ACCUMULATED OTHER COMPREHENSIVE INCOME OR LOSS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2018
Summary of changes in accumulated other comprehensive income or loss by component, net of tax [Roll Forward]
Beginning balance	$ 165,029	$ 149,813	$ 143,748
Adjusted cumulative effect of accounting change				$ (162)
Balances as adjusted				149,651
Other comprehensive income before reclassification	5,561	(1,559)	2,200
Amounts reclassified from accumulated other comprehensive income (loss)	51	690	51
Total other comprehensive income (loss)	5,612	(869)	2,251
Stranded AOCI reclassification			0
Ending balance	182,627	165,029	149,813
Realized gains on securities available for sale	19	0	109
Income tax expense	(3,434)	(4,009)	(7,262)
Pension and other employee benefits	5,902	5,524	5,510
Net of tax	15,609	19,626	7,430
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	51	690	51
Total
Summary of changes in accumulated other comprehensive income or loss by component, net of tax [Roll Forward]
Beginning balance	(11,411)	(10,340)	(10,754)
Adjusted cumulative effect of accounting change				(202)
Balances as adjusted				(10,542)
Total other comprehensive income (loss)	5,612	(869)	2,251
Stranded AOCI reclassification			(1,837)
Ending balance	(5,799)	(11,411)	(10,340)
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	(4,646)	(3,415)	(4,356)
Adjusted cumulative effect of accounting change				(202)
Balances as adjusted				(3,617)
Other comprehensive income before reclassification	6,028	(1,029)	1,578
Amounts reclassified from accumulated other comprehensive income (loss)	(14)	0	(68)
Total other comprehensive income (loss)	6,014	(1,029)	1,510
Stranded AOCI reclassification			(569)
Ending balance	1,368	(4,646)	(3,415)
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	(19)	0	(109)
Income tax expense	5	0	41
Net of tax	(14)	0	(68)
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	(6,765)	(6,925)	(6,398)
Balances as adjusted				$ (6,925)
Other comprehensive income before reclassification	(467)	(530)	622
Amounts reclassified from accumulated other comprehensive income (loss)	65	690	119
Total other comprehensive income (loss)	(402)	160	741
Stranded AOCI reclassification			(1,268)
Ending balance	(7,167)	(6,765)	(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	(27)	(236)	(74)
Net of tax	65	690	119
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	$ 312	$ 1,146	$ 413