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Commitments and Contingencies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Commitments And Contingencies [Line Items]
Rental expense	$ 2.0us-gaap_OperatingLeasesRentExpenseNet	$ 1.6us-gaap_OperatingLeasesRentExpenseNet	$ 1.5us-gaap_OperatingLeasesRentExpenseNet
Future Obligations Under Cost Sharing Agreements	9.0oas_FutureObligationsUnderCostSharingAgreements
Capital spending commitment	4.8oas_CapitalSpendingCommitment
Long Term Commitments [Member]
Commitments And Contingencies [Line Items]
Supply Commitment, Maximum Term	10 years
Future obligations under supply agreements	194.0oas_FutureObligationsUnderSupplyAgreements / us-gaap_SupplyCommitmentAxis = oas_LongTermCommitmentsMember
Long Term Commitments [Member] | Williston Basin Project [Member] | Crude oil collar [Member]
Commitments And Contingencies [Line Items]
Minimum quantity of delivery	31,700us-gaap_OilAndGasDeliveryCommitmentsAndContractsRemainingContractualVolume / us-gaap_EnergyAxis = us-gaap_CrudeOilMember / us-gaap_ProductOrServiceAxis = oas_WillistonBasinProjectMember / us-gaap_SupplyCommitmentAxis = oas_LongTermCommitmentsMember
Long Term Commitments [Member] | Williston Basin Project [Member] | Natural Gas [Member]
Commitments And Contingencies [Line Items]
Minimum quantity of delivery	7,900us-gaap_OilAndGasDeliveryCommitmentsAndContractsRemainingContractualVolume / us-gaap_EnergyAxis = us-gaap_NaturalGasReservesMember / us-gaap_ProductOrServiceAxis = oas_WillistonBasinProjectMember / us-gaap_SupplyCommitmentAxis = oas_LongTermCommitmentsMember
Drilling contracts [Member]
Commitments And Contingencies [Line Items]
Payments upon early contract termination	15.0us-gaap_LossOnContractTermination / us-gaap_LossContingenciesByNatureOfContingencyAxis = oas_DrillingContractsMember
Well Completion Services Equipment and Fresh Water [Member]
Commitments And Contingencies [Line Items]
Long-term Purchase Commitment, Amount	$ 20.0us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = oas_WellCompletionServicesEquipmentandFreshWaterMember

X

- Definition

Capital Spending Commitment

+ References

No definition available.

+ Details

Name:	oas_CapitalSpendingCommitment
Namespace Prefix:	oas_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Details

Name:	oas_CommitmentsAndContingenciesLineItems
Namespace Prefix:	oas_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Future Obligations Under Cost Sharing Agreements

+ References

No definition available.

+ Details

Name:	oas_FutureObligationsUnderCostSharingAgreements
Namespace Prefix:	oas_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Future obligations under supply agreements

+ References

No definition available.

+ Details

Name:	oas_FutureObligationsUnderSupplyAgreements
Namespace Prefix:	oas_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Supply Commitment, Maximum Term

+ References

No definition available.

+ Details

Name:	oas_SupplyCommitmentMaximumTerm
Namespace Prefix:	oas_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The minimum amount the entity agreed to spend under the long-term purchase commitment.

+ References

No definition available.

+ Details

Name:	us-gaap_LongTermPurchaseCommitmentAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

The loss recognized on termination of a contract.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 912

-SubTopic 275

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=6471736&loc=d3e54681-109401

+ Details

Name:	us-gaap_LossOnContractTermination
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- 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 Industry Guide

-Number 2

-Paragraph 8

-Subparagraph A

+ Details

Name:	us-gaap_OilAndGasDeliveryCommitmentsAndContractsRemainingContractualVolume
Namespace Prefix:	us-gaap_
Data Type:	num:volumeItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Rental expense for the reporting period incurred under operating leases, including minimum and any contingent rent expense, net of related sublease income.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6453985&loc=d3e41499-112717

+ Details

Name:	us-gaap_OperatingLeasesRentExpenseNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Details

Name:	us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis=oas_WellCompletionServicesEquipmentandFreshWaterMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_LossContingenciesByNatureOfContingencyAxis=oas_DrillingContractsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_SupplyCommitmentAxis=oas_LongTermCommitmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: