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 (credit)
Service cost	$ 505	$ 487
Interest cost	1,385	1,498
Expected return on plan assets	(2,224)	(2,110)
Amortization of prior service credit	(81)	(76)
Amortization of transition asset	0	0
Amortization of loss (gain)	805	932
Settlement loss (gain)	10	0
Net periodic cost	400	731
Postretirement Benefits
Components of net periodic benefit cost (credit)
Service cost	3	3
Interest cost	16	18
Expected return on plan assets	0	0
Amortization of prior service credit	0	0
Amortization of transition asset	0	0
Amortization of loss (gain)	(10)	(11)
Settlement loss (gain)	0	0
Net periodic cost	$ 9	$ 10