Derivative Instruments and Hedging Activities - Effect of Derivative Instruments on the Condensed Consolidated Statement of Operations (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Cash received (paid) on settlement of derivative instruments, gain (loss) on derivative instruments	$ (26,131)	$ (1,524)
Non-cash gain (loss) on derivative instruments, gain (loss) on derivative instruments	31,708	34,908
Gain (loss) on derivative instruments	$ 5,577	$ 33,384