Fair Value Measurements and Derivative Instruments - Offsetting of Derivative Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Offsetting of Financial Assets under Master Netting Agreements [Abstract]
Gross Amount of Derivative Assets Presented in the Consolidated Balance Sheet	$ 68,693	$ 19,397
Gross Amount of Eligible Offsetting Recognized Derivative Liabilities	(45,156)	(19,397)
Net Amount of Derivative Assets	23,537	0
Offsetting of Financial Liabilities under Master Netting Agreements [Abstract]
Gross Amount of Derivative Liabilities Presented in the Consolidated Balance Sheet	(266,257)	(373,497)
Gross Amount of Eligible Offsetting Recognized Derivative Assets	45,156	19,397
Cash Collateral Pledged	0	7,213
Net Amount of Derivative Liabilities	$ (221,101)	$ (346,887)