Derivatives - Gains and Losses on Derivative Instruments Included in Statement of Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Change in fair value of open non-hedge derivative instruments	$ (26,522)	$ (112,918)	$ 117,109
Gain on settlement of non-hedge derivative instruments	1,177	144,869	10,430
Gain (loss) on derivative instruments	$ (25,345)	$ 31,951	$ 127,539