Disclosure About Oil and Gas Producing Activities (Unaudited) (Details)	12 Months Ended
	Dec. 31, 2012 Bbl	Dec. 31, 2011 Bbl	Dec. 31, 2010 Bbl
Oil Reserves [Member]
Increase (Decrease) in Proved Developed and Undeveloped Reserves [Roll Forward]
Reserves, Beginning Balance	33,081,000	31,684,000	29,185,000
Extensions, discoveries and additions	5,435,000	7,425,000	8,496,000
Production	(1,282,000)	(1,408,000)	(1,334,000)
Revisions	(19,097,000)	(4,620,000)	(4,663,000)
Reserves, Ending Balance	18,137,000	33,081,000	31,684,000
Natural Gas Reserves [Member]
Increase (Decrease) in Proved Developed and Undeveloped Reserves [Roll Forward]
Reserves, Beginning Balance	4,778,554,000	4,200,155,000	3,736,601,000
Extensions, discoveries and additions	819,896,000	1,452,122,000	1,195,829,000
Production	(249,310,000)	(236,832,000)	(205,613,000)
Revisions	(2,382,695,000)	(636,891,000)	(526,662,000)
Reserves, Ending Balance	2,966,445,000	4,778,554,000	4,200,155,000