Derivative Financial Instruments (Summary of Interest Rate Derivatives and Offsetting Positions) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019
Derivative Assets
Derivative assets	$ 327,624	$ 103,644	$ 108,784
Derivative Liabilities
Gross Amounts Recognized	355,265	129,204	136,312
Interest rate derivatives
Derivative Assets
Derivative assets	268,709	100,569	104,562
Less: Amounts offset in the Statements of Condition	0	0	0
Net amount presented in the Statements of Condition	268,709	100,569	104,562
Offsetting Derivative Positions	(697)	(2,561)	(3,934)
Collateral Posted	0	0	0
Net Credit Exposure	268,012	98,008	100,628
Derivative Liabilities
Gross Amounts Recognized	343,519	126,805	131,035
Less: Amounts offset in the Statements of Condition	0	0	0
Net amount presented in the Statements of Condition	343,519	126,805	131,035
Offsetting Derivative Positions	(697)	(2,561)	(3,934)
Collateral Posted	(342,276)	(124,244)	(127,101)
Net Credit Exposure	$ 546	$ 0	$ 0