Disclosure About Oil and Gas Producing Activities (Unaudited) (Details)	12 Months Ended
	Dec. 31, 2011 Bbl	Dec. 31, 2010 Bbl	Dec. 31, 2009 Bbl
Oil Reserves [Member]
Increase (Decrease) in Proved Developed and Undeveloped Reserves [Roll Forward]
Reserves, Beginning Balance	31,684,000	29,185,000	27,007,000
Extensions, discoveries and additions	4,592,000	7,369,000	5,902,000
Production	(1,408,000)	(1,334,000)	(1,320,000)
Revisions	(1,787,000)	(3,536,000)	(2,404,000)
Reserves, Ending Balance	33,081,000	31,684,000	29,185,000
Natural Gas Reserves [Member]
Increase (Decrease) in Proved Developed and Undeveloped Reserves [Roll Forward]
Reserves, Beginning Balance	4,200,155,000	3,736,601,000	3,355,788,000
Extensions, discoveries and additions	1,112,147,000	1,055,047,000	758,659,000
Production	(236,832,000)	(205,613,000)	(172,189,000)
Revisions	(296,916,000)	(385,880,000)	(205,657,000)
Reserves, Ending Balance	4,778,554,000	4,200,155,000	3,736,601,000