Decommissioning and Other Asset Retirement Obligations (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Decommissioning and Other Asset Retirement Obligations Detail [Table]
Beginning balance for the period, as reported	$ 272,815,000	$ 224,110,000
Activity in the period:
Accretion of liability	4,325,000	5,539,000
Retirement obligations incurred	0	22,000
Revisions in estimated cash flows	79,360,000	131,889,000
Settlement of retirement obligations	(216,665,000)	(88,745,000)
Ending balance at December 31	139,835,000	272,815,000	224,110,000
Change in estimated cash flows to decommission oil and gas properties	80,200,000
Direct charges to operating expense for increased estimated cash flows	78,382,000	53,997,000	23,771,000
Aggregate amount of asset retirement obligations assumed by buyers of oil and gas properties	122,000,000		6,300,000
Estimated future hurricane repair expenses	$ 27,500,000