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Investment Securities (Narrative) (Details)
 3 Months Ended 9 Months Ended
Dec. 13, 2024
USD ($)
Sep. 30, 2025
USD ($)
Security
Sep. 30, 2024
USD ($)
Sep. 30, 2025
USD ($)
Security
Sep. 30, 2024
USD ($)
Dec. 31, 2024
USD ($)
Security
Schedule Of Investments [Line Items]            
Securities pledged as collateral   $ 939,700,000   $ 939,700,000   $ 828,800,000
Proceeds from Sale of Debt Securities, Available-for-Sale   $ 29,186,000 $ 0 $ 94,142,000 $ 0  
Proceeds from sales used to fund losses $ 653,500,000          
Pre-tax loss 100,200,000          
Number of security positions, unrealized loss position | Security   52   52   76
Number of security positions, unrealized loss position for more than 12 months | Security   37   37   37
Securities, 12 months or longer, Fair Value   $ 206,249,000   $ 206,249,000   $ 176,627,000
Securities, 12 months or longer, Unrealized Losses   $ 45,753,000   $ 45,753,000   $ 53,433,000
Number of security positions, unrealized loss position for less than 12 months | Security   15   15   39
Securities, Less than 12 months, Fair Value   $ 148,933,000   $ 148,933,000   $ 681,223,000
Securities, Less than 12 months, Unrealized Losses   2,684,000   2,684,000   9,046,000
Available for sale securities, allowance for credit loss   0   0   0
Securities held to maturity, Amortized Cost   87,627,000   87,627,000   116,003,000
Internally rated held-to-maturity securities   $ 4,700,000   $ 4,700,000   $ 3,400,000
Investment, Type [Extensible Enumeration]   Municipal Bonds [Member]   Municipal Bonds [Member]   Municipal Bonds [Member]
Investment securities, past due   $ 4,590,423,000   $ 4,590,423,000   $ 4,479,204,000
Higher-Yielding Agency Wrapped Investments [Member]            
Schedule Of Investments [Line Items]            
Net proceeds from sale of securities to purchase investment $ 642,600,000          
Total Past Due [Member]            
Schedule Of Investments [Line Items]            
Investment securities, past due   19,222,000   19,222,000   22,030,000
Municipal Bonds [Member]            
Schedule Of Investments [Line Items]            
Securities held to maturity, Amortized Cost   29,100,000   29,100,000   41,900,000
Available for Sale Securities [Member]            
Schedule Of Investments [Line Items]            
Accrued interest receivable   3,500,000   3,500,000   3,400,000
Held To Maturity Investment Securities [Member]            
Schedule Of Investments [Line Items]            
Accrued interest receivable   447,000   447,000   456,000
Held To Maturity Investment Securities [Member] | Total Past Due [Member]            
Schedule Of Investments [Line Items]            
Investment securities, past due   0   0   $ 0
Held To Maturity Investment Securities [Member] | Maximum [Member]            
Schedule Of Investments [Line Items]            
Provision for credit loss   $ 1,000 $ 1,000 $ 1,000 $ 1,000