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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) |

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