Derivative Activities (Details 2) (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Derivative assets:
Derivative Assets - Commodity collars, swaps, basis swaps and call options	$ 183,609	$ 131,450
Derivative liabilities:
Derivative Liabilities - Commodity collars, swaps, basis swaps and call options	0	(13,764)
Crude Oil [Member] | Collars [Member]
Derivative assets:
Derivative Assets - Commodity collars, swaps, basis swaps and call options	(4,340)	0
Derivative liabilities:
Derivative Liabilities - Commodity collars, swaps, basis swaps and call options	0	(12,051)
Crude Oil [Member] | Call Option [Member]
Derivative assets:
Derivative Assets - Commodity collars, swaps, basis swaps and call options	(20,737)	(31,904)
Derivative liabilities:
Derivative Liabilities - Commodity collars, swaps, basis swaps and call options	0	(28,393)
NGL [Member] | Swap [Member]
Derivative assets:
Derivative Assets - Commodity collars, swaps, basis swaps and call options	36,881	0
Derivative liabilities:
Derivative Liabilities - Commodity collars, swaps, basis swaps and call options	0	0
Natural Gas [Member] | Swap [Member]
Derivative assets:
Derivative Assets - Commodity collars, swaps, basis swaps and call options	19,304	0
Derivative liabilities:
Derivative Liabilities - Commodity collars, swaps, basis swaps and call options	0	0
Natural Gas [Member] | Basis Swap [Member]
Derivative liabilities:
Derivative Liabilities - Commodity collars, swaps, basis swaps and call options	0	(352)
Natural Gas [Member] | Collars [Member]
Derivative assets:
Derivative Assets - Commodity collars, swaps, basis swaps and call options	152,501	155,159
Derivative liabilities:
Derivative Liabilities - Commodity collars, swaps, basis swaps and call options	0	27,032
Natural Gas [Member] | Collars discontinued operations [Member]
Derivative assets:
Derivative Assets - Commodity collars, swaps, basis swaps and call options	$ 0	$ 8,195