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, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Derivative instruments and hedging activities
Gain (loss) on derivative instruments	$ 6,904	$ 17,364	$ (1,286)	$ 44,668
Derivatives Not Designated as Hedges | Gain (loss) on derivative instruments
Derivative instruments and hedging activities
Gain (loss) on derivative instruments	(8,101)	45,097	3,204	133,827
Non-cash gain (loss) on derivative instruments	$ 15,005	$ (27,733)	$ (4,490)	$ (89,159)