Decommissioning and Other Asset Retirement Obligations (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Decommissioning and Other Asset Retirement Obligations Detail [Table]
Beginning balance for the period, as reported	$ 139,835,000	$ 272,815,000
Activity in the period:
Accretion of liability	1,536,000	4,325,000
Retirement obligations incurred	0	0
Revisions in estimated cash flows	40,986,000	79,360,000
Settlement of retirement obligations	(87,436,000)	(216,665,000)
Ending balance at December 31	94,921,000	139,835,000	272,815,000
Change in estimated cash flows to decommission oil and gas properties	41,000,000
Direct charges to operating expense for increased estimated cash flows	40,767,000	78,382,000	53,997,000
Aggregate amount of asset retirement obligations assumed by buyers of oil and gas properties		122,000,000
Estimated future hurricane repair expenses	$ 13,900,000	$ 0