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Supplemental Oil and Gas Reserve Information - Unaudited - Additional Information (Detail)	1 Months Ended	12 Months Ended
	Mar. 31, 2014 MBoe	Dec. 31, 2014 MBbls MBoe	Dec. 31, 2013 MBbls	Dec. 31, 2012 MBoe MMcf
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Purchases of Minerals in Place (Energy)		1,799us-gaap_ProvedDevelopedAndUndevelopedReservePurchaseOfMineralInPlaceEnergy	45,731us-gaap_ProvedDevelopedAndUndevelopedReservePurchaseOfMineralInPlaceEnergy	966us-gaap_ProvedDevelopedAndUndevelopedReservePurchaseOfMineralInPlaceEnergy
Proved Developed and Undeveloped Reserves, Extensions, Discoveries, and Additions (Energy)		92,596us-gaap_ProvedDevelopedAndUndevelopedReserveExtensionAndDiscoveryEnergy	46,094us-gaap_ProvedDevelopedAndUndevelopedReserveExtensionAndDiscoveryEnergy	73,871us-gaap_ProvedDevelopedAndUndevelopedReserveExtensionAndDiscoveryEnergy
Estimated extensions and discoveries of reserves associated with new wells		34,404oas_EstimatedExtensionsAndDiscoveriesOfReservesAssociatedWithNewWells	22,190oas_EstimatedExtensionsAndDiscoveriesOfReservesAssociatedWithNewWells	16,548oas_EstimatedExtensionsAndDiscoveriesOfReservesAssociatedWithNewWells
Additional proved undeveloped reserves		58,192oas_AdditionalProvedUndevelopedReserves	23,904oas_AdditionalProvedUndevelopedReserves	57,323oas_AdditionalProvedUndevelopedReserves
Percentage of reserves produced from wells in certain formations		100.00%oas_PercentageOfReservesProducedFromWells	100.00%oas_PercentageOfReservesProducedFromWells	100.00%oas_PercentageOfReservesProducedFromWells
Percentage of proved undeveloped reserves		100.00%oas_PercentageOfProvedUndevelopedReserves	100.00%oas_PercentageOfProvedUndevelopedReserves	100.00%oas_PercentageOfProvedUndevelopedReserves
Proved Developed and Undeveloped Reserves, Sales of Minerals in Place (Energy)	(8,448)us-gaap_ProvedDevelopedAndUndevelopedReservesSaleOfMineralInPlaceEnergy	(8,448)us-gaap_ProvedDevelopedAndUndevelopedReservesSaleOfMineralInPlaceEnergy	0us-gaap_ProvedDevelopedAndUndevelopedReservesSaleOfMineralInPlaceEnergy	0us-gaap_ProvedDevelopedAndUndevelopedReservesSaleOfMineralInPlaceEnergy
Reserves divested associated with non-operated properties sold		7,640us-gaap_ProvedDevelopedAndUndevelopedReservesSalesOfMineralsInPlace	0us-gaap_ProvedDevelopedAndUndevelopedReservesSalesOfMineralsInPlace	0us-gaap_ProvedDevelopedAndUndevelopedReservesSalesOfMineralsInPlace
Net positive (negative) revisions of previous estimates		(25,117)us-gaap_ProvedDevelopedAndUndevelopedReserveRevisionOfPreviousEstimateEnergy	5,125us-gaap_ProvedDevelopedAndUndevelopedReserveRevisionOfPreviousEstimateEnergy	(1,983)us-gaap_ProvedDevelopedAndUndevelopedReserveRevisionOfPreviousEstimateEnergy
Percentage of net positive (negative) revisions		(11.00%)oas_RevisionsPercentage	3.60%oas_RevisionsPercentage	(2.50%)oas_RevisionsPercentage
Proved Undeveloped Reserves, Number of Locations		80oas_ProvedUndevelopedReservesNumberofLocations
Proved Undeveloped Reserves, Number of Locations, Net		56.2oas_ProvedUndevelopedReservesNumberofLocationsNet
Proved Undeveloped Reserves, Decrease from Estimated Net Proved Reserve Balance (Energy)		21,411oas_ProvedUndevelopedReservesDecreasefromEstimatedNetProvedReserveBalanceEnergy
Discount rate of future cash flows		10.00%oas_DiscountRateOfFutureCashFlows
Unweighted arithmetic average first-day-of-the-month prices for oil, price per Bbl		95.28oas_UnweightedArithmeticAverageFirstDayOfMonthPrices	96.96oas_UnweightedArithmeticAverageFirstDayOfMonthPrices	94.68oas_UnweightedArithmeticAverageFirstDayOfMonthPrices
Unweighted arithmetic average first-day-of-the-month prices for natural gas, price per MMBtu		4.35oas_UnweightedArithmeticAverageFirstDayOfMonthPricesForNaturalGas	3.66oas_UnweightedArithmeticAverageFirstDayOfMonthPricesForNaturalGas	2.75oas_UnweightedArithmeticAverageFirstDayOfMonthPricesForNaturalGas
Burke and Mountrail counties [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Purchases of Minerals in Place (Energy)				966us-gaap_ProvedDevelopedAndUndevelopedReservePurchaseOfMineralInPlaceEnergy / us-gaap_StatementGeographicalAxis = oas_BurkeAndMountrailCountyMember

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Additional proved undeveloped reserves

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Estimated extensions and discoveries of reserves associated with new wells

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Proved Undeveloped Reserves, Decrease from Estimated Net Proved Reserve Balance (Energy)

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Revisions as a percentage of beginning of the years reserves balance.

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Unweighted arithmetic average first-day-of-the-month prices for natural gas

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Energy measure of increase in quantity of proved reserve of oil and gas resulting from the extension of the proved acreage of previously discovered reservoir or discovery of new field with proved reserve or of new reservoir of proved reserve in old field, stated in a unit of energy. For example, but not limited to, barrel of oil equivalents (BOE) or one thousand cubic feet of natural gas equivalent (Mcfe).

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