Derivative Instruments and Balance Sheet Offsetting - Balance Sheet Offsetting (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Offsetting derivative assets
Gross amounts recognized	$ 45,561	$ 18,681
Offsetting derivative liabilities
Gross amounts recognized	22,966	12,357
Interest rate swaps and customer-initiated derivatives
Offsetting derivative assets
Gross amounts recognized	21,376	15,228
Gross amounts offset in the statements of financial condition	0	0
Net amounts presented in the statements of financial position	21,376	15,228
Gross amounts not offset in the statements of financial position
Financial instruments	0	0
Collateral (received)/posted	(26,520)	0
Net Amount	(5,144)	15,228
Offsetting derivative liabilities
Gross amounts recognized	21,648	10,139
Gross amounts offset in the statements of financial condition	0	0
Net amounts presented in the statements of financial position	21,648	10,139
Gross amounts not offset in the statements of financial position
Financial instruments	0	0
Collateral (received)/posted	5,150	1,081
Net Amount	$ 16,498	$ 9,058