Summary of Stock Awards Granted (Parenthetical) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants, Stock options		54,575	207,583	1,084,924	1,499,120
Grants, Stock options	[1]	33,752	147,075	1,109,663	859,510
Stock-based compensation Grants				$ 7,400
Stock-based compensation expense		$ 47,377	$ 102,892	$ 88,627	$ 132,090
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation granted under plan vest period				4 years
Stock-based compensation expense		$ 21,135	$ 89,155	$ 44,965	$ 105,561
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants, Stock options		502,225	38,500	502,225	38,500
Grants, Stock options		394,975		394,975
Share based compensation granted under plan vest period				1 year 8 months 12 days
Share-based payment arrangement, Cost not yet recognized, Amount		$ 54,200		$ 54,200
Stock-based compensation expense				$ 22,400
Remaining shares associated with performance condition		394,975
Vesting PSUs				394,975

[1] Included in restricted stock units (“RSUs”) for the three and six months ended June 30, 2023 and 2022 are 502,225 and 38,500 shares, respectively, with performance conditions (“PSUs”) which are related to regulatory approval of certain of the Company's product candidates. As a result of the regulatory approval of ELEVIDYS in June 2023, the Compensation Committee of the Company's Board of Directors determined that one of the performance conditions was met, resulting in the recognition of stock-based compensation expense of $7.4 million associated with 394,975 PSUs with performance conditions during the three and six months ended June 30, 2023. Vesting of the 394,975 PSUs with performance conditions achieved is contingent on the fulfillment of remaining service conditions. The remaining expense associated with the 394,975 PSUs with performance conditions achieved is $54.2 million and will be recognized over approximately the next 1.7 years. If the performance milestones are met within the required time frame for the remaining PSUs, the Company may recognize up to $22.4 million of stock-based compensation expense. Stock options and the remaining RSUs granted during the periods presented in the table have only service-based criteria and vest over four years.