Derivative Instruments (Schedule Of Outstanding Commodity Derivative Instruments) (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended
Jun. 30, 2012 bbl
Derivative Instruments [Line Items]
Fair Value Asset (Liability)	$ 53,424
2012 Two-Way Collars [Member]
Derivative Instruments [Line Items]
Total Notional Amount of Oil (Barrels)	1,189,500
Average Floor Price	89.23
Average Ceiling Price	108.76
Fair Value Asset (Liability)	7,906
Settlement Period	2012
2012 Three-Way Collars [Member]
Derivative Instruments [Line Items]
Total Notional Amount of Oil (Barrels)	1,860,000
Average Sub-Floor Price	66.39
Average Floor Price	90.33
Average Ceiling Price	109.70
Fair Value Asset (Liability)	12,093
Settlement Period	2012
2013 Two-Way Collars [Member]
Derivative Instruments [Line Items]
Total Notional Amount of Oil (Barrels)	201,500
Average Floor Price	89.23
Average Ceiling Price	108.76
Fair Value Asset (Liability)	1,533
Settlement Period	2013
2013 Three-Way Collars [Member]
Derivative Instruments [Line Items]
Total Notional Amount of Oil (Barrels)	2,023,420
Average Sub-Floor Price	65.30
Average Floor Price	92.51
Average Ceiling Price	112.63
Fair Value Asset (Liability)	13,978
Settlement Period	2013
2013 Put Spreads [Member]
Derivative Instruments [Line Items]
Total Notional Amount of Oil (Barrels)	1,717,080
Average Sub-Floor Price	70.71
Average Floor Price	91.24
Fair Value Asset (Liability)	12,853
Settlement Period	2013
2014 Three-Way Collars [Member]
Derivative Instruments [Line Items]
Total Notional Amount of Oil (Barrels)	827,030
Average Sub-Floor Price	71.08
Average Floor Price	92.58
Average Ceiling Price	114.15
Fair Value Asset (Liability)	3,714
Settlement Period	2014
2014 Put Spreads [Member]
Derivative Instruments [Line Items]
Total Notional Amount of Oil (Barrels)	150,970
Average Sub-Floor Price	71.03
Average Floor Price	91.03
Fair Value Asset (Liability)	1,104
Settlement Period	2014
2015 Three Way Collars [Member]
Derivative Instruments [Line Items]
Total Notional Amount of Oil (Barrels)	62,000
Average Sub-Floor Price	72.50
Average Floor Price	92.50
Average Ceiling Price	114.40
Fair Value Asset (Liability)	$ 243
Settlement Period	2015

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

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- Definition

The average strike price of the sold put that establishes the price at which if the market price falls below, the minimum price would be index price plus the difference between the purchased put (floor) and the sold put strike price.

+ References

No definition available.

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- Definition

Derivatives, Maturity Date

+ References

No definition available.

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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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- 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.

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- Definition

Fair value of the assets less the liabilities of a derivative or group of derivatives.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 6

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 10

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13433-108611

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 15

-URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13495-108611

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