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LOANS AND ALLOWANCE FOR CREDIT LOSSES - Allowance for Credit Losses (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Allowance for credit loss - loans |  |  |
Beginning balance | $ 61,059 | $ 50,672 |
Charge-offs | (784) |  | $ (8,965)
Recoveries |  |  | 6,118
Provision |  |  | (8,153)
Ending balance | 66,669 | 61,059 | 50,672
Accrued interest receivable on loans | $ 31,200 | $ 25,100 |
Financing Receivable, Accrued Interest, after Allowance for Credit Loss, Statement of Financial Position [Extensible Enumeration] | Interest Receivable | Interest Receivable |
Purchase of loans |  | $ 436,900 |
Amount pledged | $ 9,637,929 | 8,748,335 |
Amounts outstanding | 406,900 |  |
Foreclosures in progress | 5,800 | 3,500 |
Sale of secondary market eligible residential consumer mortgage loans | 6,100 | 5,300 |
Provision | 11,203 | 14,773 | (8,839)
Liabilities for off-balance-sheet |  |  |
Beginning balance | 1,123 | 803 |
Charge-offs | 0 | 0 | 0
Recoveries | 0 | 0 | 0
PCD Allowance at Acquisition |  | 0 |
Provision | (210) |  | (686)
Ending balance | 913 | 1,123 | 803
Allowance for credit loss |  |  |
Beginning balance |  | 49,869 |
Charge-offs |  |  | (8,965)
Recoveries |  |  | 6,118
Provision |  |  | (8,839)
Ending balance |  |  | 49,869
Assets pledged as collateral | Borrowings from FHLB and FRB |  |  |
Allowance for credit loss - loans |  |  |
Amount pledged | 4,390,000 |  |
Topic ASC 326 [Member] |  |  |
Liabilities for off-balance-sheet |  |  |
Provision |  | 320 |
Elmira Savings Bank ("Elmira") |  |  |
Allowance for credit loss - loans |  |  |
Beginning balance | 61,100 |  |
Ending balance | 66,700 | 61,100 |
Commercial Loan |  |  |
Allowance for credit loss - loans |  |  |
Purchase of loans |  | 125,300 |
Consumer indirect |  |  |
Allowance for credit loss - loans |  |  |
Charge-offs | (9,352) |  |
Purchase of loans |  | 9,400 |
Consumer direct |  |  |
Allowance for credit loss - loans |  |  |
Charge-offs | (2,009) |  |
Purchase of loans |  | 12,500 |
Home equity |  |  |
Allowance for credit loss - loans |  |  |
Charge-offs | (119) |  |
Purchase of loans |  | 18,300 |
Consumer mortgage |  |  |
Allowance for credit loss - loans |  |  |
Charge-offs | (669) |  |
Purchase of loans |  | 271,400 |
Unallocated |  |  |
Allowance for credit loss - loans |  |  |
Beginning balance |  | 1,000 |
Charge-offs |  |  | 0
Recoveries |  |  | 0
Provision |  |  | 0
Ending balance |  |  | 1,000
Commercial Portfolio Segment |  |  |
Allowance for credit loss - loans |  |  |
Beginning balance |  |  | 62,358
Liabilities for off-balance-sheet |  |  |
Beginning balance |  |  | 1,489
Allowance for credit loss |  |  |
Beginning balance |  |  | 60,869
Commercial Portfolio Segment | Commercial Loan |  |  |
Allowance for credit loss - loans |  |  |
Beginning balance | 23,297 | 22,995 | 30,072
Charge-offs |  |  | (1,922)
Recoveries |  |  | 796
Provision |  |  | (5,951)
Ending balance |  | 23,297 | 22,995
Allowance for credit loss |  |  |
Charge-offs |  | (824) |
Recoveries |  | 1,374 |
PCD Allowance at Acquisition |  | 71 |
Commercial Portfolio Segment | Commercial Loan | Topic ASC 326 [Member] |  |  |
Allowance for credit loss - loans |  |  |
Provision |  | (319) |
Commercial Portfolio Segment | Unallocated |  |  |
Allowance for credit loss - loans |  |  |
Beginning balance |  |  | 1,000
Residential Portfolio Segment | Home equity |  |  |
Allowance for credit loss - loans |  |  |
Beginning balance | 1,594 | 1,814 | 2,222
Charge-offs | (119) | (86) | (225)
Recoveries | 14 | 163 | 92
Provision | 139 |  | (275)
Ending balance | 1,628 | 1,594 | 1,814
Allowance for credit loss |  |  |
PCD Allowance at Acquisition |  | 0 |
Residential Portfolio Segment | Home equity | Topic ASC 326 [Member] |  |  |
Allowance for credit loss - loans |  |  |
Provision |  | (297) |
Residential Portfolio Segment | Consumer mortgage |  |  |
Allowance for credit loss - loans |  |  |
Beginning balance | 14,343 | 10,017 | 10,672
Charge-offs | (669) | (313) | (426)
Recoveries | 48 | 62 | 91
Provision | 1,611 |  | (320)
Ending balance | 15,333 | 14,343 | 10,017
Allowance for credit loss |  |  |
PCD Allowance at Acquisition |  | 0 |
Residential Portfolio Segment | Consumer mortgage | Topic ASC 326 [Member] |  |  |
Allowance for credit loss - loans |  |  |
Provision |  | 4,577 |
Consumer Portfolio Segment | Commercial Loan |  |  |
Allowance for credit loss - loans |  |  |
Beginning balance | 23,297 |  |
Charge-offs | (784) |  |
Recoveries | 523 |  |
Provision | 3,818 |  |
Ending balance | 26,854 | 23,297 |
Consumer Portfolio Segment | Consumer indirect |  |  |
Allowance for credit loss - loans |  |  |
Beginning balance | 17,852 | 11,737 | 13,696
Charge-offs | (9,352) | (7,986) | (5,160)
Recoveries | 5,719 | 4,756 | 4,346
Provision | 4,366 |  | (1,145)
Ending balance | 18,585 | 17,852 | 11,737
Allowance for credit loss |  |  |
PCD Allowance at Acquisition |  | 0 |
Consumer Portfolio Segment | Consumer indirect | Topic ASC 326 [Member] |  |  |
Allowance for credit loss - loans |  |  |
Provision |  | 9,345 |
Consumer Portfolio Segment | Consumer direct |  |  |
Allowance for credit loss - loans |  |  |
Beginning balance | 2,973 | 2,306 | 3,207
Charge-offs | (2,009) | (1,252) | (1,232)
Recoveries | 826 | 772 | 793
Provision | 1,479 |  | (462)
Ending balance | 3,269 | 2,973 | 2,306
Allowance for credit loss |  |  |
PCD Allowance at Acquisition |  | 0 |
Consumer Portfolio Segment | Consumer direct | Topic ASC 326 [Member] |  |  |
Allowance for credit loss - loans |  |  |
Provision |  | 1,147 |
Unallocated |  |  |
Allowance for credit loss - loans |  |  |
Beginning balance | 1,000 | 1,000 |
Charge-offs | 0 | 0 |
Recoveries | 0 | 0 |
Provision | 0 |  |
Ending balance | 1,000 | 1,000 | 1,000
Allowance for credit loss |  |  |
PCD Allowance at Acquisition |  | 0 |
Unallocated | Topic ASC 326 [Member] |  |  |
Allowance for credit loss - loans |  |  |
Provision |  | 0 |
Allowances For Credit Losses [Member] |  |  |
Allowance for credit loss |  |  |
Beginning balance | 61,059 | 49,869 |
Charge-offs | (12,933) | (10,461) |
Recoveries | 7,130 | 7,127 |
PCD Allowance at Acquisition |  | 71 |
Provision | 11,413 |  |
Ending balance | 66,669 | 61,059 | 49,869
Allowances For Credit Losses [Member] | Topic ASC 326 [Member] |  |  |
Allowance for credit loss |  |  |
Provision |  | 14,453 |
Total Allowances For Credit Losses [Member] |  |  |
Allowance for credit loss - loans |  |  |
Beginning balance | 62,182 | 50,672 |
Charge-offs | (12,933) | (10,461) |
Recoveries | 7,130 | 7,127 |
Provision | 11,203 |  |
Ending balance | $ 67,582 | 62,182 | $ 50,672
Allowance for credit loss |  |  |
PCD Allowance at Acquisition |  | 71 |
Total Allowances For Credit Losses [Member] | Topic ASC 326 [Member] |  |  |
Allowance for credit loss - loans |  |  |
Provision |  | $ 14,773 |

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