Derivative Commodity Instruments - Gain (Loss) on Derivative Instruments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Loss on derivative instruments, net	$ (50,964)	$ (84,846)	$ (16,928)	$ (138,237)
Commodity contracts
Derivative Instruments, Gain (Loss) [Line Items]
Open non-cash mark-to-market losses on derivative instruments	(116,867)	(59,621)	(176,518)	(93,302)
Closed gains (losses) on derivative instruments	65,903	(25,225)	159,590	(44,935)
Loss on derivative instruments, net	$ (50,964)	$ (84,846)	$ (16,928)	$ (138,237)