Stock Based Compensation - Summary of Restricted Stock Unit Activity (Detail) - Restricted Stock Units (RSUs) [Member]	12 Months Ended
	Dec. 31, 2024 $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares, Grants outstanding at beginning of the period | shares	2,240,504	[1]
Shares, Granted | shares	1,409,347	[2]
Shares, Vested | shares	(734,922)
Shares, Forfeited | shares	(197,515)
Shares, Grants outstanding at end of the period | shares	2,717,414
Weighted Average Grant Date Fair Value per Share, Grants outstanding at beginning of the period | $ / shares	$ 120.17
Weighted Average Grant Date Fair Value per Share, Granted | $ / shares	129.31
Weighted Average Grant Date Fair Value per Share, Vested | $ / shares	107.93
Weighted Average Grant Date Fair Value per Share, Forfeited | $ / shares	126.19
Weighted Average Grant Date Fair Value per Share, Grants outstanding at end of the period | $ / shares	$ 127.78

[1] (1) Included in RSUs outstanding at the beginning of the year ended December 31, 2024 are 33,000 shares of PSUs (the “March 2022 PSU”) with performance conditions related to regulatory approval of certain of the Company's product candidates and 485,275 shares of PSUs (the “March 2023 PSU”) with performance conditions related to regulatory approval of certain of the Company's product candidates and the achievement of a certain financial performance target.

[2] (2) Included in RSUs granted during the year ended December 31, 2024 are 97,460 shares with performance conditions (the “March 2024 PSU”), which are related to the achievement of certain financial performance targets and regulatory approval of certain of the Company's product candidates and 24,500 shares of the March 2023 PSU, which are related to the achievement of a certain financial performance target.   Stock options and the remaining RSUs granted during the year ended December 31, 2024 have only service-based criteria and vest over four years.   As of December 31, 2024, the following PSUs became vested or eligible for vesting: • March 2022 PSU: The expanded regulatory approval of ELEVIDYS in June 2024 resulted in 33,000 shares becoming eligible for vesting, which is contingent on the fulfillment of remaining service conditions. • March 2023 PSU: The achievement of a certain financial performance target during the year ended December 31, 2024 resulted in 24,500 shares becoming eligible for vesting, which is contingent on the fulfillment of remaining service conditions. • March 2024 PSU: The expanded regulatory approval of ELEVIDYS in June 2024 resulted in the cliff-vesting of 44,300 of the 97,460 shares of the March 2024 PSU during the year ended December 31, 2024.   As of December 31, 2024, none of the remaining performance conditions associated with the March 2022 PSU and March 2024 PSU were probable of being achieved.