Derivative Instruments and Hedging Activities - Effect of Derivative Instruments on the Condensed Consolidated Statement of Operations (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Cash received (paid) on settlement of derivative instruments, gain (loss) on derivative instruments	$ 3,906	$ (8,101)	$ 3,587	$ 3,204
Non-cash gain (loss) on derivative instruments, gain (loss) on derivative instruments	(4,742)	15,005	42,766	(4,490)
Gain (loss) on derivative instruments	$ (836)	$ 6,904	$ 46,353	$ (1,286)