Derivative Instruments and Hedging Activities - Offsetting of Derivative Assets and Liabilities in the Condensed Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Derivative assets
Gross amounts of recognized assets	$ 4,474	$ 2,239
Gross amounts offset in the statement of financial position	(1,062)	0
Net amounts of assets presented in the statement of financial position	3,412	2,239
Gross amounts of financial instruments not offset in the statement of financial position	0	0
Net amount	3,412	2,239
Derivative liabilities
Gross amounts of recognized liabilities	10,651	30,637
Gross amounts offset in the statement of financial position	(1,062)	0
Net amounts of liabilities presented in the statement of financial position	9,589	30,637
Gross amounts of financial instruments not offset in the statement of financial position	0	241
Net amount	$ 9,589	$ 30,878