License and Collaboration Agreements - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Product revenues, net	$ 429,771	$ 309,322	$ 1,149,803	$ 779,805
Total Roche supply agreement revenue	37,401	22,495	93,764	66,750
Development Milestone and Upfront Fee Recognized as Research and Development Expense	0	3,800	0	11,900
ELEVIDYS [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Product revenues, net	180,983	69,108	436,640	69,108
Collaborative Arrangement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payment for option exercise			116,800
Research, option and milestone expense	0		0
Up-front and development milestone expenses				7,500
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			2,700,000
Collaborative Arrangement | Research and Development Expense [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development expense		3,800		3,800
Collaborative Arrangement | Roche Holding A.G. [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Product revenues, net		22,500	48,000	66,800
Deferred Revenue	452,000		452,000		$ 487,400
Deferred Revenue, Current	127,000		127,000		50,400
Research and development expense	61,500	34,900	101,100	83,400
Collaboration Receivable	$ 66,400		$ 66,400		$ 29,800
Collaborative Arrangement | Roche Holding A.G. [Member] | ELEVIDYS [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total Roche supply agreement revenue		$ 0		$ 0