Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended				12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Line Items]
U.S. federal corporate tax rate						34.00%	34.00%	34.00%
State income tax liability	$ 1,800,000					$ 1,800,000
Current federal income tax						$ 200,000
Alternative minimum tax partially refundable year one						2018
Alternative minimum tax partially refundable year two						2019
Alternative minimum tax partially refundable year three						2020
Alternative minimum tax fully refundable year one						2021
Current federal income tax							$ 0	$ 0
State income taxes							0	0
Foreign income taxes							0	0
Domestic pre-tax losses						$ 45,700,000
Foreign pre-tax losses						2,900,000
Reduction to deferred tax assets						87,000,000
Impact on net tax						0
Losses incurred	(25,840,000)	$ (45,723,000)	$ (63,155,000)	$ 86,090,000		(48,628,000)	(267,265,000)	(220,030,000)
Net change in valuation allowance for deferred tax assets						69,500,000	54,200,000
Accrual for interest or penalties	0					0	0
Recognized interest and/or penalties						0	0	$ 0
Federal [Member]
Income Taxes [Line Items]
Net operating loss carryforwards	249,300,000					249,300,000
State [Member]
Income Taxes [Line Items]
Net operating loss carryforwards	174,800,000					$ 174,800,000
Foreign
Income Taxes [Line Items]
Operating loss carryforwards, ending of expiration year						2024
Net operating loss carryforwards	2,900,000					$ 2,900,000
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 2018 and 2037 and between 2018 and 2032, respectively.
Research and Development Credits [Member] | Federal [Member]
Income Taxes [Line Items]
Research and development credits carryforward, Amount	34,300,000					$ 34,300,000
Research and Development Credits [Member] | State [Member]
Income Taxes [Line Items]
Research and development credits carryforward, Amount	11,500,000					11,500,000
Sarepta International C.V. [Member]
Income Taxes [Line Items]
Losses incurred						172,800,000	$ 214,300,000
Sarepta International C.V. [Member] | Federal [Member]
Income Taxes [Line Items]
Net operating loss carryforwards	$ 387,100,000					$ 387,100,000
Scenario, Forecast [Member]
Income Taxes [Line Items]
U.S. federal corporate tax rate					21.00%
Maximum [Member]
Income Taxes [Line Items]
U.S. federal corporate tax rate						35.00%
Operating loss carryforwards, ending of expiration year						2037
Maximum [Member] | Research and Development Credits [Member] | Federal [Member]
Income Taxes [Line Items]
Research and development credits carryforward, Expiration period						2037
Maximum [Member] | Research and Development Credits [Member] | State [Member]
Income Taxes [Line Items]
Research and development credits carryforward, Expiration period						2032
Maximum [Member] | Sarepta International C.V. [Member]
Income Taxes [Line Items]
Operating loss carryforwards, ending of expiration year						2037
Minimum [Member]
Income Taxes [Line Items]
Operating loss carryforwards, ending of expiration year						2018
Minimum [Member] | Research and Development Credits [Member] | Federal [Member]
Income Taxes [Line Items]
Research and development credits carryforward, Expiration period						2018
Minimum [Member] | Research and Development Credits [Member] | State [Member]
Income Taxes [Line Items]
Research and development credits carryforward, Expiration period						2018
Minimum [Member] | Sarepta International C.V. [Member]
Income Taxes [Line Items]
Operating loss carryforwards, ending of expiration year						2036