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Subsequent Events - Additional Information (Detail) (Not Designated as Hedging Instrument [Member], Energy Related Derivative [Member], Subsequent Event [Member])
Feb. 28, 2015
MBbls
2015 Swap Agreement [Member]
  
Subsequent Event [Line Items]  
Total notional amount of oil barrels 122invest_DerivativeNonmonetaryNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= oas_TwoThousandFifteenSwapAgreementMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
2016 Swap Agreement [Member]
  
Subsequent Event [Line Items]  
Total notional amount of oil barrels 62invest_DerivativeNonmonetaryNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= oas_TwoThousandSixteenSwapAgreementMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember