Derivative Commodity Instruments - Not Designated as Hedging Instruments on the Income Statement (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Gain (loss) on derivative instruments, net
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain (loss) recognized in income on derivatives	$ 107,173	$ 141,743	$ 90,245	$ (6,283)