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Investment Securities - Narrative (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
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Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020
Debt Securities, Available-for-sale [Line Items] |  |  |  |
Proceeds from sale of available-for-sale investment securities | $ 232,000 | $ 0 | $ 257,524 | $ 0
Gain on the sale of available-for-sale investment securities | $ 300 |  | $ 253 | $ 0
Investment securities: |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |
Average percent of amortized cost for securities in unrealized loss positions for more than 12 months | 98.80% |  | 98.80% |

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