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Condensed Consolidating Financial Information - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2013
Condensed Financial Information Of Parent Company Only Disclosure [Abstract]
Ownership percentage, Guarantors	100.00%

X

- Definition

Ownership percentage, guarantor

+ References

No definition available.

+ Details

Name:	oas_OwnershipPercentageGuarantor
Namespace Prefix:	oas_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Details

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