Derivative Activities (Details 5) (USD $) In Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Effects of non-hedge derivatives on consolidated statement of operations
Gain (Loss) Recognized in Income (Non-hedge Derivatives)	$ 45,529	$ 6,281	$ 3,181	$ 49,220
Gain Recognized in Income (Ineffective Portion)	7,510	265	9,024	(341)
Derivative fair value (loss) income	53,039	6,546	12,205	48,879
Collars [Member]
Effects of non-hedge derivatives on consolidated statement of operations
Gain (Loss) Recognized in Income (Non-hedge Derivatives)	6,452	1,483	(1,135)	48,438
Gain Recognized in Income (Ineffective Portion)	7,510	265	9,024	(341)
Derivative fair value (loss) income	13,962	1,748	7,889	48,097
Swap [Member]
Effects of non-hedge derivatives on consolidated statement of operations
Gain (Loss) Recognized in Income (Non-hedge Derivatives)	15,613	0	13,750	0
Gain Recognized in Income (Ineffective Portion)	0	0	0	0
Derivative fair value (loss) income	15,613	0	13,750	0
Basis Swap [Member]
Effects of non-hedge derivatives on consolidated statement of operations
Gain (Loss) Recognized in Income (Non-hedge Derivatives)	0	4,798	(43)	782
Gain Recognized in Income (Ineffective Portion)	0	0	0	0
Derivative fair value (loss) income	0	4,798	(43)	782
Call Option [Member]
Effects of non-hedge derivatives on consolidated statement of operations
Gain (Loss) Recognized in Income (Non-hedge Derivatives)	23,464	0	(9,391)	0
Gain Recognized in Income (Ineffective Portion)	0	0	0	0
Derivative fair value (loss) income	$ 23,464	$ 0	$ (9,391)	$ 0