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ACQUISITIONS - Supplemental Pro Forma Financial Information (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022
Business Acquisition |  |
Total revenue, net of interest expense | $ 687,976 | $ 646,375
Net income | 193,417 | $ 191,450
Elmira Savings Bank |  |
Business Acquisition |  |
Acquisitions-related expenses | $ 5,000 |

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