Derivative Financial Instruments (Schedule of Derivative Liabilities at Fair Value) (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
Sep. 30, 2012 bbl
Swaps Oil [Member]
Derivatives, Fair Value [Line Items]
Notional Quantity (Bbls)	2,227,400
Weighted Average Contract Price	101.19
Fair Value Liability	$ 10,228
Swaps Oil [Member] \| 2012: 4th Quarter [Member]
Derivatives, Fair Value [Line Items]
Termination Period	4th quarter
Notional Quantity (Bbls)	257,600
Weighted Average Contract Price	107.28
Fair Value Liability	977
Swaps Oil [Member] \| 2013: 1st quarter [Member]
Derivatives, Fair Value [Line Items]
Termination Period	1st quarter
Notional Quantity (Bbls)	351,000
Weighted Average Contract Price	101.97
Fair Value Liability	2,501
Swaps Oil [Member] \| 2013: 2nd Quarter [Member]
Derivatives, Fair Value [Line Items]
Termination Period	2nd quarter
Notional Quantity (Bbls)	336,700
Weighted Average Contract Price	101.97
Fair Value Liability	1,862
Swaps Oil [Member] \| 2013: 3rd Quarter [Member]
Derivatives, Fair Value [Line Items]
Termination Period	3rd quarter
Notional Quantity (Bbls)	312,800
Weighted Average Contract Price	101.98
Fair Value Liability	1,265
Swaps Oil [Member] \| 2013: 4th Quarter [Member]
Derivatives, Fair Value [Line Items]
Termination Period	4th quarter
Notional Quantity (Bbls)	294,400
Weighted Average Contract Price	101.98
Fair Value Liability	805
Swaps Oil [Member] \| 2014: 1st Quarter [Member]
Derivatives, Fair Value [Line Items]
Termination Period	1st quarter
Notional Quantity (Bbls)	180,000
Weighted Average Contract Price	97.38
Fair Value Liability	1,073
Swaps Oil [Member] \| 2014: 2nd Quarter [Member]
Derivatives, Fair Value [Line Items]
Termination Period	2nd quarter
Notional Quantity (Bbls)	172,900
Weighted Average Contract Price	97.38
Fair Value Liability	807
Swaps Oil [Member] \| 2014: 3rd Quarter [Member]
Derivatives, Fair Value [Line Items]
Termination Period	3rd quarter
Notional Quantity (Bbls)	165,600
Weighted Average Contract Price	97.38
Fair Value Liability	573
Swaps Oil [Member] \| 2014: 4th Quarter [Member]
Derivatives, Fair Value [Line Items]
Termination Period	4th quarter
Notional Quantity (Bbls)	156,400
Weighted Average Contract Price	97.37
Fair Value Liability	365
Zero Cost Collars Oil [Member] \| 2012: 4th Quarter [Member]
Derivatives, Fair Value [Line Items]
Termination Period	4th quarter
Notional Quantity (Bbls)	251,000
Weighted Average Floor Contract Price	75.00
Weighted Average Ceiling Contract Price	98.99
Fair Value Liability	$ 345

Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 12

-Section 13

-Sentence Column B

+ Details

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- Definition

The average cap rate on a group of price risk derivatives such as caps or collars. A payment or receipt is triggered if the market rate exceeds the cap rate on the contract.

+ References

No definition available.

+ Details

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Period Type:	instant

- Definition

The average floor rate on a group of price risk derivatives such as floors or collars. A payment or receipt is triggered if the market rate falls below the floor rate on the contract.

+ References

No definition available.

+ Details

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- Definition

Description of the relevant terms of the derivative. Includes the type of instrument, risk being hedged, notional amount, counterparty, inception date, maturity date, relevant interest rates, strike price, cap price, and floor price.

+ References

No definition available.

+ Details

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- Definition

Fair value of derivative liability, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 205G

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 44C

-Subparagraph a

-Clause 1

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4B

-Subparagraph (a),(c)

-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624163-113959

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- Details

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- Definition

Average fixed price related to the group of price risk swap derivatives.

+ References

No definition available.

+ Details

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Data Type:	us-types:perUnitItemType
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Period Type:	instant