Derivative Instruments and Hedging Activities - Effect of Derivative on Income Statement (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Unrealized gain (loss) on derivative instruments	$ (38,950)	$ 56,686	$ 219,319
Gain (loss) in derivative instruments not designated as hedges	(38,950)	56,686	145,891
Gain (loss) on derivative, net	(38,950)	56,686	75,116
Derivatives Designated as Hedges
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Realized gain (loss) on derivative instruments	0	0	(70,775)
Derivatives Not Designated as Hedges
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Unrealized gain (loss) on derivative instruments	(37,268)	(137,603)	137,603
Natural gas | Derivatives Designated as Hedges
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Realized gain (loss) on derivative instruments	0	0	(70,557)
Natural gas | Derivatives Not Designated as Hedges
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Realized gain (loss) on derivative instruments	0	0	(73,020)
Crude oil and condensate | Derivatives Designated as Hedges
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Realized gain (loss) on derivative instruments	0	0	(218)
Crude oil and condensate | Derivatives Not Designated as Hedges
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Realized gain (loss) on derivative instruments	0	0	(408)
Gain (loss) on derivative instruments | Derivatives Not Designated as Hedges
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Realized gain (loss) on derivative instruments	$ (1,682)	$ 194,289	$ 81,716