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Property, Plant and Equipment - Additional Information (Detail) (USD $) | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Property, Plant and Equipment [Line Items] |  |  |
Asset retirement costs | $ 36,900,000 us-gaap_CapitalizedCostsAssetRetirementCosts | $ 32,600,000 us-gaap_CapitalizedCostsAssetRetirementCosts |
Impairment of oil and gas properties | 47,238,000 us-gaap_ImpairmentOfOilAndGasProperties | 1,168,000 us-gaap_ImpairmentOfOilAndGasProperties | 3,581,000 us-gaap_ImpairmentOfOilAndGasProperties
Proved oil and gas properties [Member] |  |  |
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] |  |  |
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

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- Definition The amount of asset retirement costs previously incurred and capitalized separately from the capitalized amount of the associated long-lived assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e61901-109447 + Details
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- Definition The expense recorded to reduce the value of oil and gas assets consisting of proved properties and unproved properties as the estimate of future successful production from these properties is reduced. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 360 -Section 35 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=28370743&loc=d3e66150-109466 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6391110&loc=d3e2921-110230 + Details
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- Details
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