The realized gain (loss) on commodity derivatives relating to actual amounts received or paid under the respective contracts and the unrealized gain or loss on commodity derivative contracts representing the change in the fair market value of derivative instruments that have not actually settled.

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Actual amounts received or paid related to derivative instruments, including options, swaps, futures, and forward contracts, which were included in earnings in the period.

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Fair value of derivative asset, 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 Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4B

-Subparagraph (a),(c)

-URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5624163-113959

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

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

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Reference to the index or unit of measurement for the underlying which establishes the pricing terms of the derivative instrument. For example, the basis on the underlying for a natural gas futures contract might be the NYMEX price per million British thermal units (MMBtu).

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- Definition

The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 28

-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 Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3602-108585

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Derivative Financial Instruments (Details) (USD $)	3 Months Ended		9 Months Ended
Derivative Financial Instruments (Details) (USD $)	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Natural Gas Commodity Derivatives [Abstract]
Realized (loss) gain on commodity derivatives	$ 53,630,000	$ 40,583,000	$ 143,749,000	$ 77,568,000
Unrealized Gain (Loss) on Derivatives	60,536,000	109,603,000	33,658,000	268,535,000
Gain loss on commodity derivatives	114,166,000	150,186,000	177,407,000	346,103,000
Swap [Member] \| N W Rockies [Member] \| Calendar 2011 [Member]
Schedule Of Derivative Instruments [Line Items]
Derivative, Underlying Basis			170,000
Derivative, Swap Type, Average Fixed Price	5.08		5.08
Derivative Asset, Fair Value	21,611,000		21,611,000
Swap [Member] \| Northeast [Member] \| Calendar 2011 [Member]
Schedule Of Derivative Instruments [Line Items]
Derivative, Underlying Basis			195,000
Derivative, Swap Type, Average Fixed Price	5.81		5.81
Derivative Asset, Fair Value	34,305,000		34,305,000
Swap [Member] \| Nymex [Member] \| Calendar 2012 [Member]
Schedule Of Derivative Instruments [Line Items]
Derivative, Underlying Basis			300,000
Derivative, Swap Type, Average Fixed Price	5.03		5.03
Derivative Asset, Fair Value	86,311,000		86,311,000
Swap [Member] \| Nymex [Member] \| Summer 2011 [Member]
Schedule Of Derivative Instruments [Line Items]
Derivative, Underlying Basis			230,000
Derivative, Swap Type, Average Fixed Price	4.58		4.58
Derivative Asset, Fair Value	5,875,000		5,875,000
Swap [Member] \| Nymex [Member] \| Summer 2012 [Member]
Schedule Of Derivative Instruments [Line Items]
Derivative, Underlying Basis			90,000
Derivative, Swap Type, Average Fixed Price	5.00		5.00
Derivative Asset, Fair Value	$ 15,557,000		$ 15,557,000