Oil And Gas Properties (Narrative) (Details) (USD $)	1 Months Ended	3 Months Ended						6 Months Ended	9 Months Ended		12 Months Ended
	Feb. 28, 2010	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Jun. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2007	Dec. 31, 2010
Oil and gas property impairments			$ 2,357,000	$ 22,700,000	$ 897,000	$ 159,900,000	$ 7,000,000		$ 25,078,000	$ 171,871,000
Oil and gas properties				6				15
Oil and gas properties subject to impairment charges							3
Asset retirement obligation			233,245,000						233,245,000			234,936,000
Capitalized exploration cost			4,600,000						4,600,000
Working interest in oil and gas field											100.00%
Cash acquired from acquisition	10,200,000
Acquired working interest	50.00%
Approximate gain on acquisition	6,000,000
Working interest before acquisition							50.00%
Hurricane-related repair costs					900,000					4,600,000
Insurance reimbursements									5,000,000
General insurance expense		2,000,000	8,400,000
Hurricane Catastrophic Bond [Member]
Prepaid insurance				10,600,000
Non-Domestic Oil And Gas Property [Member]
Oil and gas property impairments				4,100,000			4,100,000
Asset retirement obligation			11,600,000						11,600,000
Accrued reclamation costs, current			$ 4,800,000						$ 4,800,000