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Derivatives (Narrative) (Details)
 3 Months Ended
Mar. 31, 2026
USD ($)
SwapAgreements
Mar. 31, 2025
USD ($)
SwapAgreements
Dec. 31, 2025
USD ($)
Derivative [Line Items]      
Notional amount of derivatives $ 8,315,062,000   $ 8,040,346,000
Payments (made) received to terminate hedge instruments 1,657,000    
Fair value hedges resulting net earnings [1] 47,167,000 $ (4,517,000)  
Fair value liability 1,100,000   1,300,000
Credit risk-related contingent features, net liability position 13,200,000   13,200,000
Credit risk-related contingent features, posted collateral 13,600,000   13,000,000
Fair Value Hedging [Member]      
Derivative [Line Items]      
Notional amount of derivatives 265,000,000 $ 125,000,000  
Derivatives Designated as Hedging Instruments [Member]      
Derivative [Line Items]      
Notional amount of derivatives 2,159,000,000   2,172,500,000
Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedge [Member] | Swap Agreement 3, Expires 2026 [Member]      
Derivative [Line Items]      
Notional amount of derivatives $ 350,000,000    
Derivative maturity expiration year 2026    
Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedge [Member] | Swap Agreement 4, Expires 2027 [Member]      
Derivative [Line Items]      
Notional amount of derivatives $ 825,000,000    
Derivative maturity expiration year 2027    
Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedge [Member] | Swap Agreement 5, Expires 2028 [Member]      
Derivative [Line Items]      
Notional amount of derivatives $ 50,000,000    
Derivative maturity expiration year 2028    
Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedge [Member] | Swap Agreement 6, Expires 2029 [Member]      
Derivative [Line Items]      
Notional amount of derivatives $ 275,000,000    
Derivative maturity expiration year 2029    
Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedge [Member] | Swap Agreement 7, Expires 2030 [Member]      
Derivative [Line Items]      
Notional amount of derivatives $ 300,000,000    
Derivative maturity expiration year 2030    
Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Fair Value Hedging [Member]      
Derivative [Line Items]      
Payments (made) received to terminate hedge instruments $ 1,700,000    
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 $ 359,000,000   $ 397,500,000
Fair value hedges resulting net earnings [1] 1,674,000 $ 3,910,000  
Derivative hedged item 335,600,000    
Basis adjustment associated with hedged items loss 23,400,000    
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 $ 387,800,000    
[1] Includes the effects of both active derivative instruments and the impact from realization of basis adjustments to hedged assets resulting from previously terminated hedges.