Derivatives (Effects of Derivative Instruments on the Statements of Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Derivative income reflected in income statement	$ 8,692	$ 7,520	$ 36,412	$ 21,046
Derivatives Designated as Hedging Instruments [Member] | Other Noninterest Income [Member] | Customer and All Other Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative income reflected in income statement	2,970	1,739	11,755	9,718
Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedge [Member] | Interest Income [Member] | Interest Rate Swaps - Variable Rate Loans [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative income reflected in income statement	6,950	5,788	19,941	11,249
Derivatives Designated as Hedging Instruments [Member] | Fair Value Hedging [Member] | Interest Income [Member] | Interest Rate Swaps - Securities [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative income reflected in income statement	21	$ (7)	(6)	33
Derivatives Designated as Hedging Instruments [Member] | Fair Value Hedging [Member] | Securities Transactions Net [Member] | Securities Termination [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative income reflected in income statement			2,499
Derivatives Designated as Hedging Instruments [Member] | Fair Value Hedging [Member] | Interest Expense [Member] | Brokered Deposits [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative income reflected in income statement				$ 46
Derivatives Not Designated as Hedging Instruments [Member] | Secondary Mortgage Market Operations [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative income reflected in income statement	$ (1,249)		$ 2,223