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Investment Securities (Narrative) (Details)
 3 Months Ended 9 Months Ended
Sep. 30, 2023
USD ($)
Security
Sep. 30, 2022
USD ($)
Sep. 30, 2023
USD ($)
Security
Sep. 30, 2022
USD ($)
Dec. 31, 2022
USD ($)
Security
Schedule Of Investments [Line Items]          
Securities pledged as collateral $ 786,700,000   $ 786,700,000   $ 850,400,000
Number of security positions, unrealized loss position | Security 219   219   226
Number of security positions, unrealized loss position for more than 12 months | Security 215   215   127
Securities, 12 months or longer, Fair Value $ 853,876,000   $ 853,876,000   $ 760,210,000
Securities, 12 months or longer, Unrealized Losses $ 207,291,000   $ 207,291,000   $ 155,102,000
Number of security positions, unrealized loss position for less than 12 months | Security 4   4   99,000,000
Securities, Less than 12 months, Fair Value $ 14,000   $ 14,000   $ 193,800,000
Securities, Less than 12 months, Unrealized Losses 0   0   17,922,000
Available for sale securities, allowance for credit loss 0   0   0
Securities held to maturity, Amortized Cost 154,208,000   154,208,000   188,980,000
Investment securities, past due 4,382,760,000   4,382,760,000   3,998,718,000
Investment securities, nonaccrual 9,515,000   9,515,000   10,197,000
Total Past Due [Member]          
Schedule Of Investments [Line Items]          
Investment securities, past due 28,350,000   28,350,000   16,709,000
Municipal Bonds [Member]          
Schedule Of Investments [Line Items]          
Securities held to maturity, Amortized Cost 68,200,000   68,200,000   90,600,000
Internally rated held-to-maturity securities 3,800,000   3,800,000   6,900,000
Held To Maturity Securities Non Rated 700,000   700,000    
Maximum [Member]          
Schedule Of Investments [Line Items]          
Securities, 12 months or longer, Unrealized Losses 207,300,000   207,300,000   155,100,000
Securities, Less than 12 months, Unrealized Losses 1,000   1,000    
Available for Sale Securities [Member]          
Schedule Of Investments [Line Items]          
Accrued interest receivable 1,900,000   1,900,000   2,100,000
Held To Maturity Investment Securities [Member]          
Schedule Of Investments [Line Items]          
Accrued interest receivable 847,000   847,000   695,000
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