PENSION AND OTHER POSTRETIREMENT PLANS - Components of net periodic benefit cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net pension expense:
Net (gain)/loss	$ 105	$ 409	$ (269)
Pension Benefits
Net pension expense:
Service cost	0	0	0
Interest cost	75	87	93
Expected return on plan assets	(140)	(137)	(138)
Recognized net actuarial (gain) loss	171	132	193
Settlement cost	115	0	224
Net pension expense (benefit)	221	82	372
Net (gain)/loss	69	353	(296)
Defined Benefit Plan, Amount Recognized in Net Periodic Benefit Cost (Credit) and Other Comprehensive (Income) Loss, before Tax	119	303	(117)
Amortization of net loss	(171)	(132)	(193)
Total recognized in other comprehensive income	(102)	221	(489)
SERP Benefits
Net pension expense:
Service cost	0	0	0
Interest cost	27	37	34
Expected return on plan assets	(51)	(55)	(61)
Recognized net actuarial (gain) loss	80	73	73
Settlement cost	0	0	0
Net pension expense (benefit)	56	55	46
Net (gain)/loss	36	56	27
Defined Benefit Plan, Amount Recognized in Net Periodic Benefit Cost (Credit) and Other Comprehensive (Income) Loss, before Tax	12	38	0
Amortization of net loss	(80)	(73)	(73)
Total recognized in other comprehensive income	$ (44)	$ (17)	$ (46)