Derivative Financial Instruments (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Natural Gas Commodity Derivatives [Abstract]
Realized (loss) gain on commodity derivatives	$ 45,080,000	$ 37,654,000	$ 90,120,000	$ 36,985,000
Unrealized Gain (Loss) on Derivatives	2,526,000	(23,088,000)	(26,879,000)	158,932,000
Gain loss on commodity derivatives	47,606,000	14,566,000	63,241,000	195,917,000
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	26,980,000		26,980,000
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	44,294,000		44,294,000
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	21,644,000		21,644,000
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	5,538,000		5,538,000
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	$ 4,668,000		$ 4,668,000