Reconciliation Between Effective Tax Rate and Federal Income Tax Rate (Detail)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Federal income tax rate	21.00%	34.00%	34.00%
State taxes	12.30%	(27.70%)
Research and development and other tax credits	3.10%	8.50%	1.50%
Valuation allowance	(45.50%)	(93.20%)	(17.30%)
Permanent differences	6.90%	6.40%	(3.40%)
Sarepta International C.V. return to provision	(0.10%)	62.10%
Impact of tax reform, net of valuation allowance		5.90%
Foreign rate differential	(0.90%)	(0.60%)	(14.80%)
Other	3.40%	0.40%
Effective tax rate	0.20%	(4.20%)

Effective income tax rate reconciliation impact of tax reform, net of valuation allowance.

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Effective income tax rate reconciliation, permanent differences.

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Effective income tax rate reconciliation research and development and other tax credit.

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Effective income tax rate reconciliation return to provision.

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to changes in the valuation allowance for deferred tax assets.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations applicable to statutory income tax expense (benefit) outside of the country of domicile.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations applicable to state and local income tax expense (benefit), net of federal tax expense (benefit).

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