Oil And Natural Gas Properties (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Oil And Natural Gas Properties [Line Items]
Discount rate used to calculate ceiling, percentage			10.00%
Impairment of oil and gas properties	$ 115,874,000	$ 0	$ 115,874,000	$ 0
Impairment of oil and gas properties, net of taxes	72,100,000		72,100,000
Effects of cash flow hedges	$ 32,500,000		$ 32,500,000
Jul'12 - Dec'12 [Member]
Oil And Natural Gas Properties [Line Items]
Oil and gas production volume covered by hedges that affect ceiling determination, MMBoe	2.9		2.9
Jan'13 - Dec'13 [Member]
Oil And Natural Gas Properties [Line Items]
Oil and gas production volume covered by hedges that affect ceiling determination, MMBoe	4.5		4.5