ACCUMULATED OTHER COMPREHENSIVE LOSS - Details about Accumulated Other Comprehensive Income Components (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net gains on security transactions	$ 0	$ 0	$ 19	$ 0
Income tax expense (benefit)	176	1,802	2,443	3,349
Pension and other employee benefits	1,470	1,262	4,488	4,438
Net income	1,956	6,930	11,405	13,896
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income	13	13	26	40
Unrealized Gains and Losses on Securities Available for Sale | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net gains on security transactions	0	0	(19)	0
Income tax expense (benefit)	0	0	5	0
Net income	0	0	(14)	0
Prior service costs | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Pension and other employee benefits	(55)	(55)	(165)	(165)
Actuarial losses | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Pension and other employee benefits	72	72	218	218
Defined Benefit and Other Benefit Plans | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense (benefit)	(4)	(4)	(13)	(13)
Net income	$ 13	$ 13	$ 40	$ 40