Derivatives (Effects of Derivative Instruments on the Statements of Income) (Details) - Derivatives Designated as Hedging Instruments [Member] - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Derivative income reflected in income statement	$ 7,520	$ 3,140	$ 21,046	$ 2,424
Other Noninterest Income [Member] | All Other Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative income reflected in income statement	1,739	4,324	9,718	8,733
Cash Flow Hedge [Member] | Interest Income [Member] | Variable Rate Loans [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative income reflected in income statement	5,788	(956)	11,249	(4,632)
Fair Value Hedging [Member] | Interest Income [Member] | Securities [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative income reflected in income statement	$ (7)	15	33	15
Fair Value Hedging [Member] | Interest Expense [Member] | Brokered Deposits [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative income reflected in income statement		$ (243)	$ 46	$ (1,692)