Derivative Instruments and Hedging Activities - Offsetting of Derivative Assets and Liabilities in the Condensed Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Derivative assets
Gross amounts of recognized assets	$ 11,950	$ 2,239
Gross amounts offset in the statement of financial position	(637)	0
Net amounts of assets presented in the statement of financial position	11,313	2,239
Gross amounts of financial instruments not offset in the statement of financial position	4,728	0
Net amount	16,041	2,239
Derivative liabilities
Gross amounts of recognized liabilities	8,639	30,637
Gross amounts offset in the statement of financial position	(637)	0
Net amounts of liabilities presented in the statement of financial position	8,002	30,637
Gross amounts of financial instruments not offset in the statement of financial position	5,534	241
Net amount	$ 13,536	$ 30,878