Supplemental Financial Information Exploration and Production (Details 4) (Details)	12 Months Ended
	Dec. 31, 2011 Mcfe	Dec. 31, 2010 Mcfe	Dec. 31, 2009 Mcfe
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved developed and undeveloped reserves, starting balance	645,596,000	653,724,000	810,371,000
Proved Developed and Undeveloped Reserves, Production	(66,596,000)	(69,963,000)	(75,299,000)
Proved Developed and Undeveloped Reserves, Extensions, Discoveries, and Additions	65,049,000	56,523,000	42,297,000
Proved Developed and Undeveloped Reserves, Improved Recovery	0	0	0
Proved Developed and Undeveloped Reserves, Purchases of Minerals in Place	1,486,000	60,991,000	0
Proved Developed and Undeveloped Reserves, Sales of Minerals in Place	0	(202,000)	(1,510,000)
Proved Developed and Undeveloped Reserves, Revisions of Previous Estimates	(59,627,000)	(55,477,000)	(122,135,000)
Proved developed and undeveloped reserves, ending balance	585,908,000	645,596,000	653,724,000
Reduction in proved undeveloped reserves	53,600,000
Natural Gas Reserves [Member]
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved developed and undeveloped reserves, starting balance	448,397	448,425	604,282
Proved Developed and Undeveloped Reserves, Production	(45,598)	(50,391)	(56,632)
Proved Developed and Undeveloped Reserves, Extensions, Discoveries, and Additions	28,221	36,191	26,882
Proved Developed and Undeveloped Reserves, Improved Recovery	0	0	0
Proved Developed and Undeveloped Reserves, Purchases of Minerals in Place	54	55,119	0
Proved Developed and Undeveloped Reserves, Sales of Minerals in Place	0	(92)	(22)
Proved Developed and Undeveloped Reserves, Revisions of Previous Estimates	(51,247)	(40,855)	(126,085)
Proved developed and undeveloped reserves, ending balance	379,827	448,397	448,425
Oil Reserves [Member]
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved developed and undeveloped reserves, starting balance	32,867	34,216	34,348
Proved Developed and Undeveloped Reserves, Production	(3,500)	(3,262)	(3,111)
Proved Developed and Undeveloped Reserves, Extensions, Discoveries, and Additions	6,138	3,389	2,569
Proved Developed and Undeveloped Reserves, Improved Recovery	0	0	0
Proved Developed and Undeveloped Reserves, Purchases of Minerals in Place	239	979	0
Proved Developed and Undeveloped Reserves, Sales of Minerals in Place	0	(18)	(248)
Proved Developed and Undeveloped Reserves, Revisions of Previous Estimates	(1,397)	(2,437)	658
Proved developed and undeveloped reserves, ending balance	34,347	32,867	34,216