PENSION AND OTHER POSTRETIREMENT PLANS - Components of net periodic benefit cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Benefits
Change in benefit obligation:
Beginning benefit obligation	$ 2,118	$ 2,862
Interest cost	87	93	$ 104
Actuarial (gain) loss	631	(325)
Benefits paid	(121)	(512)
Ending benefit obligation	2,715	2,118	2,862
Change in plan assets (primarily equity and fixed income investments and money market funds), at fair value:
Beginning plan assets	2,151	2,356
Actual return	415	(61)
Employer contribution	27	368
Benefits paid	(121)	(512)
Ending plan assets	2,472	2,151	2,356
Funded status at end of year	(243)	33
SERP Benefits
Change in benefit obligation:
Beginning benefit obligation	924	1,086
Interest cost	37	34	40
Actuarial (gain) loss	164	(62)
Benefits paid	(134)	(134)
Ending benefit obligation	991	924	1,086
Change in plan assets (primarily equity and fixed income investments and money market funds), at fair value:
Beginning plan assets	885	1,047
Actual return	163	(28)
Employer contribution	0	0
Benefits paid	(134)	(134)
Ending plan assets	914	885	$ 1,047
Funded status at end of year	$ (77)	$ (39)