PENSION AND OTHER POST-EMPLOYMENT BENEFITS (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Pension Benefits
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Service cost	$ 235	$ 175
Interest cost	2,504	2,390
Expected return on plan assets	(4,606)	(4,615)
Amortization of prior service credit	0	0
Recognized actuarial loss (gain)	366	154
Net periodic benefit income	(1,501)	(1,896)
Other Benefits
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Service cost	0	0
Interest cost	30	43
Expected return on plan assets	0	0
Amortization of prior service credit	(182)	(371)
Recognized actuarial loss (gain)	(18)	1
Net periodic benefit income	$ (170)	$ (327)