Derivative Commodity Instruments - Gain (Loss) on Derivative Instruments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Gain on derivative instruments, net	$ 107,173	$ 147,735	$ 90,245	$ 9,498
Commodity contracts
Derivative Instruments, Gain (Loss) [Line Items]
Open non-cash mark-to-market gains (losses) on derivative instruments	(1,164)	147,287	(177,682)	53,985
Closed gains (losses) on derivative instruments	108,337	448	267,927	(44,487)
Gain on derivative instruments, net	$ 107,173	$ 147,735	$ 90,245	$ 9,498