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Allowance for Credit Losses and Credit Quality of Loans, Summary (Details) - USD ($) $ in Thousands | 9 Months Ended | 12 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | ---
Sep. 30, 2024 | Dec. 31, 2023 | Jun. 30, 2024 | Sep. 30, 2023 | Aug. 11, 2023 | Jun. 30, 2023 | Dec. 31, 2022
Allowance for Credit Losses [Abstract] |  |  |  |  |  |  |
Allowance for credit losses | $ 119,500 | $ 114,400 | $ 120,500 | $ 114,601 |  | $ 100,400 |
Percentage of allowance of credit losses | 1.21% | 1.19% |  |  |  |  |
Forecast scenario weighting, baseline | 80.00% | 70.00% | 80.00% |  |  |  |
Forecast scenario weighting, downside | 20.00% | 30.00% | 20.00% |  |  |  |
Salisbury Bank [Member] |  |  |  |  |  |  |
Allowance for Credit Losses [Abstract] |  |  |  |  |  |  |
Loans purchased with credit deterioration | $ 0 | $ 219,500 |  |  |  |  |
Allowance for credit losses on loans purchased |  | 5,800 |  |  |  |  |
Allowance for credit losses at acquisition |  |  |  |  | $ 14,500 |  |
Salisbury Bank [Member] | PCD [Member] |  |  |  |  |  |  |
Allowance for Credit Losses [Abstract] |  |  |  |  |  |  |
Allowance for credit losses at acquisition |  |  |  |  | 5,800 |  |
Salisbury Bank [Member] | Non-PCD [Member] |  |  |  |  |  |  |
Allowance for Credit Losses [Abstract] |  |  |  |  |  |  |
Allowance for credit losses at acquisition |  |  |  |  | $ 8,800 |  |
ASU 2022-02 [Member] |  |  |  |  |  |  |
Allowance for Credit Losses [Abstract] |  |  |  |  |  |  |
Allowance for credit losses |  |  |  | 114,601 |  |  | $ 100,152
Loans [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member] | ASU 2022-02 [Member] |  |  |  |  |  |  |
Allowance for Credit Losses [Abstract] |  |  |  |  |  |  |
Allowance for credit losses |  |  |  |  |  |  | (600)
Accrued Interest Receivable [Member] |  |  |  |  |  |  |
Allowance for Credit Losses [Abstract] |  |  |  |  |  |  |
Allowance for credit losses | 0 | 0 |  |  |  |  |
AIR on loans | $ 34,200 | $ 34,100 |  |  |  |  |
Financing Receivable, Accrued Interest, after Allowance for Credit Loss, Statement of Financial Position [Extensible Enumeration] | Other Assets | Other Assets |  |  |  |  |
Residential [Member] |  |  |  |  |  |  |
Allowance for Credit Losses [Abstract] |  |  |  |  |  |  |
Allowance for credit losses | $ 26,646 | $ 22,070 | $ 25,874 | 20,607 |  | $ 15,554 |
Amount of loans purchased | $ 2,000 | $ 3,800 |  |  |  |  |
Premium on loans purchased | 7.00% | 7.00% |  |  |  |  |
Allowance for credit losses on loans purchased | $ 20 | $ 31 |  |  |  |  |
Residential [Member] | ASU 2022-02 [Member] |  |  |  |  |  |  |
Allowance for Credit Losses [Abstract] |  |  |  |  |  |  |
Allowance for credit losses |  |  |  | $ 20,607 |  |  | $ 14,539

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