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Long-Term Debt - Additional Information (Detail) (USD $)	12 Months Ended			0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Sep. 24, 2014	Sep. 24, 2013	Oct. 01, 2014	Sep. 30, 2014	Apr. 01, 2014	Mar. 31, 2014
Debt Instrument [Line Items]
Deferred financing costs	$ 35,500,000us-gaap_DeferredFinanceCostsNet
Amortization of Financing Costs	6,400,000us-gaap_AmortizationOfFinancingCosts	4,500,000us-gaap_AmortizationOfFinancingCosts	3,000,000us-gaap_AmortizationOfFinancingCosts
Collateral, Percent of reserve value required	80.00%oas_DebtInstrumentCollateralOilandGasPropertiesEligiblePercentofReserveValueRequired
Two Thousand Twenty Two Notes [Member]
Debt Instrument [Line Items]
Senior unsecured debt principal amount					1,000,000,000.0us-gaap_DebtInstrumentFaceAmount / us-gaap_DebtInstrumentAxis = oas_TwoThousandTwentyTwoNotesMember
Senior unsecured notes stated interest rate					6.875%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = oas_TwoThousandTwentyTwoNotesMember
Net proceeds from issuance of notes				983,600,000us-gaap_ProceedsFromIssuanceOfUnsecuredDebt / us-gaap_DebtInstrumentAxis = oas_TwoThousandTwentyTwoNotesMember
Two Thousand Nineteen Notes [Member]
Debt Instrument [Line Items]
Senior unsecured debt principal amount			400,000,000.0us-gaap_DebtInstrumentFaceAmount / us-gaap_DebtInstrumentAxis = oas_TwoThousandNineteenNotesMember
Senior unsecured notes stated interest rate			7.25%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = oas_TwoThousandNineteenNotesMember
Two Thousand Twenty One Notes [Member]
Debt Instrument [Line Items]
Senior unsecured debt principal amount			400,000,000.0us-gaap_DebtInstrumentFaceAmount / us-gaap_DebtInstrumentAxis = oas_TwoThousandTwentyOneNotesMember
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Two Thousand Twenty Three Notes [Member]
Debt Instrument [Line Items]
Senior unsecured debt principal amount			400,000,000.0us-gaap_DebtInstrumentFaceAmount / us-gaap_DebtInstrumentAxis = oas_TwoThousandTwentyThreeNotesMember
Senior unsecured notes stated interest rate			6.875%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = oas_TwoThousandTwentyThreeNotesMember
Unsecured Senior Notes [Member]
Debt Instrument [Line Items]
Net proceeds from issuance of notes			1,175,800,000us-gaap_ProceedsFromIssuanceOfUnsecuredDebt / us-gaap_DebtInstrumentAxis = oas_UnsecuredSeniorNotesMember
Redemption percentage, maximum	35.00%oas_RedemptionPercentageMaximum / us-gaap_DebtInstrumentAxis = oas_UnsecuredSeniorNotesMember
Percentage of minimum outstanding principal amount	65.00%oas_PercentageOfMinimumOutstandingPrincipalAmount / us-gaap_DebtInstrumentAxis = oas_UnsecuredSeniorNotesMember
Event of default by payment default	10,000,000.0oas_EventOfDefaultByPaymentDefault / us-gaap_DebtInstrumentAxis = oas_UnsecuredSeniorNotesMember
Event of default by final judgments	10,000,000.0oas_EventOfDefaultByFinalJudgments / us-gaap_DebtInstrumentAxis = oas_UnsecuredSeniorNotesMember
Long-term Debt	2,200,000,000us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = oas_UnsecuredSeniorNotesMember
Amended Credit Facility [Member]
Debt Instrument [Line Items]
Commitment fee of borrowing base capacity not utilized	0.375%us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage / us-gaap_DebtInstrumentAxis = oas_AmendedCreditFacilityMember
Long-term Debt	500,000,000us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = oas_AmendedCreditFacilityMember
Outstanding letters of credit	5,200,000us-gaap_LettersOfCreditOutstandingAmount / us-gaap_DebtInstrumentAxis = oas_AmendedCreditFacilityMember
Letter of credit unused borrowing base capacity	994,800,000us-gaap_DebtInstrumentUnusedBorrowingCapacityAmount / us-gaap_DebtInstrumentAxis = oas_AmendedCreditFacilityMember
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility maximum increase to aggregate commitments						2,000,000,000.0oas_LineOfCreditFacilityMaximumIncreaseToAggregateCommitments / us-gaap_LongtermDebtTypeAxis = us-gaap_RevolvingCreditFacilityMember	1,750,000,000.0oas_LineOfCreditFacilityMaximumIncreaseToAggregateCommitments / us-gaap_LongtermDebtTypeAxis = us-gaap_RevolvingCreditFacilityMember	1,750,000,000.0oas_LineOfCreditFacilityMaximumIncreaseToAggregateCommitments / us-gaap_LongtermDebtTypeAxis = us-gaap_RevolvingCreditFacilityMember	1,500,000,000.0oas_LineOfCreditFacilityMaximumIncreaseToAggregateCommitments / us-gaap_LongtermDebtTypeAxis = us-gaap_RevolvingCreditFacilityMember
Line of credit facility, maximum borrowing capacity	1,500,000,000.0us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity / us-gaap_LongtermDebtTypeAxis = us-gaap_RevolvingCreditFacilityMember
Line of credit facility, capacity available for specific purpose other than for trade purchases	$ 2,500,000,000.0us-gaap_LineOfCreditFacilityCapacityAvailableForSpecificPurposeOtherThanForTradePurchases / us-gaap_LongtermDebtTypeAxis = us-gaap_RevolvingCreditFacilityMember
Debt, Weighted Average Interest Rate	1.90%us-gaap_DebtWeightedAverageInterestRate / us-gaap_LongtermDebtTypeAxis = us-gaap_RevolvingCreditFacilityMember	1.80%us-gaap_DebtWeightedAverageInterestRate / us-gaap_LongtermDebtTypeAxis = us-gaap_RevolvingCreditFacilityMember
Unsecured Debt [Member]
Debt Instrument [Line Items]
Redemption term	180 days
Current Ratio [Member] | Amended Credit Facility [Member]
Debt Instrument [Line Items]
Minimum current ratio	1.0oas_MinimumCurrentRatio / us-gaap_DebtInstrumentAxis = oas_AmendedCreditFacilityMember / us-gaap_DebtSecurityAxis = oas_CurrentRatioMember
Minimum [Member] | EBITDAX [Member] | Amended Credit Facility [Member]
Debt Instrument [Line Items]
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- Definition

Debt Instrument, Collateral, Oil and Gas Properties Eligible, Percent of Reserve Value Required

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Amount of noncash expense included in interest expense to issue debt and obtain financing associated with the related debt instruments. Alternate captions include noncash interest expense.

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Face (par) amount of debt instrument at time of issuance.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Amount of unused borrowing capacity under the long-term financing arrangement that is available to the entity as of the balance sheet date.

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