Derivatives (Effects of Derivative Instruments on the Statements of Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Derivative income reflected in income statement	$ 16,466	$ 8,704	$ 27,720	$ 13,526
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	3,750	4,108	8,785	7,979
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	6,855	4,597	12,991	5,461
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	(110)	$ (1)	(27)	40
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		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	$ 3,472		$ 3,472