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SECURITIES (Tables) | 12 Months Ended
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Dec. 31, 2023
SECURITIES |
Schedule of major categories of securities owned by entity | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | December 31, 2023
​ | ​ | ​ | ​ | ​ | Gross | ​ | Gross | ​ | ​ | ​
​ | ​ | Amortized | ​ | Unrealized | ​ | Unrealized | ​ | Fair
(In thousands) |  | Cost |  | Gains |  | Losses |  | Value
Securities available-for-sale: |  | ​ |  |  | ​ |  |  | ​ |  |  | ​ |
Agency notes | ​ | $ | 10,000 | ​ | $ | — | ​ | $ | (629) | ​ | $ | 9,371
Treasury securities | ​ | ​ | 245,877 | ​ | ​ | — | ​ | ​ | (11,687) | ​ | ​ | 234,190
Corporate securities | ​ |  | 174,978 | ​ |  | — | ​ |  | (23,808) | ​ |  | 151,170
Pass-through mortgage-backed securities ("MBS") issued by government sponsored entities ("GSEs") | ​ |  | 230,253 | ​ |  | 10 | ​ |  | (24,978) | ​ |  | 205,285
Agency CMOs | ​ |  | 305,860 | ​ |  | 46 | ​ |  | (46,491) | ​ |  | 259,415
State and municipal obligations | ​ | ​ | 28,741 | ​ | ​ | — | ​ | ​ | (1,932) | ​ | ​ | 26,809
Total securities available-for-sale | ​ | $ | 995,709 | ​ | $ | 56 | ​ | $ | (109,525) | ​ | $ | 886,240
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | December 31, 2023
​ | ​ | ​ | ​ | ​ | Gross | ​ | Gross | ​ | ​ | ​
​ | ​ | Amortized | ​ | Unrecognized | ​ | Unrecognized | ​ | Fair
(In thousands) |  | Cost |  | Gains |  | Losses |  | Value
Securities held-to-maturity: |  | ​ |  |  | ​ |  |  | ​ |  |  | ​ |
Agency notes | ​ | $ | 89,563 | ​ | $ | — | ​ | $ | (11,300) | ​ | $ | 78,263
Corporate securities | ​ | ​ | 9,000 | ​ | ​ | — | ​ | ​ | (1,825) | ​ | ​ | 7,175
Pass-through MBS issued by GSEs | ​ | ​ | 279,853 | ​ | ​ | — | ​ | ​ | (37,579) | ​ | ​ | 242,274
Agency CMOs | ​ |  | 216,223 | ​ |  | 16 | ​ |  | (27,021) | ​ |  | 189,218
Total securities held-to-maturity | ​ | $ | 594,639 | ​ | $ | 16 | ​ | $ | (77,725) | ​ | $ | 516,930
​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | December 31, 2022
​ | ​ | ​ | ​ | ​ | Gross | ​ | Gross | ​ | ​ | ​
​ | ​ | Amortized | ​ | Unrealized | ​ | Unrealized | ​ | Fair
(In thousands) |  | Cost |  | Gains |  | Losses |  | Value
Securities available-for-sale: |  | ​ |  |  | ​ |  |  | ​ |  |  | ​ |
Treasury securities | ​ | $ | 246,899 | ​ | $ | — | ​ | $ | (19,643) | ​ | $ | 227,256
Corporate securities | ​ | ​ | 183,791 | ​ |  | 57 | ​ |  | (17,075) | ​ |  | 166,773
Pass-through MBS issued by GSEs | ​ |  | 272,774 | ​ |  | — | ​ |  | (31,534) | ​ |  | 241,240
Agency CMOs | ​ |  | 331,394 | ​ |  | 2 | ​ |  | (50,057) | ​ |  | 281,339
State and municipal obligations | ​ |  | 37,000 | ​ | ​ | — | ​ | ​ | (3,021) | ​ | ​ | 33,979
Total securities available-for-sale | ​ | $ | 1,071,858 | ​ | $ | 59 | ​ | $ | (121,330) | ​ | $ | 950,587
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | December 31, 2022
​ | ​ | ​ | ​ | ​ | Gross | ​ | Gross | ​ | ​ | ​
​ | ​ | Amortized | ​ | Unrecognized | ​ | Unrecognized | ​ | Fair
(In thousands) |  | Cost |  | Gains |  | Losses |  | Value
Securities held-to-maturity: |  | ​ |  |  | ​ |  |  | ​ |  |  | ​ |
Agency notes | ​ | $ | 89,157 | ​ | $ | — | ​ | $ | (14,095) | ​ | $ | 75,062
Corporate securities | ​ | ​ | 9,000 | ​ | ​ | — | ​ | ​ | (553) | ​ | ​ | 8,447
Pass-through MBS issued by GSEs | ​ | ​ | 278,281 | ​ | ​ | — | ​ | ​ | (40,960) | ​ | ​ | 237,321
Agency CMOs | ​ |  | 209,360 | ​ |  | — | ​ |  | (24,431) | ​ |  | 184,929
Total securities held-to-maturity | ​ | $ | 585,798 | ​ | $ | — | ​ | $ | (80,039) | ​ | $ | 505,759
Amortized cost and fair value of securities are shown by contractual maturity | ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | December 31, 2023
​ | ​ | Amortized | ​ | Fair
(In thousands) | ​ | Cost | ​ | Value
Available-for-sale | ​ | ​ | ​ | ​ | ​ | ​
Within one year | ​ | $ | 88,498 | ​ | $ | 86,233
One to five years | ​ | ​ | 198,552 | ​ | ​ | 186,041
Five to ten years | ​ | ​ | 172,546 | ​ | ​ | 149,266
Beyond ten years | ​ | ​ | — | ​ | ​ | —
Pass-through MBS issued by GSEs and agency CMO | ​ | ​ | 536,113 | ​ | ​ | 464,700
Total | ​ | $ | 995,709 | ​ | $ | 886,240
​ | ​ | ​ | ​ | ​ | ​ | ​
Held-to-maturity | ​ | ​ | ​ | ​ | ​ | ​
Within one year | ​ | $ | — | ​ | $ | —
One to five years | ​ | ​ | 19,783 | ​ | ​ | 18,397
Five to ten years | ​ | ​ | 78,780 | ​ | ​ | 67,041
Beyond ten years | ​ | ​ | — | ​ | ​ | —
Pass-through MBS issued by GSEs and agency CMO | ​ | ​ | 496,076 | ​ | ​ | 431,492
Total | ​ | $ | 594,639 | ​ | $ | 516,930
Summary of sale of available-for-sale securities | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Year Ended December 31,
(In thousands) | ​ | 2023 |  | 2022 |  | 2021
Proceeds | ​ | $ | 77,804 | ​ | $ | — | ​ | $ | 138,077
Gross gains | ​ | ​ | 130 | ​ | ​ | — | ​ | ​ | 1,327
Tax expense on gains | ​ | ​ | 39 | ​ | ​ | — | ​ | ​ | 421
Gross losses | ​ | ​ | 1,577 | ​ | ​ | — | ​ | ​ | 120
Tax benefit on losses | ​ | ​ | 467 | ​ | ​ | — | ​ | ​ | 38
Sales of Marketable Equity Securities | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Year Ended December 31,
(In thousands) | ​ | 2023 |  | 2022 |  | 2021
Proceeds: | ​ | ​ |  |  | ​ |  |  | ​ |
Marketable equity securities | ​ | $ | — | ​ | $ | — | ​ | $ | 6,101
Schedule of gross unrealized losses and fair value of investment securities | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | December 31, 2023
​ | ​ | Less than 12 | ​ | 12 Consecutive | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Consecutive Months | ​ | Months or Longer | ​ | Total
​ | ​ | Fair | ​ | Unrealized | ​ | Fair | ​ | Unrealized | ​ | Fair | ​ | Unrealized
(In thousands) |  | Value |  | Losses |  | Value |  | Losses |  | Value |  | Losses
Securities available-for-sale: |  | ​ |  |  | ​ |  |  | ​ |  |  | ​ |  |  | ​ |  |  | ​ |
Agency notes | ​ | $ | — | ​ | $ | — | ​ | $ | 9,371 | ​ | $ | 629 | ​ | $ | 9,371 | ​ | $ | 629
Treasury securities | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 234,190 | ​ | ​ | 11,687 | ​ | ​ | 234,190 | ​ | ​ | 11,687
Corporate securities | ​ | ​ | 20,935 | ​ | ​ | 917 | ​ | ​ | 130,235 | ​ | ​ | 22,891 | ​ | ​ | 151,170 | ​ | ​ | 23,808
Pass-through MBS issued by GSEs | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 203,469 | ​ | ​ | 24,978 | ​ | ​ | 203,469 | ​ | ​ | 24,978
Agency CMOs | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 251,900 | ​ | ​ | 46,491 | ​ | ​ | 251,900 | ​ | ​ | 46,491
State and municipal obligations | ​ |  | 1,796 | ​ |  | 54 | ​ |  | 21,513 | ​ |  | 1,878 | ​ | ​ | 23,309 | ​ | ​ | 1,932
​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | December 31, 2022
​ | ​ | Less than 12 | ​ | 12 Consecutive | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Consecutive Months | ​ | Months or Longer | ​ | Total
​ | ​ | Fair | ​ | Unrealized | ​ | Fair | ​ | Unrealized | ​ | Fair | ​ | Unrealized
(In thousands) |  | Value |  | Losses |  | Value |  | Losses |  | Value |  | Losses
Securities available-for-sale: |  | ​ |  |  | ​ |  |  | ​ |  |  | ​ |  |  | ​ |  |  | ​ |
Treasury securities | ​ | $ | — | ​ | $ | — | ​ | $ | 227,256 | ​ | $ | 19,643 | ​ | $ | 227,256 | ​ | $ | 19,643
Corporate securities | ​ | ​ | 110,707 | ​ | ​ | 8,494 | ​ | ​ | 50,116 | ​ | ​ | 8,581 | ​ | ​ | 160,823 | ​ | ​ | 17,075
Pass-through MBS issued by GSEs | ​ | ​ | 50,813 | ​ | ​ | 2,010 | ​ | ​ | 190,427 | ​ | ​ | 29,524 | ​ | ​ | 241,240 | ​ | ​ | 31,534
Agency CMOs | ​ | ​ | 55,924 | ​ | ​ | 3,454 | ​ | ​ | 220,413 | ​ | ​ | 46,603 | ​ | ​ | 276,337 | ​ | ​ | 50,057
State and municipal obligations | ​ | ​ | 10,848 | ​ |  | 174 | ​ |  | 22,681 | ​ |  | 2,847 | ​ | ​ | 33,529 | ​ | ​ | 3,021

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