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INVESTMENT AND MORTGAGE-BACKED SECURITIES (Tables) | 9 Months Ended
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Sep. 30, 2021
INVESTMENT AND MORTGAGE-BACKED SECURITIES |
Major Categories of Securities Owned by Entity | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | September 30, 2021
​ | ​ | ​ | ​ | ​ | Gross | ​ | Gross | ​ | ​ | ​
​ | ​ | Amortized | ​ | Unrealized | ​ | Unrealized | ​ | Fair
(In thousands) |  | Cost |  | Gains |  | Losses |  | Value
Securities available-for-sale: |  | ​ |  |  | ​ |  |  | ​ |  |  | ​ |
Agency notes | ​ | $ | 82,475 | ​ | $ | — | ​ | $ | (1,457) | ​ | $ | 81,018
Treasury securities | ​ | ​ | 248,173 | ​ | ​ | 5 | ​ | ​ | (482) | ​ | ​ | 247,696
Corporate securities | ​ |  | 122,476 | ​ |  | 4,758 | ​ |  | (401) | ​ |  | 126,833
Pass-through MBS issued by GSEs | ​ |  | 622,225 | ​ |  | 6,005 | ​ |  | (6,273) | ​ |  | 621,957
Agency Collateralized Mortgage Obligations ("CMOs") | ​ |  | 590,385 | ​ |  | 5,159 | ​ |  | (5,118) | ​ |  | 590,426
State and municipal obligations | ​ | ​ | 41,158 | ​ | ​ | 153 | ​ | ​ | (178) | ​ | ​ | 41,133
Total securities available-for-sale | ​ | $ | 1,706,892 | ​ | $ | 16,080 | ​ | $ | (13,909) | ​ | $ | 1,709,063
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | September 30, 2021
​ | ​ | ​ | ​ | ​ | Gross | ​ | Gross | ​ | ​ | ​
​ | ​ | Amortized | ​ | Unrecognized | ​ | Unrecognized | ​ | Fair
(In thousands) |  | Cost |  | Gains |  | Losses |  | Value
Securities held-to-maturity: |  | ​ |  |  | ​ |  |  | ​ |  |  | ​ |
Pass-through MBS issued by GSEs | ​ | $ | 25,325 | ​ | $ | — | ​ | $ | — | ​ | $ | 25,325
Agency Collateralized Mortgage Obligations ("CMOs") | ​ |  | 14,978 | ​ |  | — | ​ |  | — | ​ |  | 14,978
Total securities held-to-maturity | ​ | $ | 40,303 | ​ | $ | — | ​ | $ | — | ​ | $ | 40,303
​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | December 31, 2020
​ | ​ | ​ | ​ | ​ | Gross | ​ | Gross | ​ | ​ | ​
​ | ​ | Amortized | ​ | Unrealized | ​ | Unrealized | ​ | Fair
(In thousands) |  | Cost |  | Gains |  | Losses |  | Value
Securities available-for-sale: |  | ​ |  |  | ​ |  |  | ​ |  |  | ​ |
Agency notes | ​ | $ | 47,500 | ​ | $ | 12 | ​ | $ | (91) | ​ | $ | 47,421
Corporate securities | ​ |  | 62,021 | ​ |  | 2,440 | ​ |  | — | ​ |  | 64,461
Pass-through MBS issued by GSEs | ​ |  | 135,842 | ​ |  | 7,672 | ​ |  | (31) | ​ |  | 143,483
Agency CMOs | ​ |  | 274,898 | ​ |  | 8,674 | ​ |  | (76) | ​ |  | 283,496
Total securities available-for-sale | ​ | $ | 520,261 | ​ | $ | 18,798 | ​ | $ | (198) | ​ | $ | 538,861
Schedule of amortized cost and fair value of debt securities | ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | ​ |
​ | ​ | September 30, 2021
​ | ​ | Amortized | ​ | Fair
(In thousands) | ​ | Cost | ​ | Value
Available-for-sale | ​ | ​ | ​ | ​ | ​ | ​
Within one year | ​ | $ | 1,346 | ​ | $ | 1,351
One to five years | ​ | ​ | 270,069 | ​ | ​ | 269,665
Five to ten years | ​ | ​ | 209,938 | ​ | ​ | 212,881
Beyond ten years | ​ | ​ | 12,929 | ​ | ​ | 12,783
Pass-through MBS issued by GSEs and agency CMO | ​ | ​ | 1,212,610 | ​ | ​ | 1,212,383
Total | ​ | $ | 1,706,892 | ​ | $ | 1,709,063
​ | ​ | ​ | ​ | ​ | ​ | ​
Held-to-maturity | ​ | ​ | ​ | ​ | ​ | ​
Pass-through MBS issued by GSEs and agency CMO | ​ | $ | 40,303 | ​ | $ | 40,303
Total | ​ | $ | 40,303 | ​ | $ | 40,303
Summary of Sale of Available-for-sale Securities | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Three Months Ended | ​ | Nine Months Ended
​ | ​ | September 30, | ​ | September 30,
(In thousands) |  | 2021 |  | 2020 | ​ | 2021 |  | 2020
Agency Notes: | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Proceeds | ​ | $ | — | ​ | $ | — | ​ | $ | — | ​ | $ | 273
Gross gains | ​ | ​ | — | ​ | ​ | — | ​ | ​ | — | ​ | ​ | —
Tax expense on gain | ​ | ​ | — | ​ | ​ | — | ​ | ​ | — | ​ | ​ | —
Gross losses | ​ | ​ | — | ​ | ​ | — | ​ | ​ | — | ​ | ​ | —
Tax benefit on loss | ​ | ​ | — | ​ | ​ | — | ​ | ​ | — | ​ | ​ | —
Corporate Securities: | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Proceeds | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 50,273 | ​ | ​ | 25,403
Gross gains | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 729 | ​ | ​ | 1,344
Tax expense on gain | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 232 | ​ | ​ | 423
Gross losses | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 41 | ​ | ​ | —
Tax benefit on loss | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 13 | ​ | ​ | —
Pass through MBS issued by GSEs: |  | ​ | ​ |  | ​ |  | ​ | ​ |  |  | ​ |
Proceeds | ​ | ​ | — | ​ | ​ | 5,987 | ​ | ​ | 26,823 | ​ | ​ | 39,182
Gross gains | ​ |  | — | ​ |  | 215 | ​ |  | 187 | ​ |  | 2,005
Tax expense on gain | ​ |  | — | ​ |  | 67 | ​ |  | 59 | ​ |  | 630
Gross losses | ​ |  | — | ​ |  | — | ​ |  | 35 | ​ |  | —
Tax benefit on loss | ​ |  | — | ​ |  | — | ​ |  | 11 | ​ |  | —
Agency CMOs: | ​ |  |  | ​ |  | ​ | ​ |  |  | ​ |  |
Proceeds | ​ |  | — | ​ |  | — | ​ |  | 41,324 | ​ |  | 4,199
Gross gains | ​ |  | — | ​ |  | — | ​ |  | 268 | ​ |  | 8
Tax expense on gain | ​ |  | — | ​ |  | — | ​ |  | 85 | ​ |  | 3
Gross losses | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 44 | ​ | ​ | —
Tax benefit on loss | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 14 | ​ | ​ | —
State and municipal obligations: | ​ |  |  | ​ |  |  | ​ |  |  | ​ |  |
Proceeds | ​ |  | — | ​ |  | — | ​ |  | 19,657 | ​ |  | —
Gross gains | ​ |  | — | ​ |  | — | ​ |  | 143 | ​ |  | —
Tax expense on gain | ​ |  | — | ​ |  | — | ​ |  | 45 | ​ |  | —
Gross losses | ​ | ​ | — | ​ | ​ | — | ​ | ​ | — | ​ | ​ | —
Tax benefit on loss | ​ | ​ | — | ​ | ​ | — | ​ | ​ | — | ​ | ​ | —
Sales of Marketable Equity Securities | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Three Months Ended | ​ | Nine Months Ended
​ | ​ | September 30, | ​ | September 30,
(In thousands) |  | 2021 |  | 2020 | ​ | 2021 |  | 2020
Proceeds: |  | ​ |  |  | ​ |  | ​ | ​ |  |  | ​ |
Marketable equity securities | ​ | $ | — | ​ | $ | 137 | ​ | $ | — | ​ | $ | 410
Gross Unrealized Losses and Fair Value of Investment Securities by Investment Category and Length of Time in a Continuous Unrealized Loss Position | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | September 30, 2021
​ | ​ | 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 | ​ | $ | 81,018 | ​ | $ | 1,457 | ​ | $ | — | ​ | $ | — | ​ | $ | 81,018 | ​ | $ | 1,457
Treasury securities | ​ | ​ | 231,984 | ​ | ​ | 482 | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 231,984 | ​ | ​ | 482
Corporate securities | ​ | ​ | 17,863 | ​ | ​ | 401 | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 17,863 | ​ | ​ | 401
Pass-through MBS issued by GSEs | ​ | ​ | 446,864 | ​ | ​ | 6,273 | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 446,864 | ​ | ​ | 6,273
Agency CMOs | ​ | ​ | 347,726 | ​ | ​ | 5,118 | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 347,726 | ​ | ​ | 5,118
State and municipal obligations | ​ |  | 16,412 | ​ |  | 178 | ​ |  | — | ​ |  | — | ​ |  | 16,412 | ​ |  | 178
​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | December 31, 2020
​ | ​ | 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 | ​ | $ | 22,409 | ​ | $ | 91 | ​ | $ | — | ​ | $ | — | ​ | $ | 22,409 | ​ | $ | 91
Pass-through MBS issued by GSEs | ​ |  | 5,007 | ​ |  | 31 | ​ |  | — | ​ |  | — | ​ |  | 5,007 | ​ |  | 31
Agency CMOs | ​ |  | 6,563 | ​ |  | 30 | ​ |  | 4,954 | ​ |  | 46 | ​ |  | 11,517 | ​ |  | 76

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