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Investment Securities (Narrative) (Details)
 3 Months Ended 12 Months Ended
Mar. 31, 2021
USD ($)
Security
Mar. 31, 2020
USD ($)
Dec. 31, 2020
USD ($)
Security
Schedule Of Investments [Line Items]      
Securities pledged as collateral $ 660,100,000   $ 567,400,000
Number of security positions, unrealized loss position | Security 62   8
Number of security positions, unrealized loss position for more than 12 months | Security 1   1
Securities, 12 months or longer, Fair Value $ 13,000   $ 8,000
Number of security positions, unrealized loss position for less than 12 months | Security 61   7
Securities, less than 12 months, Fair Value $ 465,673,000   $ 29,087,000
Securities, less than 12 months, Unrealized Losses 10,442,000   68,000
Available for sale securities, allowance for credit loss 0   0
Debt securities, held-to-maturity 256,134,000   271,973,000
Investment securities, past due 2,454,000   7,994,000
Investment securities, nonaccrual 9,404,000   9,286,000
Municipal Bonds [Member]      
Schedule Of Investments [Line Items]      
Debt securities, held-to-maturity 131,400,000   135,700,000
Internally rated held-to-maturity securities 7,600,000   8,500,000
Municipal Bonds [Member] | Below Investment Grade [Member]      
Schedule Of Investments [Line Items]      
Investment grade rating exposure $ 280,000   $ 279,000
Investment grade rating exposure percentage 0.20%   0.19%
Maximum [Member]      
Schedule Of Investments [Line Items]      
Securities, 12 months or longer, Unrealized Losses $ 1,000   $ 1,000
Available for Sale Securities [Member]      
Schedule Of Investments [Line Items]      
Accrued interest receivable 1,400,000   1,200,000
Held To Maturity Investment Securities [Member]      
Schedule Of Investments [Line Items]      
Accrued interest receivable 1,300,000   905,000
Investment securities, past due 0   0
Investment securities, nonaccrual 0   $ 0
Held To Maturity Investment Securities [Member] | Maximum [Member]      
Schedule Of Investments [Line Items]      
Credit loss expense $ (1,000) $ (1,000)