PENSION AND OTHER POSTRETIREMENT PLANS - Net pension expense and other amounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net pension expense:
Net (gain)/loss	$ 409	$ (269)	$ (97)
Pension Benefits
Net pension expense:
Service cost	0	0	0
Interest cost	87	93	104
Expected return on plan assets	(137)	(138)	(143)
Recognized net actuarial loss	132	193	185
Settlement cost	0	224	0
Net pension expense	82	372	146
Net (gain)/loss	353	(296)	(36)
Amortization of net loss	(132)	(193)	(185)
Total recognized in other comprehensive income (loss)	221	(489)	(221)
Total recognized in net pension expense and other comprehensive income (loss)	303	(117)	(75)
SERP Benefits
Net pension expense:
Service cost	0	0	0
Interest cost	37	34	40
Expected return on plan assets	(55)	(61)	(63)
Recognized net actuarial loss	73	73	80
Settlement cost	0	0	0
Net pension expense	55	46	57
Net (gain)/loss	56	27	(61)
Amortization of net loss	(73)	(73)	(80)
Total recognized in other comprehensive income (loss)	(17)	(46)	(141)
Total recognized in net pension expense and other comprehensive income (loss)	$ 38	$ 0	$ (84)