Derivative Commodity Instruments - Not Designated as Hedging Instruments on the Income Statement (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain on fair value of derivatives	$ 38,101	$ (65,872)	$ 102,647	$ (60,417)
Gain (loss) on derivative instruments, net
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain on fair value of derivatives	$ 38,101	$ (65,872)	$ 102,647	$ (60,417)