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Derivative Instruments - Schedule of Outstanding Commodity Derivative Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015
Derivative [Line Items]
Fair Value Asset (Liability)	$ 253,320us-gaap_DerivativeFairValueOfDerivativeNet
2015 Two-Way Collars [Member]
Derivative [Line Items]
Total Notional Amount of Oil (Barrels)	1,402invest_DerivativeNonmonetaryNotionalAmount / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = oas_TwoThousandFifteenTwoWayCollarsMember
Average Floor Price (in dollars per barrel)	86.52us-gaap_DerivativeAverageFloorPrice / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = oas_TwoThousandFifteenTwoWayCollarsMember
Average Ceiling Price (in dollars per barrel)	102.86us-gaap_DerivativeAverageCapPrice / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = oas_TwoThousandFifteenTwoWayCollarsMember
Fair Value Asset (Liability)	57,100us-gaap_DerivativeFairValueOfDerivativeNet / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = oas_TwoThousandFifteenTwoWayCollarsMember
2015 Swaps [Member]
Derivative [Line Items]
Total Notional Amount of Oil (Barrels)	3,381invest_DerivativeNonmonetaryNotionalAmount / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = oas_TwoThousandFifteenSwapContractsMember
Average Swap Price (in dollars per barrel)	89.36us-gaap_DerivativeSwapTypeAverageFixedPrice / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = oas_TwoThousandFifteenSwapContractsMember
Fair Value Asset (Liability)	152,359us-gaap_DerivativeFairValueOfDerivativeNet / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = oas_TwoThousandFifteenSwapContractsMember
2015 Deferred Premium Puts [Member]
Derivative [Line Items]
Total Notional Amount of Oil (Barrels)	546invest_DerivativeNonmonetaryNotionalAmount / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = oas_TwoThousandFifteenDeferredPremiumPutsMember
Average Floor Price (in dollars per barrel)	90.00us-gaap_DerivativeAverageFloorPrice / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = oas_TwoThousandFifteenDeferredPremiumPutsMember
Average deferred premium (in dollars per barrel)	2.55oas_DerivativeAverageDeferredPremium / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = oas_TwoThousandFifteenDeferredPremiumPutsMember
Fair Value Asset (Liability)	28,188us-gaap_DerivativeFairValueOfDerivativeNet / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = oas_TwoThousandFifteenDeferredPremiumPutsMember
2016 Two Way Collars [Member]
Derivative [Line Items]
Total Notional Amount of Oil (Barrels)	155invest_DerivativeNonmonetaryNotionalAmount / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = oas_TwoThousandSixteenTwoWayCollarsMember
Average Floor Price (in dollars per barrel)	86.00us-gaap_DerivativeAverageFloorPrice / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = oas_TwoThousandSixteenTwoWayCollarsMember
Average Ceiling Price (in dollars per barrel)	103.42us-gaap_DerivativeAverageCapPrice / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = oas_TwoThousandSixteenTwoWayCollarsMember
Fair Value Asset (Liability)	4,717us-gaap_DerivativeFairValueOfDerivativeNet / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = oas_TwoThousandSixteenTwoWayCollarsMember
2016 Swaps [Member]
Derivative [Line Items]
Total Notional Amount of Oil (Barrels)	372invest_DerivativeNonmonetaryNotionalAmount / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = oas_TwoThousandSixteenSwapsMember
Average Swap Price (in dollars per barrel)	85.27us-gaap_DerivativeSwapTypeAverageFixedPrice / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = oas_TwoThousandSixteenSwapsMember
Fair Value Asset (Liability)	$ 10,956us-gaap_DerivativeFairValueOfDerivativeNet / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = oas_TwoThousandSixteenSwapsMember

X

- Definition

Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 12

-Section 13

-Sentence Column B

+ Details

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- Definition

DerivativeAverageDeferredPremium

+ References

No definition available.

+ Details

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X

- Definition

The average cap rate on a group of price risk derivatives such as caps or collars. A payment or receipt is triggered if the market rate exceeds the cap rate on the contract.

+ References

No definition available.

+ Details

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X

- Definition

The average floor rate on a group of price risk derivatives such as floors or collars. A payment or receipt is triggered if the market rate falls below the floor rate on the contract.

+ References

No definition available.

+ Details

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X

- Definition

Fair value of the assets less the liabilities of a derivative or group of derivatives.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 10

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=49121117&loc=d3e13433-108611



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 15

-URI http://asc.fasb.org/extlink&oid=49121117&loc=d3e13495-108611



Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 6

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	debit
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- Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Average fixed price related to the group of price risk swap derivatives.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
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- Details

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- Details

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