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LOANS AND ALLOWANCE FOR CREDIT LOSSES - Loan Portfolio (Details) - USD ($) $ in Thousands | Jun. 30, 2024 | Mar. 31, 2024 | Dec. 31, 2023 | Jun. 30, 2023 | Mar. 31, 2023 | Dec. 31, 2022
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Composition of loan portfolio [Abstract] |  |  |  |  |  |
Total loans, net of deferred loan fees and costs | $ 2,011,472 |  | $ 1,972,664 |  |  |
Allowance for credit losses | (21,031) | $ (20,471) | (22,517) | $ (20,172) | $ (20,075) | $ (19,659)
Loans, net | 1,990,441 |  | 1,950,147 |  |  |
Commercial Mortgages |  |  |  |  |  |
Composition of loan portfolio [Abstract] |  |  |  |  |  |
Total loans, net of deferred loan fees and costs | 1,154,712 |  | 1,122,925 |  |  |
Allowance for credit losses | (10,530) | (10,367) | (12,026) | (10,994) | (10,983) | (11,576)
Commercial Mortgages | Construction |  |  |  |  |  |
Composition of loan portfolio [Abstract] |  |  |  |  |  |
Total loans, net of deferred loan fees and costs | 146,369 |  | 138,887 |  |  |
Allowance for credit losses | 0 |  | 0 |  |  |
Commercial Mortgages | Commercial mortgages, other |  |  |  |  |  |
Composition of loan portfolio [Abstract] |  |  |  |  |  |
Total loans, net of deferred loan fees and costs | 1,008,343 |  | 984,038 |  |  |
Residential Mortgages |  |  |  |  |  |
Composition of loan portfolio [Abstract] |  |  |  |  |  |
Total loans, net of deferred loan fees and costs | 271,620 |  | 277,992 |  |  |
Allowance for credit losses | (2,106) | (2,062) | (2,194) | (1,905) | (1,892) | (1,845)
Consumer Loans |  |  |  |  |  |
Composition of loan portfolio [Abstract] |  |  |  |  |  |
Total loans, net of deferred loan fees and costs | 294,594 |  | 307,351 |  |  |
Allowance for credit losses | (3,501) | $ (3,526) | (3,242) | $ (3,152) | $ (3,147) | $ (2,865)
Consumer Loans | Home equity lines and loans |  |  |  |  |  |
Composition of loan portfolio [Abstract] |  |  |  |  |  |
Total loans, net of deferred loan fees and costs | 87,228 |  | 87,056 |  |  |
Consumer Loans | Indirect consumer loans |  |  |  |  |  |
Composition of loan portfolio [Abstract] |  |  |  |  |  |
Total loans, net of deferred loan fees and costs | 198,407 |  | 210,423 |  |  |
Consumer Loans | Direct consumer loans |  |  |  |  |  |
Composition of loan portfolio [Abstract] |  |  |  |  |  |
Total loans, net of deferred loan fees and costs | 8,959 |  | 9,872 |  |  |
Commercial and industrial |  |  |  |  |  |
Composition of loan portfolio [Abstract] |  |  |  |  |  |
Total loans, net of deferred loan fees and costs | $ 290,546 |  | $ 264,396 |  |  |

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