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Investment Securities - Narrative (Details) $ in Thousands | Sep. 30, 2021 USD ($) instrument | Jan. 01, 2021 USD ($) | Dec. 31, 2020 USD ($)
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Schedule of Available for sale Securities and Held to maturity Securities [Line Items] |  |  |
Accrued interest on investment securities | $ 22,800 |  |
Allowance for credit losses | 245 |  | $ 0
Gross unrealized losses | 16,161 |  | 349
Carrying value of securities pledged as collateral | 946,200 |  | 890,000
Securities sold under repurchase agreements | 176,700 |  | 167,300
State and municipal |  |  |
Schedule of Available for sale Securities and Held to maturity Securities [Line Items] |  |  |
Allowance for credit losses | 245 |  | 0
Gross unrealized losses | $ 3,946 |  | 246
Number of securities in unrealized loss positions | instrument | 179 |  |
State and municipal | Cumulative effect of ASC 326 adoption |  |  |
Schedule of Available for sale Securities and Held to maturity Securities [Line Items] |  |  |
Allowance for credit losses |  | $ 245 | 245
U.S. Government-sponsored mortgage-backed securities |  |  |
Schedule of Available for sale Securities and Held to maturity Securities [Line Items] |  |  |
Allowance for credit losses | $ 0 |  | 0
Gross unrealized losses | $ 12,215 |  | $ 103
Number of securities in unrealized loss positions | instrument | 49 |  |

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