Derivatives (Effects of Derivative Instruments on the Statements of Income) (Details) - Derivatives Designated as Hedging Instruments [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Derivative income reflected in income statement	$ 8,704	$ 1,479	$ 13,526	$ (716)
Other Noninterest Income [Member] | All Other Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative income reflected in income statement	4,108	3,600	7,979	4,409
Cash Flow Hedge [Member] | Interest Income [Member] | Variable Rate Loans [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative income reflected in income statement	4,597	(1,660)	5,461	(3,676)
Fair Value Hedging [Member] | Interest Income [Member] | Securities [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative income reflected in income statement	$ (1)		40
Fair Value Hedging [Member] | Interest Expense [Member] | Brokered Deposits [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative income reflected in income statement		$ (461)	$ 46	$ (1,449)