Derivative Instruments and Hedging Activities - Offsetting of Derivative Assets and Liabilities in the Condensed Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Derivative assets
Gross amounts of recognized assets	$ 6,605	$ 2,991
Gross amounts offset in the statement of financial position	(306)	0
Net amounts of assets presented in the statement of financial position	6,299	2,991
Gross amounts of financial instruments not offset in the statement of financial position	18	0
Net amount	6,317	2,991
Derivative liabilities
Gross amounts of recognized liabilities	1,106	40,259
Gross amounts offset in the statement of financial position	(306)	0
Net amounts of liabilities presented in the statement of financial position	800	40,259
Gross amounts of financial instruments not offset in the statement of financial position	0	757
Net amount	$ 800	$ 41,016