Income Taxes - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
	Feb. 28, 2019	Dec. 31, 2021	Dec. 31, 2020
Income Taxes [Line Items]
Net change in valuation allowance for deferred tax assets		$ 66,500,000	$ 117,000,000.0
Net operating loss carried forwards		330,392,000	333,703,000
Accrual for interest or penalties		0	0
Recognized interest and/or penalties		$ 0	$ 0
Minimum [Member]
Income Taxes [Line Items]
Operating loss carryforwards, ending of expiration year		2022
Maximum [Member]
Income Taxes [Line Items]
Operating loss carryforwards, ending of expiration year		2041
Federal [Member]
Income Taxes [Line Items]
Net operating loss carryforwards		$ 1,280,400,000
Net operating loss carryforwards subject to expiration		577,200,000
Net operating loss carried forwards		703,200,000
State [Member]
Income Taxes [Line Items]
Net operating loss carryforwards		841,200,000
Net operating loss carryforwards subject to expiration		797,000,000.0
Net operating loss carried forwards		44,200,000
Foreign [Member] | Sarepta International Holdings GmbH [Member]
Income Taxes [Line Items]
Net operating loss carryforwards		$ 13,600,000
Research and Development Credits [Member]
Income Taxes [Line Items]
Research and development credits carryforward, Description		These federal and state research and development credits begin to expire between 2022 and 2041 and between 2022 and 2036, respectively.
Research and Development Credits [Member] | Federal [Member]
Income Taxes [Line Items]
Research and development credits carryforward, Amount		$ 139,200,000
Research and Development Credits [Member] | State [Member]
Income Taxes [Line Items]
Research and development credits carryforward, Amount		$ 77,000,000.0
Warrant Agreement | Myonexus Therapeutics, Inc. [Member]
Income Taxes [Line Items]
Accumulated costs related to acquisition	$ 253,700,000
Up-front and milestone payments	85,000,000.0
Exercise option	$ 168,700,000