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RETIREMENT AND POSTRETIREMENT PLANS (Tables) | 12 Months Ended
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Dec. 31, 2021
Employee Retirement Plan |
Defined Benefit Plan Disclosure [Line Items] |
Schedule of funded status of defined benefit plan | ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Year Ended December 31,
(In thousands) |  | 2021 |  | 2020
Reconciliation of projected benefit obligation: | ​ |  |  | ​ |  |
Projected benefit obligation at beginning of year | ​ | $ | 26,891 | ​ | $ | 25,405
Interest cost | ​ |  | 562 | ​ |  | 732
Actuarial (gain) loss | ​ |  | (903) | ​ |  | 2,204
Benefit payments | ​ |  | (1,589) | ​ |  | (1,450)
Projected benefit obligation at end of year | ​ |  | 24,961 | ​ |  | 26,891
​ | ​ |  |  | ​ |  |
Plan assets at fair value (investments in trust funds managed by trustee) | ​ |  |  | ​ |  |
Balance at beginning of year | ​ |  | 27,142 | ​ |  | 25,202
Return on plan assets | ​ |  | 3,140 | ​ |  | 3,390
Benefit payments | ​ |  | (1,589) | ​ |  | (1,450)
Balance at end of year | ​ |  | 28,693 | ​ |  | 27,142
Funded status at end of year | ​ | $ | 3,732 | ​ | $ | 251
Schedule of net periodic cost of defined benefit plan | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Year Ended December 31,
(In thousands) | ​ | 2021 |  | 2020 |  | 2019
Interest cost | ​ | $ | 562 | ​ | $ | 732 | ​ | $ | 901
Expected return on plan assets | ​ |  | (1,846) | ​ |  | (1,713) | ​ |  | (1,528)
Amortization of unrealized loss | ​ |  | 824 | ​ |  | 914 | ​ |  | 913
Net periodic benefit (credit) cost | ​ | $ | (460) | ​ | $ | (67) | ​ | $ | 286
Schedule of change in accumulated other comprehensive loss | ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Year Ended December 31,
(In thousands) |  | 2021 |  | 2020
Balance at beginning of period | ​ | $ | (7,119) | ​ | $ | (7,506)
Amortization of unrealized loss | ​ |  | 825 | ​ |  | 914
Gain (loss) recognized during the year | ​ |  | 2,197 | ​ |  | (527)
Balance at the end of the period | ​ | $ | (4,097) | ​ | $ | (7,119)
Period end component of accumulated other comprehensive loss, net of tax | ​ | $ | 2,808 | ​ | $ | 4,858
Schedule of major assumptions utilized to determine the net periodic cost of the Employee Retirement Plan benefit obligations | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | At or for the Year Ended December 31, |
​ |  | 2021 |  | 2020 |  | 2019 |
Discount rate used for net periodic benefit cost |  | 2.55 | % | 2.97 | % | 4.04 | %
Discount rate used to determine benefit obligation at period end |  | 2.55 |  | 2.15 |  | 2.97 | ​
Expected long-term return on plan assets used for net periodic benefit cost |  | 7.00 |  | 7.00 |  | 7.00 | ​
Expected long-term return on plan assets used to determine benefit obligation at period end |  | 7.00 |  | 7.00 |  | 7.00 | ​
Summary of plan asset allocation by asset category | ​
​ | ​ | ​ | ​ | ​ | ​
​ | ​ | December 31, |
​ |  | 2021 |  | 2020 |
Asset category |  |  |  |  | ​
Equity securities |  | 54 | % | 67 | %
Debt securities (bond mutual funds) |  | 42 |  | 30 | ​
Cash equivalents |  | 4 |  | 3 | ​
Total |  | 100 | % | 100 | %
Summary of fair values of the plan assets | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | December 31, 2021
​ | ​ | Fair Value Measurements Using:
​ | ​ | Quoted | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Prices in | ​ | Significant | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Active Markets for | ​ | Other | ​ | Significant | ​ | ​ | ​
​ | ​ | Identical | ​ | Observable | ​ | Unobservable | ​ | ​ | ​
(In thousands) |  | Assets (Level 1) |  | Inputs (Level 2) |  | Inputs (Level 3) |  | Total
Description: | ​ |  | ​ | ​ | ​ | ​ | ​ |  | ​ | ​ |  | ​
Cash and cash equivalents | ​ | $ | — | ​ | $ | 1,001 | ​ | $ | — | ​ | $ | 1,001
Equities: | ​ |  | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
U.S. large cap | ​ |  | 8,579 | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 8,579
U.S. mid cap/small cap | ​ |  | 2,896 | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 2,896
International | ​ |  | 3,560 | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 3,560
Equities blend | ​ |  | 479 | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 479
Fixed income securities: | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Corporate | ​ | ​ | — | ​ | ​ | 1,288 | ​ | ​ | — | ​ | ​ | 1,288
Government | ​ | ​ | 1,406 | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 1,406
Mortgage-backed | ​ |  | — | ​ | ​ | 1,858 | ​ | ​ | — | ​ | ​ | 1,858
High yield bonds and bond funds | ​ |  | — | ​ | ​ | 7,626 | ​ | ​ | — | ​ | ​ | 7,626
Total Plan Assets | ​ | $ | 16,920 | ​ | $ | 11,773 | ​ | $ | — | ​ | $ | 28,693
​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | December 31, 2020
​ | ​ | Fair Value Measurements Using:
​ | ​ | Quoted | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Prices in | ​ | Significant | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Active Markets for | ​ | Other | ​ | Significant | ​ | ​ | ​
​ | ​ | Identical | ​ | Observable | ​ | Unobservable | ​ | ​ | ​
(In thousands) |  | Assets (Level 1) |  | Inputs (Level 2) |  | Inputs (Level 3) |  | Total
Description: | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Cash and cash equivalents | ​ | $ | 720 | ​ | $ | — | ​ | $ | — | ​ | $ | 720
Mutual Funds (all registered and publicly traded) : | ​ |  | ​ | ​ |  | ​ | ​ |  | ​ | ​ |  | ​
U.S. Large Cap | ​ | ​ | 3,336 | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 3,336
U.S. Mid Cap | ​ |  | 1,571 | ​ |  | — | ​ |  | — | ​ |  | 1,571
U.S. Small Cap | ​ |  | 618 | ​ |  | — | ​ |  | — | ​ |  | 618
International Equity | ​ |  | 4,678 | ​ |  | — | ​ |  | — | ​ |  | 4,678
Fixed income | ​ |  | 8,300 | ​ |  | — | ​ |  | — | ​ |  | 8,300
Common collective investment funds: | ​ |  |  | ​ |  |  | ​ |  |  | ​ |  |
U.S. Large Cap | ​ |  | — | ​ |  | 5,564 | ​ |  | — | ​ |  | 5,564
U.S. Mid Cap | ​ |  | — | ​ |  | 742 | ​ |  | — | ​ |  | 742
U.S. Small Cap | ​ |  | — | ​ |  | 1,613 | ​ |  | — | ​ |  | 1,613
Total Plan Assets | ​ | $ | 19,223 | ​ | $ | 7,919 | ​ | $ | — | ​ | $ | 27,142
Schedule of expected benefit payments maturities | ​
​ | ​ | ​ | ​
Year Ended December 31, | ​ | Amount
2022 | ​ | $ | 1,501
2023 | ​ |  | 1,490
2024 | ​ |  | 1,477
2025 | ​ |  | 1,412
2026 | ​ |  | 1,368
2027 to 2031 | ​ |  | 6,503
Retirement Plans [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Schedule of funded status of defined benefit plan | ​
​ | ​ | ​ | ​
​ | ​ | Year Ended December 31,
(In thousands) |  | 2021
Reconciliation of projected benefit obligation: | ​ |  |
Projected benefit obligation at beginning of year | ​ | $ | —
Acquired in the Merger | ​ | ​ | 33,897
Service cost | ​ |  | 893
Interest cost | ​ |  | 609
Actuarial gain | ​ | ​ | (304)
Benefit payments | ​ |  | (600)
Projected benefit obligation at end of year | ​ |  | 34,495
​ | ​ |  |
Plan assets at fair value (investments in trust funds managed by trustee) | ​ |  |
Balance at beginning of year | ​ |  | —
Acquired in the Merger | ​ | ​ | 43,685
Return on plan assets | ​ |  | 4,772
Benefit payments | ​ |  | (600)
Balance at end of year | ​ |  | 47,857
Funded status at end of year | ​ | $ | 13,362
Schedule of net periodic cost of defined benefit plan | ​
​ | ​ | ​ | ​
​ | ​ | Year Ended December 31,
(In thousands) | ​ | 2021
Service cost | ​ | $ | 893
Interest cost | ​ | ​ | 609
Expected return on plan assets | ​ |  | (2,883)
Net periodic benefit credit | ​ | $ | (1,381)
Schedule of change in accumulated other comprehensive loss | ​
​ | ​ | ​ | ​
​ | ​ | Year Ended December 31,
(In thousands) |  | 2021
Balance at beginning of period | ​ | $ | —
Gain recognized during the year | ​ |  | 2,193
Balance at the end of the period | ​ | $ | 2,193
Period end component of accumulated other comprehensive income, net of tax | ​ | $ | (1,503)
Schedule of major assumptions utilized to determine the net periodic cost of the Employee Retirement Plan benefit obligations | ​
​ | ​ | ​ | ​
​ | ​ | At or for the Year Ended December 31, | ​
​ |  | 2021 |
Discount rate used for net periodic benefit cost |  | 2.69 | %
Discount rate used to determine benefit obligation at period end |  | 2.69 |
Expected long-term return on plan assets used for net periodic benefit cost |  | 7.25 |
Expected long-term return on plan assets used to determine benefit obligation at period end |  | 7.25 |
Summary of plan asset allocation by asset category | ​
​ | ​ | ​ | ​
​ | ​ | December 31, | ​
​ |  | 2021 |
Asset category |  |  |
Equity securities |  | 60 | %
Debt securities (bond mutual funds) |  | 37 |
Cash equivalents |  | 3 |
Total |  | 100 | %
Summary of fair values of the plan assets | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | December 31, 2021
​ | ​ | Fair Value Measurements Using:
​ | ​ | Quoted | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Prices in | ​ | Significant | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Active Markets for | ​ | Other | ​ | Significant | ​ | ​ | ​
​ | ​ | Identical | ​ | Observable | ​ | Unobservable | ​ | ​ | ​
(In thousands) |  | Assets (Level 1) |  | Inputs (Level 2) |  | Inputs (Level 3) |  | Total
Description: | ​ |  | ​ | ​ | ​ | ​ | ​ |  | ​ | ​ |  | ​
Cash and cash equivalents | ​ | $ | — | ​ | $ | 1,581 | ​ | $ | — | ​ | $ | 1,581
Equities: | ​ |  | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
U.S. large cap | ​ |  | 13,623 | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 13,623
U.S. mid cap/small cap | ​ |  | 5,669 | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 5,669
International | ​ |  | 8,332 | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 8,332
Equities blend | ​ |  | 900 | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 900
Fixed income securities: | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Corporate | ​ | ​ | — | ​ | ​ | 1,696 | ​ | ​ | — | ​ | ​ | 1,696
Government | ​ | ​ | 1,700 | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 1,700
Mortgage-backed | ​ |  | — | ​ | ​ | 2,549 | ​ | ​ | — | ​ | ​ | 2,549
High yield bonds and bond funds | ​ |  | — | ​ | ​ | 11,807 | ​ | ​ | — | ​ | ​ | 11,807
Total Plan Assets | ​ | $ | 30,224 | ​ | $ | 17,633 | ​ | $ | — | ​ | $ | 47,857
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Schedule of expected benefit payments maturities | ​
​ | ​ | ​ | ​
Year Ended December 31, | ​ | Amount
2022 | ​ | $ | 1,119
2023 | ​ |  | 1,264
2024 | ​ |  | 1,274
2025 | ​ |  | 1,360
2026 | ​ |  | 1,563
2027 to 2031 | ​ |  | 9,153
BMP and Outside Director Retirement Plan |
Defined Benefit Plan Disclosure [Line Items] |
Schedule of funded status of defined benefit plan | ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Year Ended December 31,
(In thousands) |  | 2021 |  | 2020
Reconciliation of projected benefit obligation: | ​ |  |  | ​ |  |
Projected benefit obligation at beginning of year | ​ | $ | 9,328 | ​ | $ | 9,360
Interest cost | ​ |  | 12 | ​ |  | 234
Benefit payments | ​ |  | (9,063) | ​ |  | (771)
Actuarial (gain) loss | ​ |  | (277) | ​ |  | 505
Projected benefit obligation at end of year | ​ |  | — | ​ |  | 9,328
Plan assets at fair value: | ​ |  |  | ​ |  |
Balance at beginning of year | ​ |  | — | ​ |  | —
Contributions | ​ |  | 9,063 | ​ |  | 771
Benefit payments | ​ |  | (9,063) | ​ |  | (771)
Balance at end of period | ​ |  | — | ​ |  | —
Funded status at end of year | ​ | $ | — | ​ | $ | (9,328)
Schedule of net periodic cost of defined benefit plan | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Year Ended December 31,
(In thousands) |  | 2021 |  | 2020 |  | 2019
Interest cost | ​ | $ | 12 | ​ | $ | 234 | ​ | $ | 351
Curtailment loss | ​ | ​ | 1,543 | ​ | ​ | — | ​ | ​ | —
Amortization of unrealized loss | ​ |  | — | ​ |  | 179 | ​ |  | 59
Net periodic benefit cost | ​ | $ | 1,555 | ​ | $ | 413 | ​ | $ | 410
Schedule of change in accumulated other comprehensive loss | ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Year Ended December 31,
(In thousands) |  | 2021 |  | 2020
Balance at beginning of year | ​ | $ | (1,820) | ​ | $ | (1,494)
Amortization of unrealized loss | ​ |  | — | ​ |  | 179
Gain (loss) recognized during the year | ​ |  | 277 | ​ |  | (505)
Curtailment credit | ​ | ​ | 1,543 | ​ | ​ | —
Balance at the end of year | ​ | $ | — | ​ | $ | (1,820)
Period end component of accumulated other comprehensive loss, net of tax | ​ | $ | — | ​ | $ | 1,228
Schedule of major assumptions utilized to determine the net periodic cost of the Employee Retirement Plan benefit obligations | ​
​ | ​ | ​ | ​ | ​ | ​
​ | ​ | At or For the Year Ended December 31, |
​ |  | 2020 |  | 2019 |
Discount rate used for net periodic benefit cost – BMP |  | 2.60 | % | 3.80 | %
Discount rate used for net periodic benefit cost – Director Retirement Plan |  | 2.68 |  | 3.84 | ​
Discount rate used to determine BMP benefit obligation at year end |  | 1.55 |  | 2.60 | ​
Discount rate used to determine Director Retirement Plan benefit obligation at year end |  | 1.69 |  | 2.68 | ​
​
POSTRETIREMENT PLANS |
Defined Benefit Plan Disclosure [Line Items] |
Schedule of funded status of defined benefit plan | ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Year Ended December 31,
(In thousands) |  | ​ | 2021 |  | ​ | 2020
Reconciliation of projected benefit obligation: | ​ |  |  | ​ |  |
Projected benefit obligation at beginning of year | ​ | $ | 13 | ​ | $ | 1,608
Interest cost | ​ |  | — | ​ |  | 42
Actuarial loss | ​ |  | — | ​ |  | 105
Curtailment gain | ​ | ​ | — | ​ | ​ | (1,577)
Benefit payments | ​ |  | (13) | ​ |  | (165)
Projected benefit obligation at end of year | ​ |  | — | ​ |  | 13
Plan assets at fair value: | ​ |  |  | ​ |  |
Balance at beginning of year | ​ |  | — | ​ |  | —
Contributions | ​ |  | 13 | ​ |  | 165
Benefit payments | ​ |  | (13) | ​ |  | (165)
Balance at end of period | ​ |  | — | ​ |  | —
Funded status at end of year | ​ | $ | — | ​ | $ | (13)
Schedule of net periodic cost of defined benefit plan | ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Year Ended December 31,
(In thousands) |  | 2020 |  | 2019
Interest cost | ​ | $ | 42 | ​ | $ | 56
Curtailment gain | ​ | ​ | 1,651 | ​ | ​ | —
Amortization of unrealized loss | ​ |  | (9) | ​ |  | (20)
Net periodic benefit cost | ​ | $ | 1,684 | ​ | $ | 36
Schedule of change in accumulated other comprehensive loss | ​
​ | ​ | ​ | ​
​ | ​ | ​ | Year Ended December 31,
(In thousands) |  | 2020
Balance at beginning of period | ​ | $ | 188
Amortization of unrealized loss | ​ |  | (9)
Recognition of prior service cost | ​ | ​ | (74)
Loss recognized during the year | ​ |  | (105)
Balance at the end of the period | ​ | $ | —
Period end component of accumulated other comprehensive loss, net of tax | ​ | $ | —
Schedule of major assumptions utilized to determine the net periodic cost of the Employee Retirement Plan benefit obligations | ​
​ | ​ | ​ | ​ | ​ | ​
​ | ​ | At or For the Year Ended December 31, |
​ |  | 2020 |  | 2019 |
Discount rate used for net periodic benefit cost |  | 2.69 | % | 3.82 | %
Discount rate used to determine benefit obligation at period end |  | 0.29 |  | 2.69 | ​

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