Property And Equipment (Summary of Net Property and Equipment) (Details) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Property, Plant and Equipment [Line Items]
Less accumulated depletion, depreciation, amortization and impairment	$ (3,180,241,000)	$ (2,627,493,000)
Net property and equipment	8,077,110,000	8,011,625,000
Oil and natural gas properties [Abstract]
Proved properties	6,963,211,000	7,026,579,000
Unevaluated properties	809,154,000	1,157,106,000
Total	7,772,365,000	8,183,685,000
Accumulated depletion and depreciation of oil and natural gas properties	(2,827,256,000)	(2,407,520,000)
Net oil and natural gas properties	4,945,109,000	5,776,165,000
CO2 Properties [Abstract]
CO2 properties	1,032,653,000	596,003,000
Pipelines and plants [Abstract]
CO2 pipelines	1,632,255,000	1,432,646,000
Plants under construction	402,871,000	269,110,000
Total	2,035,126,000	1,701,756,000
Other property and equipment [Abstract]
Other property and equipment	417,207,000	157,674,000
CO2 pipelines not placed in service	346,500,000
Co2 Properties [Member]
Property, Plant and Equipment [Line Items]
Less accumulated depletion, depreciation, amortization and impairment	(119,784,000)	(91,666,000)
Net property and equipment	912,869,000	504,337,000
Pipelines And Plants [Member]
Property, Plant and Equipment [Line Items]
Less accumulated depletion, depreciation, amortization and impairment	(99,185,000)	(65,392,000)
Net property and equipment	1,935,941,000	1,636,364,000
Other property and equipment [Member]
Property, Plant and Equipment [Line Items]
Less accumulated depletion, depreciation, amortization and impairment	(134,016,000)	(62,915,000)
Net property and equipment	$ 283,191,000	$ 94,759,000