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Supplemental Oil and Gas Disclosures - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Proved oil and gas properties
Oil and Gas Delivery Commitments and Contracts [Line Items]
Asset retirement costs	$ 40.5	$ 38.4

X

- Definition

The amount of asset retirement costs previously incurred and capitalized separately from the capitalized amount of the associated long-lived assets.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 235
-Section 50
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e61901-109447

+ Details

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Balance Type:	debit
Period Type:	instant

X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_OilAndGasDeliveryCommitmentsAndContractsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=oas_ProvedOilAndGasPropertiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: