PENSION AND OTHER POSTRETIREMENT PLANS - Changes in Obligations and Plan Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Benefits
Change in benefit obligation:
Benefit obligation at beginning of year	$ 23,611	$ 24,759
Service cost	952	1,106	$ 1,129
Interest cost	908	794	750
Benefits paid and expected expenses	(475)	(402)
Assumption changes and other	3,761	(2,646)
Benefit obligation at end of year	28,757	23,611	24,759
Change in plan assets:
Fair value of plan assets at beginning of year	33,874	34,695
Actual return on plan assets	6,346	(2,079)
Contribution to the plan		1,660
Benefits paid and actual expenses	(475)	(402)
Fair value of plan assets at end of year	39,745	33,874	34,695
Funded status at end of year	10,988	10,263
SERP Benefits
Change in benefit obligation:
Benefit obligation at beginning of year	3,811	3,919
Service cost	261	290	212
Interest cost	147	127	105
Benefits paid and expected expenses	(112)	(112)
Assumption changes and other	1,216	(413)
Benefit obligation at end of year	5,323	3,811	$ 3,919
Change in plan assets:
Fair value of plan assets at beginning of year	0
Actual return on plan assets	0	0
Contribution to the plan	112	112
Benefits paid and actual expenses	(112)	(112)
Fair value of plan assets at end of year	0	0
Funded status at end of year	$ (5,323)	$ (3,811)