ACCUMULATED OTHER COMPREHENSIVE INCOME OR LOSS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Summary of changes in accumulated other comprehensive income or loss by component, net of tax [Roll Forward]
Beginning balance	$ 182,627	$ 165,029	$ 149,813
Other comprehensive income before reclassification	8,136	5,561	(1,559)
Amounts reclassified from accumulated other comprehensive income (loss)	64	51	690
Total other comprehensive income (loss)	8,200	5,612	(869)
Ending balance	199,699	182,627	165,029
Realized gains on securities available for sale	0	19	0
Income tax expense	4,607	3,434	4,009
Pension and other employee benefits	5,553	5,902	5,524
Net of tax	19,262	15,609	19,626
Cumulative Effect, Period of Adoption, Adjusted Balance
Summary of changes in accumulated other comprehensive income or loss by component, net of tax [Roll Forward]
Beginning balance			149,651
Reclassification out of Accumulated Other Comprehensive Income (loss)
Summary of changes in accumulated other comprehensive income or loss by component, net of tax [Roll Forward]
Net of tax	65	51	690
Total
Summary of changes in accumulated other comprehensive income or loss by component, net of tax [Roll Forward]
Beginning balance	(5,799)	(11,411)	(10,340)
Total other comprehensive income (loss)	8,200	5,612	(869)
Ending balance	2,401	(5,799)	(11,411)
Total | Cumulative Effect, Period of Adoption, Adjustment
Summary of changes in accumulated other comprehensive income or loss by component, net of tax [Roll Forward]
Beginning balance			(202)
Total | Cumulative Effect, Period of Adoption, Adjusted Balance
Summary of changes in accumulated other comprehensive income or loss by component, net of tax [Roll Forward]
Beginning balance			(10,542)
Total | Reclassification out of Accumulated Other Comprehensive Income (loss)
Summary of changes in accumulated other comprehensive income or loss by component, net of tax [Roll Forward]
Net of tax	0	(14)	0
Unrealized Gains and Losses on Securities Available for Sale
Summary of changes in accumulated other comprehensive income or loss by component, net of tax [Roll Forward]
Beginning balance	1,368	(4,646)	(3,415)
Other comprehensive income before reclassification	7,759	6,028	(1,029)
Amounts reclassified from accumulated other comprehensive income (loss)	0	(14)	0
Total other comprehensive income (loss)	7,759	6,014	(1,029)
Ending balance	9,127	1,368	(4,646)
Unrealized Gains and Losses on Securities Available for Sale | Cumulative Effect, Period of Adoption, Adjustment
Summary of changes in accumulated other comprehensive income or loss by component, net of tax [Roll Forward]
Beginning balance			(202)
Unrealized Gains and Losses on Securities Available for Sale | Cumulative Effect, Period of Adoption, Adjusted Balance
Summary of changes in accumulated other comprehensive income or loss by component, net of tax [Roll Forward]
Beginning balance			(3,617)
Unrealized Gains and Losses on Securities Available for Sale | Reclassification out of Accumulated Other Comprehensive Income (loss)
Summary of changes in accumulated other comprehensive income or loss by component, net of tax [Roll Forward]
Realized gains on securities available for sale	0	(19)	0
Income tax expense	0	5	0
Defined Benefit and Other Benefit Plans
Summary of changes in accumulated other comprehensive income or loss by component, net of tax [Roll Forward]
Beginning balance	(7,167)	(6,765)	(6,925)
Other comprehensive income before reclassification	377	(467)	(530)
Amounts reclassified from accumulated other comprehensive income (loss)	64	65	690
Total other comprehensive income (loss)	441	(402)	160
Ending balance	(6,726)	(7,167)	(6,765)
Defined Benefit and Other Benefit Plans | Cumulative Effect, Period of Adoption, Adjustment
Summary of changes in accumulated other comprehensive income or loss by component, net of tax [Roll Forward]
Beginning balance			0
Defined Benefit and Other Benefit Plans | Cumulative Effect, Period of Adoption, Adjusted Balance
Summary of changes in accumulated other comprehensive income or loss by component, net of tax [Roll Forward]
Beginning balance			(6,925)
Defined Benefit and Other Benefit Plans | Reclassification out of Accumulated Other Comprehensive Income (loss)
Summary of changes in accumulated other comprehensive income or loss by component, net of tax [Roll Forward]
Income tax expense	(15)	(27)	(236)
Net of tax	65	65	690
Net Prior Service Cost (Credit) | Reclassification out of Accumulated Other Comprehensive Income (loss)
Summary of changes in accumulated other comprehensive income or loss by component, net of tax [Roll Forward]
Pension and other employee benefits	(220)	(220)	(220)
Net Unamortized Gain (Loss) | Reclassification out of Accumulated Other Comprehensive Income (loss)
Summary of changes in accumulated other comprehensive income or loss by component, net of tax [Roll Forward]
Pension and other employee benefits	$ 300	$ 312	$ 1,146