Fair Value Measurements and Disclosures (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013
Fair Value | Significant Other Observable Inputs (Level 2)
Assets and Liabilities at Fair Value
Commodity-based derivative - assets	$ 20,817,000	$ 3,852,000
Basis protection derivative - assets	0	74,000
Total assets	20,817,000	3,926,000
Commodity-based derivative - liabilities	4,079,000	16,539,000
Basis protection derivative - liabilities	81,000	5,000
Total liabilities	4,160,000	16,544,000
Net asset (fair value)	16,657,000	(12,618,000)
Fair Value | Significant Unobservable Inputs (Level 3)
Assets and Liabilities at Fair Value
Commodity-based derivative - assets	6,369,000	2,098,000
Basis protection derivative - assets	0	0
Total assets	6,369,000	2,098,000
Commodity-based derivative - liabilities	437,000	987,000
Basis protection derivative - liabilities	0	0
Total liabilities	437,000	987,000
Net asset (fair value)	5,932,000	1,111,000
Fair Value | Total
Assets and Liabilities at Fair Value
Commodity-based derivative - assets	27,186,000	5,950,000
Basis protection derivative - assets	0	74,000
Total assets	27,186,000	6,024,000
Commodity-based derivative - liabilities	4,516,000	17,526,000
Basis protection derivative - liabilities	81,000	5,000
Total liabilities	4,597,000	17,531,000
Net asset (fair value)	22,589,000	(11,507,000)
3.25% Convertible Senior Notes due 2016
Assets and Liabilities at Fair Value
Debt Instrument, Interest Rate, Stated Percentage	3.25%
3.25% convertible senior notes fair value	158,500,000
3.25% convertible senior notes fair value as a percentage of par	137.80%
7.75% Senior Notes due 2022
Assets and Liabilities at Fair Value
Debt Instrument, Interest Rate, Stated Percentage	7.75%
7.75% senior notes fair value	$ 536,300,000
7.75% senior notes fair value as percentage of par	107.30%