Derivative Financial Instruments (Details 2) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Estimated volumes, fixed prices and fair values attributable to all of company oil and gas derivative contracts
Fair value, net	$ 43,171	$ 62,485
Remainder of 2012 [Member]
Estimated volumes, fixed prices and fair values attributable to all of company oil and gas derivative contracts
Fair value, net	13,259
Year Ending 2012 [Member]
Estimated volumes, fixed prices and fair values attributable to all of company oil and gas derivative contracts
Fair value, net		37,580
Year Ending 2013 [Member]
Estimated volumes, fixed prices and fair values attributable to all of company oil and gas derivative contracts
Fair value, net	29,226	24,905
Year Ending 2014 [Member]
Estimated volumes, fixed prices and fair values attributable to all of company oil and gas derivative contracts
Fair value, net	557
Year Ending 2015-2016 [Member]
Estimated volumes, fixed prices and fair values attributable to all of company oil and gas derivative contracts
Fair value, net	129
Natural Gas Swaps [Member]
Estimated volumes, fixed prices and fair values attributable to all of company oil and gas derivative contracts
Contract volumes (Mmbtu)	15,571,595	20,000,007
Weighted-average fixed price per Mmbtu	6.51	7.20
Fair value, net	47,882	72,319
Natural Gas Swaps [Member] | Remainder of 2012 [Member]
Estimated volumes, fixed prices and fair values attributable to all of company oil and gas derivative contracts
Contract volumes (Mmbtu)	5,524,592
Weighted-average fixed price per Mmbtu	5.71
Fair value, net	15,359
Natural Gas Swaps [Member] | Year Ending 2012 [Member]
Estimated volumes, fixed prices and fair values attributable to all of company oil and gas derivative contracts
Contract volumes (Mmbtu)		11,000,004
Weighted-average fixed price per Mmbtu		7.13
Fair value, net		42,803
Natural Gas Swaps [Member] | Year Ending 2013 [Member]
Estimated volumes, fixed prices and fair values attributable to all of company oil and gas derivative contracts
Contract volumes (Mmbtu)	9,000,003	9,000,003
Weighted-average fixed price per Mmbtu	7.28	7.28
Fair value, net	32,981	29,516
Natural Gas Swaps [Member] | Year Ending 2015-2016 [Member]
Estimated volumes, fixed prices and fair values attributable to all of company oil and gas derivative contracts
Contract volumes (Mmbtu)	1,047,000
Weighted-average fixed price per Mmbtu	4.00
Fair value, net	(458)
Natural Gas Basis Swaps [Member]
Estimated volumes, fixed prices and fair values attributable to all of company oil and gas derivative contracts
Contract volumes (Mmbtu)	13,524,593	18,000,003
Weighted-average fixed price per Mmbtu	(0.71)	(0.71)
Fair value, net	(6,976)	(9,378)
Natural Gas Basis Swaps [Member] | Remainder of 2012 [Member]
Estimated volumes, fixed prices and fair values attributable to all of company oil and gas derivative contracts
Contract volumes (Mmbtu)	4,524,590
Weighted-average fixed price per Mmbtu	(0.72)
Fair value, net	(2,356)
Natural Gas Basis Swaps [Member] | Year Ending 2012 [Member]
Estimated volumes, fixed prices and fair values attributable to all of company oil and gas derivative contracts
Contract volumes (Mmbtu)		9,000,000
Weighted-average fixed price per Mmbtu		(0.70)
Fair value, net		(4,767)
Natural Gas Basis Swaps [Member] | Year Ending 2013 [Member]
Estimated volumes, fixed prices and fair values attributable to all of company oil and gas derivative contracts
Contract volumes (Mmbtu)	9,000,003	9,000,003
Weighted-average fixed price per Mmbtu	(0.71)	(0.71)
Fair value, net	(4,620)	(4,611)
Crude Oil Swaps [Member]
Estimated volumes, fixed prices and fair values attributable to all of company oil and gas derivative contracts
Contract volumes (Mmbtu)	272,970	42,000
Weighted-average fixed price per Mmbtu	95.82	87.90
Fair value, net	2,265	(456)
Crude Oil Swaps [Member] | Remainder of 2012 [Member]
Estimated volumes, fixed prices and fair values attributable to all of company oil and gas derivative contracts
Contract volumes (Mmbtu)	33,342
Weighted-average fixed price per Mmbtu	93.86
Fair value, net	256
Crude Oil Swaps [Member] | Year Ending 2012 [Member]
Estimated volumes, fixed prices and fair values attributable to all of company oil and gas derivative contracts
Contract volumes (Mmbtu)		42,000
Weighted-average fixed price per Mmbtu		87.90
Fair value, net		(456)
Crude Oil Swaps [Member] | Year Ending 2013 [Member]
Estimated volumes, fixed prices and fair values attributable to all of company oil and gas derivative contracts
Contract volumes (Mmbtu)	65,892
Weighted-average fixed price per Mmbtu	101.70
Fair value, net	865
Crude Oil Swaps [Member] | Year Ending 2014 [Member]
Estimated volumes, fixed prices and fair values attributable to all of company oil and gas derivative contracts
Contract volumes (Mmbtu)	61,680
Weighted-average fixed price per Mmbtu	97.00
Fair value, net	557
Crude Oil Swaps [Member] | Year Ending 2015-2016 [Member]
Estimated volumes, fixed prices and fair values attributable to all of company oil and gas derivative contracts
Contract volumes (Mmbtu)	112,056
Weighted-average fixed price per Mmbtu	92.29
Fair value, net	$ 587