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Long-Term Debt (Schedule Of Long-Term Debt Interest Rate) (Details) | 12 Months Ended
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Dec. 31, 2011
Less Than .25 To 1 [Member] | Maximum [Member] |
Debt Instrument [Line Items] |
Ratio of total outstanding borrowings to borrowing Base | 0.25
Greater Than Or Equal To .25 To 1 But Less Than .50 To 1 [Member] | Maximum [Member] |
Debt Instrument [Line Items] |
Ratio of total outstanding borrowings to borrowing Base | 0.50
Greater Than Or Equal To .25 To 1 But Less Than .50 To 1 [Member] | Minimum [Member] |
Debt Instrument [Line Items] |
Ratio of total outstanding borrowings to borrowing Base | 0.25
Greater Than Or Equal To .50 To 1 But Less Than .75 To 1 [Member] | Maximum [Member] |
Debt Instrument [Line Items] |
Ratio of total outstanding borrowings to borrowing Base | 0.75
Greater Than Or Equal To .50 To 1 But Less Than .75 To 1 [Member] | Minimum [Member] |
Debt Instrument [Line Items] |
Ratio of total outstanding borrowings to borrowing Base | 0.50
Greater Than Or Equal To .75 To 1 But Less Than .90 To 1 [Member] | Maximum [Member] |
Debt Instrument [Line Items] |
Ratio of total outstanding borrowings to borrowing Base | 0.90
Greater Than Or Equal To .75 To 1 But Less Than .90 To 1 [Member] | Minimum [Member] |
Debt Instrument [Line Items] |
Ratio of total outstanding borrowings to borrowing Base | 0.75
Greater Than .90 To 1 But Less Than Or Equal 1 [Member] | Minimum [Member] |
Debt Instrument [Line Items] |
Ratio of total outstanding borrowings to borrowing Base | 0.90
LIBOR [Member] | Less Than .25 To 1 [Member] |
Debt Instrument [Line Items] |
Debt instrument interest rate terms, in percentage | 1.50%
LIBOR [Member] | Greater Than Or Equal To .25 To 1 But Less Than .50 To 1 [Member] |
Debt Instrument [Line Items] |
Debt instrument interest rate terms, in percentage | 1.75%
LIBOR [Member] | Greater Than Or Equal To .50 To 1 But Less Than .75 To 1 [Member] |
Debt Instrument [Line Items] |
Debt instrument interest rate terms, in percentage | 2.00%
LIBOR [Member] | Greater Than Or Equal To .75 To 1 But Less Than .90 To 1 [Member] |
Debt Instrument [Line Items] |
Debt instrument interest rate terms, in percentage | 2.25%
LIBOR [Member] | Greater Than .90 To 1 But Less Than Or Equal 1 [Member] |
Debt Instrument [Line Items] |
Debt instrument interest rate terms, in percentage | 2.50%
ABR [Member] | Less Than .25 To 1 [Member] |
Debt Instrument [Line Items] |
Debt instrument interest rate terms, in percentage | 0.00%
ABR [Member] | Greater Than Or Equal To .25 To 1 But Less Than .50 To 1 [Member] |
Debt Instrument [Line Items] |
Debt instrument interest rate terms, in percentage | 0.25%
ABR [Member] | Greater Than Or Equal To .50 To 1 But Less Than .75 To 1 [Member] |
Debt Instrument [Line Items] |
Debt instrument interest rate terms, in percentage | 0.50%
ABR [Member] | Greater Than Or Equal To .75 To 1 But Less Than .90 To 1 [Member] |
Debt Instrument [Line Items] |
Debt instrument interest rate terms, in percentage | 0.75%
ABR [Member] | Greater Than .90 To 1 But Less Than Or Equal 1 [Member] |
Debt Instrument [Line Items] |
Debt instrument interest rate terms, in percentage | 1.00%

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- Definition Ratio of total outstanding borrowings to borrowing base, numerator. + References No definition available. + Details
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Namespace Prefix: | oas_
Data Type: | xbrli:pureItemType
Balance Type: | na
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- Details
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Period Type: | duration

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- Definition The effective interest rate during the reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 22 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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