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Summary of Significant Accounting Policies - Additional Information (Detail) (USD $) | 12 Months Ended | 1 Months Ended | 9 Months Ended
--- | --- | --- | ---
Dec. 31, 2014 counterparty | Dec. 31, 2013 | Dec. 31, 2012 | Mar. 31, 2014 | Feb. 17, 2015
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property, Plant and Equipment [Line Items] |  |  |  |  |
Proceeds from sale of property | $ 324,852,000 us-gaap_ProceedsFromSaleOfOilAndGasPropertyAndEquipment |  |  |  |
Gain on sale of properties | 186,999,000 us-gaap_GainLossOnSaleOfProperty | 0 us-gaap_GainLossOnSaleOfProperty | 0 us-gaap_GainLossOnSaleOfProperty |  |
Impairment of oil and gas properties | 47,238,000 us-gaap_ImpairmentOfOilAndGasProperties | 1,168,000 us-gaap_ImpairmentOfOilAndGasProperties | 3,581,000 us-gaap_ImpairmentOfOilAndGasProperties |  |
Capitalized interest costs | 8,800,000 us-gaap_InterestCostsCapitalized | 4,600,000 us-gaap_InterestCostsCapitalized | 3,300,000 us-gaap_InterestCostsCapitalized |  |
Capitalized Exploratory Well Costs that Have Been Capitalized for Period Greater than One Year | 0 us-gaap_CapitalizedExploratoryWellCostsThatHaveBeenCapitalizedForPeriodGreaterThanOneYear |  |  |  |
Derivative, number of counterparties | 7 oas_DerivativeNumberofCounterparties |  |  |  |
Past-due receivables from counterparties | 0 us-gaap_FinancingReceivableRecordedInvestmentPastDue |  |  |  |
Restricted stock awards vesting period | 3 years |  |  |  |
1 to 12 months [Member] |  |  |  |  |
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property, Plant and Equipment [Line Items] |  |  |  |  |
Contractual commodity derivative volume, percent | 110.00%oas_PortionOfFutureOilAndGasProductionPercentage / us-gaap_CreationDateAxis = oas_TwoThousandFourteenMember |  |  |  |
13 to 24 months [Member] |  |  |  |  |
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property, Plant and Equipment [Line Items] |  |  |  |  |
Contractual commodity derivative volume, percent | 100.00%oas_PortionOfFutureOilAndGasProductionPercentage / us-gaap_CreationDateAxis = oas_TwoThousandAndFifteenMember |  |  |  |
25 to 36 months [Member] |  |  |  |  |
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property, Plant and Equipment [Line Items] |  |  |  |  |
Contractual commodity derivative volume, percent | 75.00%oas_PortionOfFutureOilAndGasProductionPercentage / us-gaap_CreationDateAxis = oas_TwoThousandAndSixteenMember |  |  |  |
37 to 60 months [Member] |  |  |  |  |
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property, Plant and Equipment [Line Items] |  |  |  |  |
Contractual commodity derivative volume, percent | 50.00%oas_PortionOfFutureOilAndGasProductionPercentage / us-gaap_CreationDateAxis = oas_TwoThousandAndSixteenThereafterMember |  |  |  |
Minimum [Member] |  |  |  |  |
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property, Plant and Equipment [Line Items] |  |  |  |  |
Annual Forfeiture Rate | 0.00%oas_AnnualForfeitureRate / us-gaap_RangeAxis = us-gaap_MinimumMember |  |  |  |
Maximum [Member] |  |  |  |  |
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property, Plant and Equipment [Line Items] |  |  |  |  |
Annual Forfeiture Rate | 12.70%oas_AnnualForfeitureRate / us-gaap_RangeAxis = us-gaap_MaximumMember |  |  |  |
Non-Operated OIl and Natural Gas Properties [Member] |  |  |  |  |
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property, Plant and Equipment [Line Items] |  |  |  |  |
Proceeds from sale of property |  |  |  | 324,900,000 us-gaap_ProceedsFromSaleOfOilAndGasPropertyAndEquipment / us-gaap_PropertyPlantAndEquipmentByTypeAxis = oas_NonOperatedOIlandNaturalGasPropertiesMember |
Gain on sale of properties |  |  |  | 187,000,000 us-gaap_GainLossOnSaleOfProperty / us-gaap_PropertyPlantAndEquipmentByTypeAxis = oas_NonOperatedOIlandNaturalGasPropertiesMember |
Building [Member] |  |  |  |  |
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property, Plant and Equipment [Line Items] |  |  |  |  |
Estimated life of assets | 20 years |  |  |  |
Proved oil and gas properties [Member] |  |  |  |  |
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property, Plant and Equipment [Line Items] |  |  |  |  |
Impairment of oil and gas properties | 40,000,000 us-gaap_ImpairmentOfOilAndGasProperties / us-gaap_PropertyPlantAndEquipmentByTypeAxis = oas_ProvedOilAndGasPropertiesMember | 0 us-gaap_ImpairmentOfOilAndGasProperties / us-gaap_PropertyPlantAndEquipmentByTypeAxis = oas_ProvedOilAndGasPropertiesMember | 0 us-gaap_ImpairmentOfOilAndGasProperties / us-gaap_PropertyPlantAndEquipmentByTypeAxis = oas_ProvedOilAndGasPropertiesMember |  |
Unproved Oil And Gas Properties [Member] |  |  |  |  |
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property, Plant and Equipment [Line Items] |  |  |  |  |
Impairment of oil and gas properties | 7,300,000 us-gaap_ImpairmentOfOilAndGasProperties / us-gaap_PropertyPlantAndEquipmentByTypeAxis = oas_UnprovedOilAndGasPropertiesMember | 1,200,000 us-gaap_ImpairmentOfOilAndGasProperties / us-gaap_PropertyPlantAndEquipmentByTypeAxis = oas_UnprovedOilAndGasPropertiesMember | 3,600,000 us-gaap_ImpairmentOfOilAndGasProperties / us-gaap_PropertyPlantAndEquipmentByTypeAxis = oas_UnprovedOilAndGasPropertiesMember |  |
Salt Water Disposal Facility [Member] |  |  |  |  |
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property, Plant and Equipment [Line Items] |  |  |  |  |
Estimated life of assets | 30 years |  |  |  |
Furniture and equipment [Member] | Minimum [Member] |  |  |  |  |
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property, Plant and Equipment [Line Items] |  |  |  |  |
Estimated life of assets | 2 years |  |  |  |
Furniture and equipment [Member] | Maximum [Member] |  |  |  |  |
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property, Plant and Equipment [Line Items] |  |  |  |  |
Estimated life of assets | 7 years |  |  |  |
Domestic Tax Authority [Member] |  |  |  |  |
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property, Plant and Equipment [Line Items] |  |  |  |  |
Stock-based compensation related to unrealized excess tax benefits | 9,500,000 oas_StockbasedCompensationRelatedToUnrealizedExcessTaxBenefits / us-gaap_IncomeTaxAuthorityAxis = us-gaap_DomesticCountryMember |  |  |  |
State and Local Jurisdiction [Member] |  |  |  |  |
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property, Plant and Equipment [Line Items] |  |  |  |  |
Stock-based compensation related to unrealized excess tax benefits | $ 7,400,000 oas_StockbasedCompensationRelatedToUnrealizedExcessTaxBenefits / us-gaap_IncomeTaxAuthorityAxis = us-gaap_StateAndLocalJurisdictionMember |  |  |  |
Subsequent Event [Member] |  |  |  |  |
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property, Plant and Equipment [Line Items] |  |  |  |  |
Spot Price Decrease, Crude Oil, Percentage |  |  |  |  | 50.00%oas_SpotPriceDecreaseCrudeOilPercentage / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
Spot Price Decrease, Natural Gas, Percentage |  |  |  |  | 40.00%oas_SpotPriceDecreaseNaturalGasPercentage / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember

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