Supplemental Oil and Natural Gas Disclosures (Unaudited) (Details 1) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Results of operations from oil and natural gas producing activities excluding corporate overhead and interest costs
Oil, natural gas and related product sales	$ 2,269,151,000	$ 1,793,292,000	$ 866,709,000
Lease operating expenses	507,397,000	470,364,000	314,689,000
Marketing expenses	26,047,000	31,036,000	16,890,000
Taxes other than income	138,419,000	114,569,000	37,037,000
Commodity derivative expense (income)	(52,497,000)	(21,414,000)	236,226,000
Net operating income	1,256,250,000	777,749,000	25,792,000
Income tax provision	477,375,000	295,545,000	9,927,000
Results of operations from oil and natural gas producing activities	778,875,000	482,204,000	15,865,000
Depletion, depreciation and amortization per BOE	16.42	15.82	13.39
Oil and Gas [Member]
Results of operations from oil and natural gas producing activities excluding corporate overhead and interest costs
Depletion, depreciation and amortization	369,075,000	391,782,000	206,999,000
Co2 Property And Pipelines [Member]
Results of operations from oil and natural gas producing activities excluding corporate overhead and interest costs
Depletion, depreciation and amortization	$ 24,460,000	$ 29,206,000	$ 29,076,000