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Commitments and Contingencies - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Commitments And Contingencies [Line Items]
Total rental commitments under leases	$ 32,500,000us-gaap_OperatingLeasesFutureMinimumPaymentsDue
Rig termination	1,080,000oas_OilandGasRigTerminationExpense	0oas_OilandGasRigTerminationExpense
Future obligations under purchase agreements	52,800,000oas_FutureObligationsUnderPurchaseAgreements
Future obligations under cost sharing agreements	8,100,000oas_FutureObligationsUnderCostSharingAgreements
Long Term Commitments [Member]
Commitments And Contingencies [Line Items]
Future obligations under supply agreements	190,500,000oas_FutureObligationsUnderSupplyAgreements / us-gaap_SupplyCommitmentAxis = oas_LongTermCommitmentsMember
Drilling contracts [Member]
Commitments And Contingencies [Line Items]
Rig termination	1,100,000oas_OilandGasRigTerminationExpense / us-gaap_LossContingenciesByNatureOfContingencyAxis = oas_DrillingContractsMember
Payments upon early contract termination	$ 10,200,000us-gaap_LossContingencyEstimateOfPossibleLoss / us-gaap_LossContingenciesByNatureOfContingencyAxis = oas_DrillingContractsMember
Williston Basin Project [Member] | Long Term Commitments [Member]
Commitments And Contingencies [Line Items]
Maximum commitment term	10 years
Williston Basin Project [Member] | Long Term Commitments [Member] | Crude oil [Member]
Commitments And Contingencies [Line Items]
Minimum quantity of delivery	31,000us-gaap_OilAndGasDeliveryCommitmentsAndContractsRemainingContractualVolume / us-gaap_EnergyAxis = us-gaap_CrudeOilMember / us-gaap_ProductOrServiceAxis = oas_WillistonBasinProjectMember / us-gaap_SupplyCommitmentAxis = oas_LongTermCommitmentsMember
Williston Basin Project [Member] | Long Term Commitments [Member] | Natural Gas [Member]
Commitments And Contingencies [Line Items]
Minimum quantity of delivery	6,600us-gaap_OilAndGasDeliveryCommitmentsAndContractsRemainingContractualVolume / us-gaap_EnergyAxis = us-gaap_NaturalGasReservesMember / us-gaap_ProductOrServiceAxis = oas_WillistonBasinProjectMember / us-gaap_SupplyCommitmentAxis = oas_LongTermCommitmentsMember

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- Definition

Future Obligations Under Cost Sharing Agreements

+ References

No definition available.

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- Definition

Future Obligations Under Purchase Agreements

+ References

No definition available.

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- Definition

Future obligations under supply agreements

+ References

No definition available.

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- Definition

The maximum duration period applicable to the existing commitments.

+ References

No definition available.

+ Details

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- Definition

Oil and Gas, Rig Termination Expense

+ References

No definition available.

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- Definition

Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 4

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14435-108349



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 9

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14557-108349

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- Definition

Total amount of product committed to be supplied under existing contracts or agreements.

+ References

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

-Publisher SEC

-Name Regulation S-K (SK)

-Number 229

-Section 1207

-Paragraph (a)

-Subparagraph (2)

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- Definition

Amount of required minimum rental payments for leases having an initial or remaining non-cancelable letter-terms in excess of one year.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 10

-Section 55

-Paragraph 40

-Subparagraph (Note 3)

-URI http://asc.fasb.org/extlink&oid=6584154&loc=d3e38371-112697



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-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 20

-Section 50

-Paragraph 2

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6453985&loc=d3e41502-112717

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