Fair Value Measurements and Disclosures (Details) (USD $)	Jun. 30, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
3.25% Convertible Senior Notes fair value	$ 215,700,000
12% Senior Notes fair value	108,200,000
3.25% Convertible Senior Notes Fair Value	94.10%
12% Senior Notes fair value	106.30%
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity Based Derivative Assets	78,442,000	76,104,000
Basis Protection Derivative Assets	25,000	5,000
Assets, Fair Value Disclosure	78,467,000	76,109,000
Commodity Based Derivative Liabilities	5,153,000	9,888,000
Basis Protection Derivative Liabilities	26,507,000	35,424,000
Liabilities, Fair Value Disclosure	31,660,000	45,312,000
Net Asset Fair Value	46,807,000	30,797,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity Based Derivative Assets	28,649,000	25,837,000
Basis Protection Derivative Assets	21,000	38,000
Assets, Fair Value Disclosure	28,670,000	25,875,000
Commodity Based Derivative Liabilities	70,000	3,768,000
Basis Protection Derivative Liabilities	0	0
Liabilities, Fair Value Disclosure	70,000	3,768,000
Net Asset Fair Value	28,600,000	22,107,000
Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity Based Derivative Assets	107,091,000	101,941,000
Basis Protection Derivative Assets	46,000	43,000
Assets, Fair Value Disclosure	107,137,000	101,984,000
Commodity Based Derivative Liabilities	5,223,000	13,656,000
Basis Protection Derivative Liabilities	26,507,000	35,424,000
Liabilities, Fair Value Disclosure	31,730,000	49,080,000
Net Asset Fair Value	$ 75,407,000	$ 52,904,000
3.25% Convertible Senior Notes due 2016 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.25%
12% Senior Notes due 2018 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	(12.00%)