Fair Value Measurements and Disclosures (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Fair Value | Significant Other Observable Inputs (Level 2)
Assets and Liabilities at Fair Value
Commodity-based derivative - assets	$ 49,021	$ 174,657
Basis protection derivative - assets	424	101
Total assets	49,445	174,758
Commodity-based derivative - liabilities	30,917	738
Basis protection derivative - liabilities	881	1,552
Total liabilities	31,798	2,290
Net asset (fair value)	17,647	172,468
Fair Value | Significant Unobservable Inputs (Level 3)
Assets and Liabilities at Fair Value
Commodity-based derivative - assets	24,582	91,288
Basis protection derivative - assets	0	0
Total assets	24,582	91,288
Commodity-based derivative - liabilities	8,650	0
Basis protection derivative - liabilities	0	0
Total liabilities	8,650	0
Net asset (fair value)	15,932	91,288
Fair Value | Total
Assets and Liabilities at Fair Value
Commodity-based derivative - assets	73,603	265,945
Basis protection derivative - assets	424	101
Total assets	74,027	266,046
Commodity-based derivative - liabilities	39,567	738
Basis protection derivative - liabilities	881	1,552
Total liabilities	40,448	2,290
Net asset (fair value)	$ 33,579	$ 263,756
1.125% Convertible Senior Notes due 2021 [Member]
Assets and Liabilities at Fair Value
Debt Instrument, Interest Rate, Stated Percentage	1.13%
7.75% senior notes fair value	$ 214,800
7.75% senior notes fair value as percentage of par	107.40%
6.125% Senior Notes due 2024 [Member]
Assets and Liabilities at Fair Value
Debt Instrument, Interest Rate, Stated Percentage	6.125%
7.75% senior notes fair value	$ 415,600
7.75% senior notes fair value as percentage of par	103.90%
7.75% Senior Notes due 2022 [Member]
Assets and Liabilities at Fair Value
Debt Instrument, Interest Rate, Stated Percentage	7.75%
7.75% senior notes fair value	$ 530,300
7.75% senior notes fair value as percentage of par	106.10%