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v2.4.0.6

Consolidating Financial Statements - Additional Information (Detail) | 12 Months Ended
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Dec. 31, 2012
Condensed Financial Information [Line Items] |
Ownership percentage, Guarantors | 100.00%

X
- Details
Name: | oas_CondensedFinancialInformationLineItems
Namespace Prefix: | oas_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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