Derivative Instruments and Hedging Activities - Offsetting Assets and Liabilities in the Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Derivative assets
Gross amounts of recognized assets	$ 60,105	$ 2,239
Gross amounts offset in the statement of financial position	(2,440)	0
Net amounts of assets presented in the statement of financial position	57,665	2,239
Gross amounts of financial instruments not offset in the statement of financial position	0	0
Net amount	57,665	2,239
Derivative liabilities
Gross amounts of recognized liabilities	2,440	30,637
Gross amounts offset in the statement of financial position	(2,440)	0
Net amounts of liabilities presented in the statement of financial position	0	30,637
Gross amounts of financial instruments not offset in the statement of financial position	0	241
Net amount	$ 0	$ 30,878