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, 2016	Mar. 31, 2015
Derivative instruments and hedging activities
Gain (loss) on derivative instruments	$ 18,994	$ 34,123
Unrealized gain (loss) on derivative instruments	18,994	34,123
Gain (loss) on derivative instruments	18,994	34,123
Derivatives Not Designated as Hedges | Gain (loss) on derivative instruments
Derivative instruments and hedging activities
Gain (loss) on derivative instruments	0	37,685
Unrealized gain (loss) on derivative instruments	$ 18,994	$ (3,562)