Derivative Activities (Details 2) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Derivative assets:
Derivative Assets - Commodity swaps, collars, call and put options	$ 348,986	$ 251,500
Derivative liabilities:
Derivative Liabilities - Commodity swaps, collars, call and put options	(5,688)	(173)
Natural Gas [Member] | Swap [Member]
Derivative assets:
Derivative Assets - Commodity swaps, collars, call and put options	33,637	54,162
Derivative liabilities:
Derivative Liabilities - Commodity swaps, collars, call and put options	269
Natural Gas [Member] | Collars [Member]
Derivative assets:
Derivative Assets - Commodity swaps, collars, call and put options	208,178	228,228
Derivative liabilities:
Derivative Liabilities - Commodity swaps, collars, call and put options	(1,112)
Crude Oil [Member] | Swap [Member]
Derivative assets:
Derivative Assets - Commodity swaps, collars, call and put options	23,744	(263)
Crude Oil [Member] | Collars [Member]
Derivative assets:
Derivative Assets - Commodity swaps, collars, call and put options	5,254	(16,607)
Crude Oil [Member] | Call Options [Member]
Derivative assets:
Derivative Assets - Commodity swaps, collars, call and put options	(4,723)	(29,348)
Crude Oil [Member] | Put Options [Member]
Derivative assets:
Derivative Assets - Commodity swaps, collars, call and put options	1,071
NGLs [Member] | C3 Swap [Member]
Derivative assets:
Derivative Assets - Commodity swaps, collars, call and put options	2,333
Derivative liabilities:
Derivative Liabilities - Commodity swaps, collars, call and put options	(1,613)
NGLs [Member] | C5 Swap [Member]
Derivative assets:
Derivative Assets - Commodity swaps, collars, call and put options	79,492	15,328
Derivative liabilities:
Derivative Liabilities - Commodity swaps, collars, call and put options	$ (3,232)	$ (173)