Derivative Instruments and Hedging Activities - Offsetting Assets and Liabilities in the Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Derivative assets
Gross amounts of recognized assets	$ 0	$ 137,603
Gross amounts offset in the statement of financial position	0	0
Net amounts of assets presented in the statement of financial position	0	137,603
Gross amounts of financial instruments not offset in the statement of financial position	0	(2,338)
Net amount	$ 0	$ 139,941