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INVESTMENT SECURITIES (Tables) | 9 Months Ended
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Sep. 30, 2024
INVESTMENT SECURITIES |
Schedule of amortized cost and estimated fair value of investment securities | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | September 30, 2024 | ​ | December 31, 2023
​ | ​ | ​ | ​ | ​ | Gross | ​ | Gross | ​ | ​ | ​ | ​ | ​ | ​ | ​ | Gross | ​ | Gross | ​ | ​ | ​
​ | ​ | Amortized | ​ | Unrealized | ​ | Unrealized | ​ | Fair | ​ | Amortized | ​ | Unrealized | ​ | Unrealized | ​ | Fair
(000’s omitted) |  | Cost |  | Gains |  | Losses |  | Value |  | Cost |  | Gains |  | Losses |  | Value
Available-for-Sale Portfolio: | ​ | ​ | ​ |  | ​ |  |  | ​ |  | ​ | ​ | ​ | ​ | ​ | ​ |  | ​ |  |  | ​ |  | ​ | ​ | ​
U.S. Treasury and agency securities | ​ | $ | 2,386,644 | ​ | $ | 0 | ​ | $ | 244,022 | ​ | $ | 2,142,622 | ​ | $ | 2,381,168 | ​ | $ | 0 | ​ | $ | 300,385 | ​ | $ | 2,080,783
Obligations of state and political subdivisions | ​ |  | 430,699 | ​ |  | 878 | ​ |  | 29,625 | ​ |  | 401,952 | ​ |  | 502,879 | ​ |  | 1,469 | ​ |  | 29,985 | ​ |  | 474,363
Government agency mortgage-backed securities | ​ |  | 370,845 | ​ |  | 116 | ​ |  | 44,452 | ​ |  | 326,509 | ​ |  | 400,062 | ​ |  | 76 | ​ |  | 51,612 | ​ |  | 348,526
Corporate debt securities | ​ |  | 8,000 | ​ |  | 0 | ​ |  | 327 | ​ |  | 7,673 | ​ |  | 8,000 | ​ |  | 0 | ​ |  | 606 | ​ |  | 7,394
Government agency collateralized mortgage obligations | ​ |  | 7,506 | ​ |  | 0 | ​ |  | 319 | ​ |  | 7,187 | ​ |  | 9,498 | ​ |  | 0 | ​ |  | 572 | ​ |  | 8,926
Total available-for-sale portfolio | ​ | $ | 3,203,694 | ​ | $ | 994 | ​ | $ | 318,745 | ​ | $ | 2,885,943 | ​ | $ | 3,301,607 | ​ | $ | 1,545 | ​ | $ | 383,160 | ​ | $ | 2,919,992
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Held-to-Maturity Portfolio: | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
U.S. Treasury and agency securities | ​ | $ | 1,131,278 | ​ | $ | 0 | ​ | $ | 43,848 | ​ | $ | 1,087,430 | ​ | $ | 1,109,101 | ​ | $ | 0 | ​ | $ | 50,866 | ​ | $ | 1,058,235
Government agency mortgage-backed securities | ​ | ​ | 187,772 | ​ | ​ | 1,817 | ​ | ​ | 343 | ​ | ​ | 189,246 | ​ | ​ | 63,073 | ​ | ​ | 688 | ​ | ​ | 180 | ​ | ​ | 63,581
Total held-to-maturity portfolio | ​ | $ | 1,319,050 | ​ | $ | 1,817 | ​ | $ | 44,191 | ​ | $ | 1,276,676 | ​ | $ | 1,172,174 | ​ | $ | 688 | ​ | $ | 51,046 | ​ | $ | 1,121,816
Schedule of gains and losses on equity and other securities | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Three Months Ended | ​ | Nine Months Ended
​ | ​ | September 30, | ​ | September 30,
(000’s omitted) |  | 2024 |  | 2023 |  | 2024 |  | 2023
Net gain (loss) recognized on equity securities | ​ | $ | 101 | ​ | $ | (49) | ​ | $ | 984 | ​ | $ | (99)
Less: Net gain (loss) recognized on equity securities sold during the period | ​ |  | 0 | ​ |  | 0 | ​ |  | 0 | ​ |  | 0
Unrealized gain (loss) recognized on equity securities still held | ​ | $ | 101 | ​ | $ | (49) | ​ | $ | 984 | ​ | $ | (99)
Schedule of investment securities that have been in a continuous unrealized loss position | As of September 30, 2024 ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Less than 12 Months |  | 12 Months or Longer |  | Total
​ | ​ | ​ | ​ | ​ | Gross | ​ | ​ | ​ | ​ | Gross | ​ | ​ | ​ | ​ | Gross
​ | ​ | Fair | ​ | Unrealized | ​ | Fair | ​ | Unrealized | ​ | Fair | ​ | Unrealized
(000’s omitted) |  | Value |  | Losses |  | Value |  | Losses |  | Value |  | Losses
Available-for-Sale Portfolio: | ​ | ​ |  | ​ | ​ |  | ​ | ​ |  | ​ | ​ |  | ​ | ​ | ​ | ​ | ​ |
U.S. Treasury and agency securities | ​ | $ | 0 | ​ | $ | 0 | ​ | $ | 2,142,622 | ​ | $ | 244,022 | ​ | $ | 2,142,622 | ​ | $ | 244,022
Obligations of state and political subdivisions | ​ |  | 19,552 | ​ |  | 83 | ​ |  | 302,843 | ​ |  | 29,542 | ​ |  | 322,395 | ​ |  | 29,625
Government agency mortgage-backed securities | ​ |  | 23 | ​ |  | 0 | ​ |  | 315,368 | ​ |  | 44,452 | ​ |  | 315,391 | ​ |  | 44,452
Corporate debt securities | ​ | ​ | 0 | ​ | ​ | 0 | ​ | ​ | 7,673 | ​ | ​ | 327 | ​ | ​ | 7,673 | ​ | ​ | 327
Government agency collateralized mortgage obligations | ​ |  | 0 | ​ |  | 0 | ​ |  | 7,174 | ​ |  | 319 | ​ |  | 7,174 | ​ |  | 319
Total available-for-sale investment portfolio | ​ | $ | 19,575 | ​ | $ | 83 | ​ | $ | 2,775,680 | ​ | $ | 318,662 | ​ | $ | 2,795,255 | ​ | $ | 318,745
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Held-to-Maturity Portfolio: | ​ |  | ​ | ​ |  |  |  |  |  | ​ |  |  |  |  |  | ​ |  | ​
U.S Treasury and agency securities | ​ | $ | 0 | ​ | $ | 0 | ​ | $ | 1,087,430 | ​ | $ | 43,848 | ​ | $ | 1,087,430 | ​ | $ | 43,848
Government agency mortgage-backed securities | ​ | ​ | 61,169 | ​ | ​ | 334 |  | ​ | 1,382 | ​ | ​ | 9 |  | ​ | 62,551 | ​ | ​ | 343
Total held-to-maturity portfolio | ​ | $ | 61,169 | ​ | $ | 334 |  | $ | 1,088,812 | ​ | $ | 43,857 |  | $ | 1,149,981 | ​ | $ | 44,191
​ As of December 31, 2023 ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Less than 12 Months |  | 12 Months or Longer |  | Total
​ | ​ | ​ | ​ | ​ | Gross | ​ | ​ | ​ | ​ | Gross | ​ | ​ | ​ | ​ | Gross
​ | ​ | Fair | ​ | Unrealized | ​ | Fair | ​ | Unrealized | ​ | Fair | ​ | Unrealized
(000’s omitted) |  | Value |  | Losses |  | Value |  | Losses |  | Value |  | Losses
Available-for-Sale Portfolio: | ​ | ​ |  | ​ | ​ |  | ​ | ​ |  | ​ | ​ |  | ​ | ​ |  | ​ | ​ |
U.S. Treasury and agency securities | ​ | $ | 0 | ​ | $ | 0 | ​ | $ | 2,080,783 | ​ | $ | 300,385 | ​ | $ | 2,080,783 | ​ | $ | 300,385
Obligations of state and political subdivisions | ​ |  | 63,541 | ​ |  | 878 | ​ |  | 287,191 | ​ |  | 29,107 | ​ |  | 350,732 | ​ |  | 29,985
Government agency mortgage-backed securities | ​ |  | 8,586 | ​ |  | 55 | ​ |  | 336,266 | ​ |  | 51,557 | ​ |  | 344,852 | ​ |  | 51,612
Corporate debt securities | ​ | ​ | 0 | ​ | ​ | 0 | ​ | ​ | 7,394 | ​ | ​ | 606 | ​ | ​ | 7,394 | ​ | ​ | 606
Government agency collateralized mortgage obligations | ​ |  | 0 | ​ |  | 0 | ​ |  | 8,907 | ​ |  | 572 | ​ |  | 8,907 | ​ |  | 572
Total available-for-sale investment portfolio | ​ | $ | 72,127 | ​ | $ | 933 | ​ | $ | 2,720,541 | ​ | $ | 382,227 | ​ | $ | 2,792,668 | ​ | $ | 383,160
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Held-to-Maturity Portfolio: | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
U.S Treasury and agency securities | ​ | $ | 536,885 | ​ | $ | 15,953 | ​ | $ | 521,350 | ​ | $ | 34,913 | ​ | $ | 1,058,235 | ​ | $ | 50,866
Government agency mortgage-backed securities | ​ | ​ | 18,951 | ​ | ​ | 158 | ​ | ​ | 1,393 | ​ | ​ | 22 | ​ | ​ | 20,344 | ​ | ​ | 180
Total held-to-maturity portfolio | ​ | $ | 555,836 | ​ | $ | 16,111 | ​ | $ | 522,743 | ​ | $ | 34,935 | ​ | $ | 1,078,579 | ​ | $ | 51,046
Schedule of amortized cost and estimated fair value of debt securities by contractual maturity | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Held-to-Maturity | ​ | Available-for-Sale
​ | ​ | Amortized | ​ | Fair | ​ | Amortized | ​ | Fair
(000’s omitted) |  | Cost |  | Value |  | Cost |  | Value
Due in one year or less | ​ | $ | 0 | ​ | $ | 0 | ​ | $ | 10,716 | ​ | $ | 10,654
Due after one through five years | ​ |  | 0 | ​ |  | 0 | ​ | ​ | 1,892,504 | ​ | ​ | 1,766,022
Due after five years through ten years | ​ |  | 562,638 | ​ |  | 553,223 | ​ | ​ | 268,172 | ​ | ​ | 244,929
Due after ten years | ​ |  | 568,640 | ​ |  | 534,207 | ​ | ​ | 653,951 | ​ | ​ | 530,642
Subtotal | ​ |  | 1,131,278 | ​ |  | 1,087,430 | ​ | ​ | 2,825,343 | ​ | ​ | 2,552,247
Government agency mortgage-backed securities | ​ |  | 187,772 | ​ |  | 189,246 | ​ | ​ | 370,845 | ​ | ​ | 326,509
Government agency collateralized mortgage obligations | ​ |  | 0 | ​ |  | 0 | ​ | ​ | 7,506 | ​ | ​ | 7,187
Total | ​ | $ | 1,319,050 | ​ | $ | 1,276,676 | ​ | $ | 3,203,694 | ​ | $ | 2,885,943

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