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Long-Term Debt - Schedule of Long-Term Debt Interest Rate (Detail)	12 Months Ended
	Dec. 31, 2014
Less than .25 to 1 [Member] | Maximum [Member]
Debt Instrument [Line Items]
Ratio of Total Outstanding Borrowings to Borrowing Base	0.25oas_RatioOfTotalOutstandingBorrowingsToBorrowingBase / us-gaap_CreditFacilityAxis = oas_LessThanPointTwoFiveToOneMember / us-gaap_RangeAxis = us-gaap_MaximumMember
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	0.50oas_RatioOfTotalOutstandingBorrowingsToBorrowingBase / us-gaap_CreditFacilityAxis = oas_GreaterThanOrEqualToPointTwoFiveToOneButLessThanPointFiveZeroToOneMember / us-gaap_RangeAxis = us-gaap_MaximumMember
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	0.25oas_RatioOfTotalOutstandingBorrowingsToBorrowingBase / us-gaap_CreditFacilityAxis = oas_GreaterThanOrEqualToPointTwoFiveToOneButLessThanPointFiveZeroToOneMember / us-gaap_RangeAxis = us-gaap_MinimumMember
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	0.75oas_RatioOfTotalOutstandingBorrowingsToBorrowingBase / us-gaap_CreditFacilityAxis = oas_GreaterThanOrEqualToPointFiveZeroToOneButLessThanPointSevenFiveToOneMember / us-gaap_RangeAxis = us-gaap_MaximumMember
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	0.50oas_RatioOfTotalOutstandingBorrowingsToBorrowingBase / us-gaap_CreditFacilityAxis = oas_GreaterThanOrEqualToPointFiveZeroToOneButLessThanPointSevenFiveToOneMember / us-gaap_RangeAxis = us-gaap_MinimumMember
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	0.90oas_RatioOfTotalOutstandingBorrowingsToBorrowingBase / us-gaap_CreditFacilityAxis = oas_GreaterThanOrEqualToPointSevenFiveToOneButLessThanPointNineZeroToOneMember / us-gaap_RangeAxis = us-gaap_MaximumMember
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	0.75oas_RatioOfTotalOutstandingBorrowingsToBorrowingBase / us-gaap_CreditFacilityAxis = oas_GreaterThanOrEqualToPointSevenFiveToOneButLessThanPointNineZeroToOneMember / us-gaap_RangeAxis = us-gaap_MinimumMember
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	0.90oas_RatioOfTotalOutstandingBorrowingsToBorrowingBase / us-gaap_CreditFacilityAxis = oas_GreaterThanPointNineGreaterThanPointNineZeroToOneButLessThanOrEqualOneMemberZeroToOneButLessThanOrEqualOneMember / us-gaap_RangeAxis = us-gaap_MinimumMember
LIBOR [Member] | Less than .25 to 1 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate terms, in percentage	1.50%us-gaap_LineOfCreditFacilityInterestRateDuringPeriod / us-gaap_CreditFacilityAxis = oas_LessThanPointTwoFiveToOneMember / us-gaap_DebtInstrumentAxis = us-gaap_LondonInterbankOfferedRateLIBORMember
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%us-gaap_LineOfCreditFacilityInterestRateDuringPeriod / us-gaap_CreditFacilityAxis = oas_GreaterThanOrEqualToPointTwoFiveToOneButLessThanPointFiveZeroToOneMember / us-gaap_DebtInstrumentAxis = us-gaap_LondonInterbankOfferedRateLIBORMember
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%us-gaap_LineOfCreditFacilityInterestRateDuringPeriod / us-gaap_CreditFacilityAxis = oas_GreaterThanOrEqualToPointFiveZeroToOneButLessThanPointSevenFiveToOneMember / us-gaap_DebtInstrumentAxis = us-gaap_LondonInterbankOfferedRateLIBORMember
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%us-gaap_LineOfCreditFacilityInterestRateDuringPeriod / us-gaap_CreditFacilityAxis = oas_GreaterThanOrEqualToPointSevenFiveToOneButLessThanPointNineZeroToOneMember / us-gaap_DebtInstrumentAxis = us-gaap_LondonInterbankOfferedRateLIBORMember
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%us-gaap_LineOfCreditFacilityInterestRateDuringPeriod / us-gaap_CreditFacilityAxis = oas_GreaterThanPointNineGreaterThanPointNineZeroToOneButLessThanOrEqualOneMemberZeroToOneButLessThanOrEqualOneMember / us-gaap_DebtInstrumentAxis = us-gaap_LondonInterbankOfferedRateLIBORMember
ABR [Member] | Less than .25 to 1 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate terms, in percentage	0.00%us-gaap_LineOfCreditFacilityInterestRateDuringPeriod / us-gaap_CreditFacilityAxis = oas_LessThanPointTwoFiveToOneMember / us-gaap_DebtInstrumentAxis = oas_AbrMember
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%us-gaap_LineOfCreditFacilityInterestRateDuringPeriod / us-gaap_CreditFacilityAxis = oas_GreaterThanOrEqualToPointTwoFiveToOneButLessThanPointFiveZeroToOneMember / us-gaap_DebtInstrumentAxis = oas_AbrMember
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%us-gaap_LineOfCreditFacilityInterestRateDuringPeriod / us-gaap_CreditFacilityAxis = oas_GreaterThanOrEqualToPointFiveZeroToOneButLessThanPointSevenFiveToOneMember / us-gaap_DebtInstrumentAxis = oas_AbrMember
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%us-gaap_LineOfCreditFacilityInterestRateDuringPeriod / us-gaap_CreditFacilityAxis = oas_GreaterThanOrEqualToPointSevenFiveToOneButLessThanPointNineZeroToOneMember / us-gaap_DebtInstrumentAxis = oas_AbrMember
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%us-gaap_LineOfCreditFacilityInterestRateDuringPeriod / us-gaap_CreditFacilityAxis = oas_GreaterThanPointNineGreaterThanPointNineZeroToOneButLessThanOrEqualOneMemberZeroToOneButLessThanOrEqualOneMember / us-gaap_DebtInstrumentAxis = oas_AbrMember

X

- Definition

Ratio of total outstanding borrowings to borrowing base.

+ References

No definition available.

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X

- Definition

The effective interest rate during the reporting period.

+ References

Reference 1: 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



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

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