PENSION AND POSTRETIREMENT PLANS (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Pension Benefits
Components of net periodic benefit cost and other amounts recognized in Other Comprehensive Income
Service cost	$ 325	$ 293
Interest cost	197	184
Expected return on plan assets	(625)	(520)
Amortization of net loss	83	113
Amortization of prior service credit	(19)	(19)
Amortization of transition obligation	0	0
Net periodic benefit (credit) cost	(39)	51
SERP Benefits
Components of net periodic benefit cost and other amounts recognized in Other Comprehensive Income
Service cost	73	53
Interest cost	32	26
Expected return on plan assets	0	0
Amortization of net loss	30	13
Amortization of prior service credit	0	0
Amortization of transition obligation	1	7
Net periodic benefit (credit) cost	$ 136	$ 99