Derivative Financial Instruments (Summary of Interest Rate Derivatives) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Derivative Assets
Gross Amounts Recognized	$ 73,172	$ 52,069
Derivative Liabilities
Gross Amounts Recognized	68,088	35,671
Interest rate derivatives
Derivative Assets
Gross Amounts Recognized	68,425	48,985
Less: Amounts offset in the Statements of Condition	0	0
Net amount presented in the Statements of Condition	68,425	48,985
Offsetting Derivative Positions	(28,124)	(14,878)
Collateral Posted	(23,810)	(18,060)
Net Credit Exposure	16,491	16,047
Derivative Liabilities
Gross Amounts Recognized	62,571	33,716
Less: Amounts offset in the Statements of Condition	0	0
Net amount presented in the Statements of Condition	62,571	33,716
Offsetting Derivative Positions	(28,124)	(14,878)
Collateral Posted	(2,640)	(2,220)
Net Credit Exposure	$ 31,807	$ 16,618