Derivative Instruments and Balance Sheet Offsetting - Balance Sheet Offsetting (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Offsetting derivative assets
Gross amounts recognized	$ 28,998	$ 18,681
Offsetting derivative liabilities
Gross amounts recognized	13,960	12,357
Interest rate swaps and customer-initiated derivatives
Offsetting derivative assets
Gross amounts recognized	25,698	15,228
Gross amounts offset in the statements of financial condition	0	0
Net amounts presented in the statements of financial position	25,698	15,228
Gross amounts not offset in the statements of financial position
Financial instruments	0	0
Collateral (received)/posted	(17,243)	0
Net Amount	8,455	15,228
Offsetting derivative liabilities
Gross amounts recognized	12,009	10,139
Gross amounts offset in the statements of financial condition	0	0
Net amounts presented in the statements of financial position	12,009	10,139
Gross amounts not offset in the statements of financial position
Financial instruments	0	0
Collateral (received)/posted	230	1,081
Net Amount	$ 11,779	$ 9,058