BENEFIT PLANS (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Pension Benefits [Member]
Net periodic benefit cost [Abstract]
Service cost	$ 1,121	$ 1,039
Interest cost	1,415	1,361
Expected return on plan assets	(3,705)	(3,121)
Amortization of unrecognized net loss	298	263
Amortization of prior service cost	(83)	14
Net periodic benefit	(954)	(444)
Post-retirement Benefits [Member]
Net periodic benefit cost [Abstract]
Service cost	0	0
Interest cost	17	19
Expected return on plan assets	0	0
Amortization of unrecognized net loss	5	2
Amortization of prior service cost	(44)	(45)
Net periodic benefit	$ (22)	$ (24)