Derivative Financial Instruments (Summary of Interest Rate Derivatives and Offsetting Positions) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Derivative Assets
Derivative assets	$ 301,368	$ 103,644	$ 75,504
Derivative Liabilities
Gross Amounts Recognized	367,620	129,204	73,868
Interest rate derivatives
Derivative Assets
Derivative assets	259,986	100,569	68,317
Less: Amounts offset in the Statements of Condition	0	0	0
Net amount presented in the Statements of Condition	259,986	100,569	68,317
Offsetting Derivative Positions	(1,048)	(2,561)	(18,878)
Collateral Posted	0	0	0
Net Credit Exposure	258,938	98,008	49,439
Derivative Liabilities
Gross Amounts Recognized	329,590	126,805	69,292
Less: Amounts offset in the Statements of Condition	0	0	0
Net amount presented in the Statements of Condition	329,590	126,805	69,292
Offsetting Derivative Positions	(1,048)	(2,561)	(18,878)
Collateral Posted	(328,542)	(124,244)	(45,540)
Net Credit Exposure	$ 0	$ 0	$ 4,874