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BENEFIT PLANS, Funded Status and Amounts Recognized in Balance Sheets and AOCI (Details) - USD ($) $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2009 | Jun. 01, 2018
Amounts recognized in accumulated other comprehensive loss/(income) ("AOCI") [Abstract] |  |  |  |  |
AOCI at year end | $ 34,882 | $ 32,837 | $ 21,633 |  |
Accumulated other comprehensive income (loss), negative postretirement medical plan amendment, arising during period, net of tax |  |  |  | $ 3,500 |
Stock Balance Plan [Member] | Nonemployee Directors [Member] |  |  |  |  |
Pension Plan [Abstract] |  |  |  |  |
Defined Benefit Plan, Funding Status [Extensible List] | us-gaap:UnfundedPlanMember |  |  |  |
Change in benefit obligation [Roll Forward] |  |  |  |  |
Benefit obligation at the beginning of year | $ 100 |  |  |  |
Benefit obligation at end of year | 100 | 100 |  |  |
Pension Benefits [Member] |  |  |  |  |
Change in benefit obligation [Roll Forward] |  |  |  |  |
Benefit obligation at the beginning of year | 144,211 | 147,450 |  |  |
Service cost | 5,081 | 4,561 | 4,181 |  |
Interest cost | 6,264 | 5,676 | 5,717 |  |
Plan amendment / acquisition | 0 | 883 |  |  |
Participant contributions | 0 | 0 |  |  |
Deferred actuarial (gain)/loss | 16,292 | (4,177) |  |  |
Benefits paid | (9,764) | (10,182) |  |  |
Benefit obligation at end of year | 162,084 | 144,211 | 147,450 |  |
Change in plan assets [Roll Forward] |  |  |  |  |
Fair value of plan assets at beginning of year | 203,672 | 217,107 |  |  |
Actual return of plan assets | 25,522 | (3,858) |  |  |
Participant contributions | 0 | 0 |  |  |
Employer contributions | 7,893 | 605 |  |  |
Plan acquisition | 0 | 0 |  |  |
Benefits paid | (9,764) | (10,182) |  |  |
Fair value of plan assets at end of year | 227,323 | 203,672 | 217,107 |  |
Over/(Under) funded status at year end | 65,239 | 59,461 |  |  |
Amounts recognized in the consolidated statement of condition [Abstract] |  |  |  |  |
Other assets | 81,930 | 72,659 |  |  |
Other liabilities | (16,691) | (13,198) |  |  |
Amounts recognized in accumulated other comprehensive loss/(income) ("AOCI") [Abstract] |  |  |  |  |
Net loss | 41,924 | 39,410 |  |  |
Net prior service cost (credit) | 4,875 | 4,939 |  |  |
Pre-tax AOCI | 46,799 | 44,349 |  |  |
Taxes | (11,448) | (10,870) |  |  |
AOCI at year end | 35,351 | 33,479 |  |  |
Pension Benefits [Member] | Nonqualified Plan [Member] | us-gaap_UnfundedPlanMember |  |  |  |  |
Change in plan assets [Roll Forward] |  |  |  |  |
Employer contributions | 7,300 |  |  |  |
Pension Benefits [Member] | Restoration Plan [Member] | Nonqualified Plan [Member] | us-gaap_UnfundedPlanMember |  |  |  |  |
Amounts recognized in accumulated other comprehensive loss/(income) ("AOCI") [Abstract] |  |  |  |  |
Initial projected benefit obligation | 300 | 100 |  |  | $ 800
Post-retirement Benefits [Member] |  |  |  |  |
Change in benefit obligation [Roll Forward] |  |  |  |  |
Benefit obligation at the beginning of year | 1,657 | 1,785 |  |  |
Service cost | 0 | 0 | 0 |  |
Interest cost | 70 | 69 | 76 |  |
Plan amendment / acquisition | 0 | 0 |  |  |
Participant contributions | 35 | 479 |  |  |
Deferred actuarial (gain)/loss | 87 | 191 |  |  |
Benefits paid | (172) | (867) |  |  |
Benefit obligation at end of year | 1,677 | 1,657 | 1,785 |  |
Change in plan assets [Roll Forward] |  |  |  |  |
Fair value of plan assets at beginning of year | 0 | 0 |  |  |
Actual return of plan assets | 0 | 0 |  |  |
Participant contributions | 35 | 479 |  |  |
Employer contributions | 137 | 388 |  |  |
Plan acquisition | 0 | 0 |  |  |
Benefits paid | (172) | (867) |  |  |
Fair value of plan assets at end of year | 0 | 0 | $ 0 |  |
Over/(Under) funded status at year end | (1,677) | (1,657) |  |  |
Amounts recognized in the consolidated statement of condition [Abstract] |  |  |  |  |
Other assets | 0 | 0 |  |  |
Other liabilities | (1,677) | (1,657) |  |  |
Amounts recognized in accumulated other comprehensive loss/(income) ("AOCI") [Abstract] |  |  |  |  |
Net loss | 641 | 592 |  |  |
Net prior service cost (credit) | (1,265) | (1,444) |  |  |
Pre-tax AOCI | (624) | (852) |  |  |
Taxes | 155 | 210 |  |  |
AOCI at year end | $ (469) | (642) |  |  |
Supplemental Pension Plans [Member] | Key Executives [Member] |  |  |  |  |
Pension Plan [Abstract] |  |  |  |  |
Defined Benefit Plan, Funding Status [Extensible List] | us-gaap:UnfundedPlanMember |  |  |  |
Change in benefit obligation [Roll Forward] |  |  |  |  |
Benefit obligation at the beginning of year | $ 13,200 |  |  |  |
Benefit obligation at end of year | 16,400 | 13,200 |  |  |
Amounts recognized in accumulated other comprehensive loss/(income) ("AOCI") [Abstract] |  |  |  |  |
Benefit obligation for defined benefit pension plan prior to plan revaluation | $ 145,400 | $ 131,000 |  |  |

X
- Definition The tax on net gain (loss) on prior service cost (credit), and transition assets (obligations), as well as minimum pension liability if still remaining, included in accumulated other comprehensive income associated with a defined benefit pension or other postretirement plan(s) because they have yet to be recognized as components of net periodic benefit cost. + References No definition available. + Details
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- Definition The benefit obligation is the projected benefit obligation, which is the actuarial present value as of a date of all benefits attributed by the pension benefit formula to employee service rendered prior to plan revaluation. + References No definition available. + Details
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