Supplemental Gas Data Oil and Gas Reserve Quantities (Details) (USD $)	12 Months Ended				12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008	Dec. 31, 2011 proved undeveloped [Member]	Jan. 02, 2011 proved undeveloped [Member]	Dec. 31, 2011 Natural Gas Reserves [Member]	Dec. 31, 2010 Natural Gas Reserves [Member]	Dec. 31, 2009 Natural Gas Reserves [Member]	Dec. 31, 2008 Natural Gas Reserves [Member]	Dec. 31, 2011 Oil Reserves [Member]	Dec. 31, 2010 Oil Reserves [Member]	Dec. 31, 2009 Oil Reserves [Member]	Dec. 31, 2008 Oil Reserves [Member]
Reserve Quantities [Line Items]
Payments to Acquire Property, Plant, and Equipment	$ 1,382,371,000	$ 1,154,024,000	$ 920,080,000		$ 134,064
Proved Developed Reserves (Volume)	2,135,805,000	1,931,272,000	1,040,257,000	783,290,000			2,126,330,000	1,924,036,000	1,039,052,000	783,010,000	9,475,000	7,236,000	1,205,000	280,000
Proved undeveloped reserves (Volume)	1,344,222,000	1,800,325,000	871,134,000	638,756,000	1,344,222,000	1,800,325,000	1,344,222,000	1,800,325,000	871,134,000	638,756,000	0	0	0	0
undeveloped reserves transferred to developed					(200,849,000)
Beginning reserves	3,480,027,000	3,731,597,000	1,911,391,000	1,422,046,000
Revisions(a)	(83,813,000)	379,977,000	177,004,000		(362,770,000)
Extensions and discoveries(b)	517,178,000	621,270,000	406,756,000		386,097,000
Proved Developed and Undeveloped Reserves, Production	153,504,000	127,875,000	94,415,000
Purchases of reserves in-place	0	946,834,000	0
Sale of reserves in-place	(531,431,000)	0	0		(278,581,000)