| OTHER COMPREHENSIVE INCOME (LOSS) (Tables) | 12 Months Ended | 
|---|---|
| Dec. 31, 2020 | |
| Equity [Abstract] | |
| Schedule of other comprehensive income loss | Before  Tax  Net of  Tax  (Expense)  Tax  (Dollars in Thousands)  Amount  Benefit  Amount  2020  Investment Securities:  Change in net unrealized gain (loss) on securities available $  2,437 $  (628) $  1,809 Amortization of losses on securities transferred from available held to maturity  36 (9) 27 Total Investment 2,473 (637) 1,836 Derivative:  Change in net unrealized gain (loss) on effective $  574 $  (146) $  428 Benefit Plans:  Reclassification adjustment for amortization of prior service (880) 223 (657) Reclassification adjustment for amortization of net loss  4,391 (1,113) 3,278 Current year actuarial loss  (27,924) 7,078 (20,846) Total Benefit Plans  (24,413) 6,188 (18,225) Total Other Comprehensive $  (21,366) $  5,405 $  (15,961) 2019  Investment Securities:  Change in net unrealized gain (loss) on securities available $  3,790 $  (950) $  2,840 Amortization of losses on securities transferred from available held to maturity  43 (11) 32 Total Investment 3,833 (961) 2,872 Benefit Plans:  Reclassification adjustment for amortization of prior service 15 (4) 11 Reclassification adjustment for amortization of net loss  4,623 (1,170) 3,453 Current year actuarial loss  (7,642) 1,940 (5,702) Total Benefit Plans  (3,004) 766 (2,238) Total Other Comprehensive $  829 $  (195) $  634 2018  Investment Securities:  Change in net unrealized gain (loss) on securities available $  (409) $  103 $  (306) Amortization of losses on securities transferred from available held to maturity  55 (14) 41 Total Investment (354) 89 (265) Benefit Plans:  Reclassification adjustment for amortization of prior service 199 (50) 149 Reclassification adjustment for amortization of net loss  5,299 (1,346) 3,953 Current year actuarial loss  (815) 207 (608) Total Benefit Plans  4,683 (1,189) 3,494 Total Other Comprehensive $  4,329 $  (1,100) $  3,229 | 
| Activity in accumulated other comprehensive loss, net of tax | Accumulated other comprehensive loss was comprised of Accumulated  Securities  Other  Available  Interest Rate  Retirement  Comprehensive  for Sale  Swap  Plans  Loss  Balance as of January 1, 2020  $  864 $  - $  (29,045) $  (28,181) Other comprehensive income (loss) during the period  1,836 428 (18,225) (15,961) Balance as of December 31, 2020  $  2,700 $  428 $  (47,270) $  (44,142) Balance as of January 1, 2019  $  (2,008) $  -  $  (26,807) $  (28,815) Other comprehensive income (loss) during the period  2,872 -  (2,238) 634 Balance as of December 31, 2019  $  864 $  -  $  (29,045) $  (28,181) Balance as of January 1, 2018  $  (1,743) $  -  $  (30,301) $  (32,044) Other comprehensive (loss) income during the period  (265) -  3,494 3,229  Balance as of December 31, 2018  $  (2,008) $  -  $  (26,807) $  (28,815) |