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Acquisitions - Allocation of Purchase Price (Details) (USD $) In Thousands, unless otherwise specified	0 Months Ended	12 Months Ended
	Sep. 26, 2013	Dec. 31, 2014
West Williston Acquisition [Member]
Business Combination, Consideration Transferred [Abstract]
Cash		$ 1,475,361us-gaap_PaymentsToAcquireBusinessesGross / us-gaap_BusinessAcquisitionAxis = oas_WestWillistonAcquisitionMember
Forgiveness of debt		0us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred / us-gaap_BusinessAcquisitionAxis = oas_WestWillistonAcquisitionMember
Total consideration		1,475,361us-gaap_BusinessCombinationConsiderationTransferred1 / us-gaap_BusinessAcquisitionAxis = oas_WestWillistonAcquisitionMember
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets [Abstract]
Proved developed properties		519,712oas_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedProvedDevelopedProperties / us-gaap_BusinessAcquisitionAxis = oas_WestWillistonAcquisitionMember
Proved undeveloped properties		165,907oas_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedProvedUndevelopedProperties / us-gaap_BusinessAcquisitionAxis = oas_WestWillistonAcquisitionMember
Unproved lease acquisition costs		787,589oas_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedUnprovedLeaseAcquisitionCosts / us-gaap_BusinessAcquisitionAxis = oas_WestWillistonAcquisitionMember
Other property and equipment		13,157oas_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedOtherPropertyandEquipment / us-gaap_BusinessAcquisitionAxis = oas_WestWillistonAcquisitionMember
Inventory		3,181us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory / us-gaap_BusinessAcquisitionAxis = oas_WestWillistonAcquisitionMember
Accounts receivable		276us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables / us-gaap_BusinessAcquisitionAxis = oas_WestWillistonAcquisitionMember
Total assets acquired		1,489,822us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets / us-gaap_BusinessAcquisitionAxis = oas_WestWillistonAcquisitionMember
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities [Abstract]
Asset retirement obligations		6,598us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther / us-gaap_BusinessAcquisitionAxis = oas_WestWillistonAcquisitionMember
Revenues payable		7,863us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesOther / us-gaap_BusinessAcquisitionAxis = oas_WestWillistonAcquisitionMember
Total liabilities assumed		14,461us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities / us-gaap_BusinessAcquisitionAxis = oas_WestWillistonAcquisitionMember
Total identifiable net assets		1,475,361us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = oas_WestWillistonAcquisitionMember
East Nesson [Member]
Business Combination, Consideration Transferred [Abstract]
Cash		56,793us-gaap_PaymentsToAcquireBusinessesGross / us-gaap_BusinessAcquisitionAxis = oas_EastNessonMember
Forgiveness of debt		(43)us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred / us-gaap_BusinessAcquisitionAxis = oas_EastNessonMember
Total consideration	56,800us-gaap_BusinessCombinationConsiderationTransferred1 / us-gaap_BusinessAcquisitionAxis = oas_EastNessonMember	56,750us-gaap_BusinessCombinationConsiderationTransferred1 / us-gaap_BusinessAcquisitionAxis = oas_EastNessonMember
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets [Abstract]
Proved developed properties		32,053oas_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedProvedDevelopedProperties / us-gaap_BusinessAcquisitionAxis = oas_EastNessonMember
Proved undeveloped properties		1,807oas_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedProvedUndevelopedProperties / us-gaap_BusinessAcquisitionAxis = oas_EastNessonMember
Unproved lease acquisition costs		23,369oas_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedUnprovedLeaseAcquisitionCosts / us-gaap_BusinessAcquisitionAxis = oas_EastNessonMember
Other property and equipment		0oas_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedOtherPropertyandEquipment / us-gaap_BusinessAcquisitionAxis = oas_EastNessonMember
Inventory		148us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory / us-gaap_BusinessAcquisitionAxis = oas_EastNessonMember
Accounts receivable		0us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables / us-gaap_BusinessAcquisitionAxis = oas_EastNessonMember
Total assets acquired		57,377us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets / us-gaap_BusinessAcquisitionAxis = oas_EastNessonMember
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities [Abstract]
Asset retirement obligations		307us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther / us-gaap_BusinessAcquisitionAxis = oas_EastNessonMember
Revenues payable		320us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesOther / us-gaap_BusinessAcquisitionAxis = oas_EastNessonMember
Total liabilities assumed		627us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities / us-gaap_BusinessAcquisitionAxis = oas_EastNessonMember
Total identifiable net assets		$ 56,750us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = oas_EastNessonMember

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Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Property and Equipment

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