PENSION AND OTHER POSTRETIREMENT PLANS - Changes in Obligations and Plan Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Benefits
Change in benefit obligation:
Benefit obligation at beginning of year	$ 24,759	$ 20,844
Service cost	1,106	1,129	$ 1,153
Interest cost	794	750	794
Benefits paid and expected expenses	(402)	(285)
Assumption changes and other	(2,646)	2,321
Benefit obligation at end of year	23,611	24,759	20,844
Change in plan assets:
Fair value of plan assets at beginning of year	34,695	27,914
Actual return on plan assets	(2,079)	4,859
Employer contribution	1,660	2,207
Benefits paid and actual expenses	(402)	(285)
Fair value of plan assets at end of year	33,874	34,695	27,914
Funded status at end of year	10,263	9,936
SERP Benefits
Change in benefit obligation:
Benefit obligation at beginning of year	3,919	3,004
Service cost	290	212	176
Interest cost	127	105	105
Benefits paid and expected expenses	(112)	(112)
Assumption changes and other	(413)	710
Benefit obligation at end of year	3,811	3,919	$ 3,004
Change in plan assets:
Fair value of plan assets at beginning of year	0
Actual return on plan assets	0	0
Employer contribution	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	$ (3,811)	$ (3,919)