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Allowance for Credit Losses and Credit Quality of Loans, Allowance for Credit Losses on Off-Balance Sheet Credit Exposures (Details) - USD ($) $ in Thousands | Sep. 30, 2021 | Jun. 30, 2021 | Dec. 31, 2020 | Sep. 30, 2020 | Jun. 30, 2020 | Dec. 31, 2019
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Allowance for Credit Losses and Credit Quality of Loans [Abstract] |  |  |  |  |  |
Allowance for credit losses | $ 93,000 | $ 98,500 | $ 110,000 | $ 114,500 | $ 113,500 | $ 75,999
Unfunded Commitment [Member] |  |  |  |  |  |
Allowance for Credit Losses and Credit Quality of Loans [Abstract] |  |  |  |  |  |
Allowance for credit losses | $ 5,300 |  | $ 6,400 |  |  |

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