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Assets Held for Sale and Divestiture - Additional Information (Details) (USD $)
In Thousands, unless otherwise specified
12 Months Ended 1 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Mar. 31, 2014
Property, Plant and Equipment [Line Items]        
Proceeds from sale of properties $ 324,852us-gaap_ProceedsFromSaleOfOilAndGasPropertyAndEquipment      
Gain on sale of properties 186,999us-gaap_GainLossOnSaleOfProperty 0us-gaap_GainLossOnSaleOfProperty 0us-gaap_GainLossOnSaleOfProperty  
Oil and gas properties   191,384oas_AssetsHeldforSaleOilandGasProperties    
Less: accumulated depreciation, depletion, amortization and impairment   (54,318)oas_AssetsHeldforSaleAccumulatedDepreciationDepletionAmortizationandImpairment    
Total assets 0us-gaap_DisposalGroupIncludingDiscontinuedOperationLongLivedAssets 137,066us-gaap_DisposalGroupIncludingDiscontinuedOperationLongLivedAssets    
Asset retirement obligation   1,973oas_LiabilitiesofAssetsHeldforSaleAssetRetirementObligation    
Total liabilities   1,973us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperation    
Net assets   135,093oas_AssetsHeldforSaleLongLivedNetofLiabilities    
Non-Operated OIl and Natural Gas Properties [Member]        
Property, Plant and Equipment [Line Items]        
Proceeds from sale of properties       324,900us-gaap_ProceedsFromSaleOfOilAndGasPropertyAndEquipment
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= oas_NonOperatedOIlandNaturalGasPropertiesMember
Gain on sale of properties       $ 187,000us-gaap_GainLossOnSaleOfProperty
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= oas_NonOperatedOIlandNaturalGasPropertiesMember