Fair Value Measurements and Derivative Instruments - Offsetting of Derivative Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Offsetting of Financial Assets under Master Netting Agreements [Abstract]
Gross Amount of Derivative Assets Presented in the Consolidated Balance Sheet	$ 36,697	$ 134,574
Gross Amount of Eligible Offsetting Recognized Derivative Liabilities	(34,517)	(129,815)
Net Amount of Derivative Assets	2,180	4,759
Offsetting of Financial Liabilities under Master Netting Agreements [Abstract]
Gross Amount of Derivative Liabilities Presented in the Consolidated Balance Sheet	(507,202)	(1,044,292)
Gross Amount of Eligible Offsetting Recognized Derivative Assets	34,517	129,815
Net Amount of Derivative Liabilities	$ (472,685)	$ (914,477)