Derivatives (Narrative) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2025 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2025 USD ($) SwapAgreements	Sep. 30, 2024 USD ($) SwapAgreements	Dec. 31, 2024 USD ($)
Derivative [Line Items]
Notional amount of derivatives	$ 7,745,924,000		$ 7,745,924,000		$ 7,392,532,000
Payments (made) received to terminate hedge instruments			2,270,000	$ (13,730,000)
Fair value hedges resulting net earnings	(2,751,000)	$ (8,881,000)	(8,788,000)	(31,440,000)
Fair value liability	1,900,000		1,900,000		2,100,000
Credit risk-related contingent features, net liability position	17,500,000		17,500,000		39,100,000
Credit risk-related contingent features, posted collateral	17,800,000		17,800,000		38,000,000
Fair Value Hedging [Member]
Derivative [Line Items]
Fair value hedges resulting net earnings			203,500,000
Derivatives Designated as Hedging Instruments [Member]
Derivative [Line Items]
Notional amount of derivatives	2,122,500,000		$ 2,122,500,000		1,827,500,000
Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedge [Member]
Derivative [Line Items]
Payments (made) received to terminate hedge instruments				$ (13,700,000)
Number of terminated interest rate swap agreements | SwapAgreements			0	4
Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedge [Member] | Swap Agreement 3, Expires 2025 [Member]
Derivative [Line Items]
Notional amount of derivatives	50,000,000		$ 50,000,000
Derivative maturity expiration year			2025
Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedge [Member] | Swap Agreement 4, Expires 2026 [Member]
Derivative [Line Items]
Notional amount of derivatives	425,000,000		$ 425,000,000
Derivative maturity expiration year			2026
Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedge [Member] | Swap Agreement 5, Expires 2027 [Member]
Derivative [Line Items]
Notional amount of derivatives	825,000,000		$ 825,000,000
Derivative maturity expiration year			2027
Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedge [Member] | Swap Agreement 6, Expires 2028 [Member]
Derivative [Line Items]
Notional amount of derivatives	50,000,000		$ 50,000,000
Derivative maturity expiration year			2028
Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedge [Member] | Swap Agreement 7, Expires 2029 [Member]
Derivative [Line Items]
Notional amount of derivatives	75,000,000		$ 75,000,000
Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Fair Value Hedging [Member]
Derivative [Line Items]
Payments (made) received to terminate hedge instruments			$ 2,300,000
Number of terminated interest rate swap agreements | SwapAgreements			1	0
Interest Rate Swaps - Securities [Member] | Derivatives Designated as Hedging Instruments [Member] | Fair Value Hedging [Member]
Derivative [Line Items]
Notional amount of derivatives	397,500,000		$ 397,500,000		$ 477,500,000
Fair value hedges resulting net earnings	4,798,000	$ 3,215,000	13,398,000	$ 9,437,000
Derivative hedged item	374,400,000		374,400,000
Basis adjustment associated with hedged items loss	23,100,000		23,100,000
Interest Rate Swaps - Securities [Member] | Derivatives Designated as Hedging Instruments [Member] | Fair Value Hedging [Member] | Commercial Mortgage-Backed Securities [Member]
Derivative [Line Items]
Amortized cost basis of closed portfolio of pre-payable securities	$ 432,200,000		$ 432,200,000