PENSION AND POSTRETIREMENT PLANS (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Pension Benefits
Components of net periodic benefit cost and other amounts recognized in Other Comprehensive Income
Service cost	$ 325	$ 292	$ 650	$ 585
Interest cost	198	186	395	370
Expected return on plan assets	(625)	(520)	(1,250)	(1,040)
Amortization of net loss	82	112	165	225
Amortization of prior service credit	(19)	(19)	(38)	(38)
Amortization of transition obligation	0	0	0	0
Net periodic benefit (credit) cost	(39)	51	(78)	102
SERP Benefits
Components of net periodic benefit cost and other amounts recognized in Other Comprehensive Income
Service cost	72	52	145	105
Interest cost	31	26	63	52
Expected return on plan assets	0	0	0	0
Amortization of net loss	31	13	61	26
Amortization of prior service credit	0	0	0	0
Amortization of transition obligation	1	7	2	14
Net periodic benefit (credit) cost	$ 135	$ 98	$ 271	$ 197