Derivative Instruments and Balance Sheet Offsetting (Balance Sheet Offsetting) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Offsetting derivative assets
Gross amounts recognized	$ 18,681	$ 8,215
Offsetting derivative liabilities
Gross amounts recognized	12,357	6,359
Interest rate swaps and customer-initiated derivatives
Offsetting derivative assets
Gross amounts recognized	15,228	4,405
Gross amounts offset in the statements of financial condition	0	0
Net amounts presented in the statements of financial position	15,228	4,405
Gross amounts of assets not offset in the statement of financial position
Financial instruments	0	0
Collateral (received)/posted	0	0
Net Amount	15,228	4,405
Offsetting derivative liabilities
Gross amounts recognized	10,139	4,141
Gross amounts offset in the statements of financial condition	0	0
Net amounts presented in the statements of financial position	10,139	4,141
Gross amounts of liabilities not offset in the statement of financial position
Financial instruments	0	0
Collateral (received)/posted	1,081	2,550
Net Amount	$ 9,058	$ 1,591