Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Line Items]
Losses incurred	$ (141,674,000)	$ (77,067,000)	$ (108,645,000)	$ (35,224,000)	$ (25,840,000)	$ (45,723,000)	$ (63,155,000)	$ 86,090,000	$ (362,610,000)	$ (48,628,000)	$ (267,265,000)
Net change in valuation allowance for deferred tax assets									164,800,000	(69,500,000)
Net operating loss carried forward	212,342,000				144,897,000				212,342,000	144,897,000
Accrual for interest or penalties	0				$ 0				$ 0	0
Recognized interest and/or penalties										0	0
Minimum [Member]
Income Taxes [Line Items]
Operating loss carryforwards, ending of expiration year									2019
Maximum [Member]
Income Taxes [Line Items]
Operating loss carryforwards, ending of expiration year									2038
Federal [Member]
Income Taxes [Line Items]
Net operating loss carryforwards	438,500,000								$ 438,500,000
Net operating loss carryforwards subject to expiration	240,000,000								240,000,000
Net operating loss carried forward	198,500,000								198,500,000
State [Member]
Income Taxes [Line Items]
Net operating loss carryforwards	503,300,000								503,300,000
Net operating loss carryforwards subject to expiration	503,300,000								$ 503,300,000
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 2019 and 2038 and between 2019 and 2033, respectively.
Research and Development Credits [Member] | Federal [Member]
Income Taxes [Line Items]
Research and development credits carryforward, Amount	50,300,000								$ 50,300,000
Research and Development Credits [Member] | Federal [Member] | Minimum [Member]
Income Taxes [Line Items]
Research and development credits carryforward, Expiration period									2019
Research and Development Credits [Member] | Federal [Member] | Maximum [Member]
Income Taxes [Line Items]
Research and development credits carryforward, Expiration period									2038
Research and Development Credits [Member] | State [Member]
Income Taxes [Line Items]
Research and development credits carryforward, Amount	20,900,000								$ 20,900,000
Research and Development Credits [Member] | State [Member] | Minimum [Member]
Income Taxes [Line Items]
Research and development credits carryforward, Expiration period									2019
Research and Development Credits [Member] | State [Member] | Maximum [Member]
Income Taxes [Line Items]
Research and development credits carryforward, Expiration period									2033
Sarepta International C.V. [Member]
Income Taxes [Line Items]
Losses incurred									$ 67,600,000	$ 143,800,000	$ 174,900,000
Net operating loss carried forward	67,600,000								$ 67,600,000
Sarepta International C.V. [Member] | Minimum [Member]
Income Taxes [Line Items]
Operating loss carryforwards, ending of expiration year									2036
Sarepta International C.V. [Member] | Maximum [Member]
Income Taxes [Line Items]
Operating loss carryforwards, ending of expiration year									2037
Sarepta International C.V. [Member] | Federal [Member]
Income Taxes [Line Items]
Net operating loss carryforwards	386,300,000								$ 386,300,000
Net operating loss carryforwards subject to expiration	318,700,000								318,700,000
Sarepta International Holdings GmbH [Member] | Foreign [Member]
Income Taxes [Line Items]
Net operating loss carryforwards	$ 55,200,000								$ 55,200,000
Operating loss carryforwards, ending of expiration year									2024