revenue	447,000		447,000		487,400
Deferred Revenue, Current	122,000		122,000		50,400
Research and development expense	17,900	28,200	39,600	48,500
Collaboration Receivable	19,900		19,900		$ 29,800
Collaborative Arrangement | Roche Holding A.G. [Member] | ELEVIDYS [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Inventory Cost			1,700
Collaboration receivable	5,800	0	5,800	0
Royalty revenue	$ 2,400	$ 0	$ 2,600	$ 0