Fair Value Measurement (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis
Asset impairment charges related to write down of drilling rigs			$ 4,200,000
Impairment of oil and natural gas properties	625,564,000	0	1,017,000
Assets and liabilities measured on a recurring basis | Estimated Fair Value | Commodity contract
Fair Value, Assets and Liabilities Measured on Recurring Basis
Commodity derivative asset (liability), net	22,700,000	113,600,000
Assets and liabilities measured on a recurring basis | Level 1 | Commodity contract
Fair Value, Assets and Liabilities Measured on Recurring Basis
Commodity derivative asset (liability), net	0	0
Assets and liabilities measured on a recurring basis | Level 2 | Commodity contract
Fair Value, Assets and Liabilities Measured on Recurring Basis
Commodity derivative asset (liability), net	22,700,000	11,800,000
Assets and liabilities measured on a recurring basis | Level 3 | Commodity contract
Fair Value, Assets and Liabilities Measured on Recurring Basis
Commodity derivative asset (liability), net	0	101,800,000
Assets measured on nonrecurring basis
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis
Total impairment recognized	629,300,000
Oil and Gas Properties | Assets measured on nonrecurring basis | Level 1
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis
Property, Plant and Equipment, Fair Value Disclosure	0
Oil and Gas Properties | Assets measured on nonrecurring basis | Level 2
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis
Property, Plant and Equipment, Fair Value Disclosure	0
Oil and Gas Properties | Assets measured on nonrecurring basis | Level 3
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis
Property, Plant and Equipment, Fair Value Disclosure	114,300,000
Other Long-Lived Assets | Assets measured on nonrecurring basis
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis
Asset impairment charges related to write down of drilling rigs	4,300,000	0	4,200,000
Other Long-Lived Assets | Assets measured on nonrecurring basis | Level 1
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis
Property, Plant and Equipment, Fair Value Disclosure	0		0
Other Long-Lived Assets | Assets measured on nonrecurring basis | Level 2
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis
Property, Plant and Equipment, Fair Value Disclosure	0		0
Other Long-Lived Assets | Assets measured on nonrecurring basis | Level 3
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis
Property, Plant and Equipment, Fair Value Disclosure	1,400,000		3,300,000
East Texas | Oil and Gas Properties | Assets measured on nonrecurring basis
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis
Impairment of oil and natural gas properties	$ 625,000,000