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Fair Value Measurements - Additional Information (Detail) (USD $) | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Debt Instrument [Line Items] |  |  |
Net derivative asset | $ (600,000)us-gaap_DerivativeCreditRiskValuationAdjustmentDerivativeAssets |  |
Derivative liability, net |  | 200,000 us-gaap_DerivativeCreditRiskValuationAdjustmentDerivativeLiabilities |
Long-term debt, carrying value | 2,700,000,000 us-gaap_LongTermDebtNoncurrent | 2,535,570,000 us-gaap_LongTermDebtNoncurrent |
Asset retirement obligation, carrying value | 42,549,000 us-gaap_AssetRetirementObligation | 36,458,000 us-gaap_AssetRetirementObligation | 23,234,000 us-gaap_AssetRetirementObligation
Impairment of oil and gas properties | 47,238,000 us-gaap_ImpairmentOfOilAndGasProperties | 1,168,000 us-gaap_ImpairmentOfOilAndGasProperties | 3,581,000 us-gaap_ImpairmentOfOilAndGasProperties
Senior unsecured notes [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term, unsecured notes and borrowings | 2,200,000,000 us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = oas_UnsecuredSeniorNotesMember |  |
Long-term debt, fair value | 2,020,000,000 us-gaap_LongTermDebtFairValue / us-gaap_DebtInstrumentAxis = oas_UnsecuredSeniorNotesMember |  |
Amended Credit Facility [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term, unsecured notes and borrowings | 500,000,000 us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = oas_AmendedCreditFacilityMember |  |
Proved oil and gas properties [Member] |  |  |
Debt Instrument [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
Reported Value Measurement [Member] | Proved oil and gas properties [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Fair value of property | 76,400,000 us-gaap_PropertyPlantAndEquipmentFairValueDisclosure / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember / us-gaap_PropertyPlantAndEquipmentByTypeAxis = oas_ProvedOilAndGasPropertiesMember |  |
Estimate of Fair Value Measurement [Member] | Proved oil and gas properties [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Fair value of property | $ 36,400,000 us-gaap_PropertyPlantAndEquipmentFairValueDisclosure / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember / us-gaap_PropertyPlantAndEquipmentByTypeAxis = oas_ProvedOilAndGasPropertiesMember |  |

X
- Definition The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Asset Retirement Obligation -URI http://asc.fasb.org/extlink&oid=6505190 + Details
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- Details
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- Definition Amount of credit risk valuation adjustment to derivative assets to properly reflect the credit quality of the counterparties. + References No definition available. + Details
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- Definition Amount of credit risk valuation adjustment to derivative liabilities to properly reflect the credit quality of the entity. + References No definition available. + 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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- Definition Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 16 -Article 7 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.16) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 16 -Article 9 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 20, 22 -Article 5 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.16) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 + Details
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- Definition The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. + References No definition available. + Details
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- Definition Carrying amount of long-term debt, net of unamortized discount or premium, excluding amounts to be repaid within one year or the normal operating cycle, if longer (current maturities). Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22 -Article 5 + Details
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- Definition Fair value portion of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19190-110258 + Details
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- Details
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Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |

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- Details
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