Derivative Financial Instruments (Summary of Interest Rate Derivatives and Offsetting Positions) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Derivative Assets
Derivative assets	$ 321,488	$ 103,644	$ 138,286
Derivative Liabilities
Gross Amounts Recognized	326,990	129,204	171,009
Interest rate derivatives
Derivative Assets
Derivative assets	253,238	100,569	134,386
Less: Amounts offset in the Statements of Condition	0	0	0
Net amount presented in the Statements of Condition	253,238	100,569	134,386
Offsetting Derivative Positions	(353)	(2,561)	(1,572)
Collateral Posted	0	0	0
Net Credit Exposure	252,885	98,008	132,814
Derivative Liabilities
Gross Amounts Recognized	318,853	126,805	168,897
Less: Amounts offset in the Statements of Condition	0	0	0
Net amount presented in the Statements of Condition	318,853	126,805	168,897
Offsetting Derivative Positions	(353)	(2,561)	(1,572)
Collateral Posted	(318,071)	(124,244)	(167,325)
Net Credit Exposure	$ 429	$ 0	$ 0