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Investment Securities (Narrative) (Details) | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2020 USD ($) Security | Sep. 30, 2019 USD ($) | Sep. 30, 2020 USD ($) Security | Sep. 30, 2019 USD ($) | Dec. 31, 2019 USD ($) Security
Schedule Of Investments [Line Items] |  |  |  |  |
Securities pledged as collateral | $ 634,400,000 |  | $ 634,400,000 |  | $ 676,900,000
Number of security positions, unrealized loss position | Security | 16 |  | 16 |  | 91
Number of security positions, unrealized loss position for more than 12 months | Security | 1 |  | 1 |  | 34
Securities, 12 months or longer, Fair Value | $ 8,000 |  | $ 8,000 |  | $ 47,202,000
Securities, 12 months or longer, Unrealized Losses |  |  |  |  | $ 659,000
Number of security positions, unrealized loss position for less than 12 months | Security | 15 |  | 15 |  | 57
Securities, less than 12 months, Fair Value | $ 83,178,000 |  | $ 83,178,000 |  | $ 178,723,000
Securities, less than 12 months, Unrealized Losses | 206,000 |  | 206,000 |  | 1,595,000
Available for sale securities, allowance for credit loss | 0 |  | 0 |  |
Debt securities, held-to-maturity | 290,954,000 |  | 290,954,000 |  | 359,000,000
Investment securities, past due | 5,226,000 |  | 5,226,000 |  | 7,081,000
Investment securities, nonaccrual | 10,762,000 |  | 10,762,000 |  | 8,634,000
Municipal Bonds [Member] |  |  |  |  |
Schedule Of Investments [Line Items] |  |  |  |  |
Debt securities, held-to-maturity | 151,600,000 |  | 151,600,000 |  |
Internally rated held-to-maturity securities | 8,500,000 |  | 8,500,000 |  |
Municipal Bonds [Member] | Below Investment Grade [Member] |  |  |  |  |
Schedule Of Investments [Line Items] |  |  |  |  |
Investment grade rating exposure | 279,000 |  | $ 279,000 |  |
Investment grade rating exposure percentage |  |  | 0.18% |  |
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 | 1,000,000.0 |  | 1,000,000.0 |  | 1,000,000.0
Held To Maturity Investment Securities [Member] |  |  |  |  |
Schedule Of Investments [Line Items] |  |  |  |  |
Accrued interest receivable | 1,400,000 |  | 1,400,000 |  | $ 1,200,000
Credit loss expense | 0 | $ 0 | (6,000) | $ 0 |
Investment securities, past due | 0 |  | 0 |  |
Investment securities, nonaccrual | $ 0 |  | $ 0 |  |

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