Supplemental CO2 and Helium Disclosures (Unaudited) (Details)	Dec. 31, 2011 Bcf	Dec. 31, 2010 Bcf	Dec. 31, 2009 Bcf
Reserve Quantities [Line Items]
CO2 VPP	84.7	100.2	127.1
Gulf Coast Region [Member]
Reserve Quantities [Line Items]
CO2 Reserves	6,685,412	7,085,131	6,302,836
Net Revenue Interest In Co2 Reserves	5.3	5.6	5.0
Rocky Mountain Region [Member]
Reserve Quantities [Line Items]
CO2 Reserves	2,195,534	2,189,756	0
Helium Reserves	12,004	7,159	0
Net Revenue Interest In Co2 Reserves	1.6	0.9	0.0