PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS (Components of cost) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Components of net periodic benefit cost
Pension settlement expense	$ 654	$ 1,957
Nonunion Defined Benefit Pension Plan
Components of net periodic benefit cost
Interest cost	1,015	1,240
Expected return on plan assets	(401)	(2,167)
Pension settlement expense	654	1,957
Amortization of net actuarial loss	778	886
Net periodic benefit cost	2,046	1,916
Supplemental Benefit Plan
Components of net periodic benefit cost
Interest cost	27	26
Amortization of net actuarial loss	20	20
Net periodic benefit cost	47	46
Postretirement Health Benefit Plan
Components of net periodic benefit cost
Service cost	92	122
Interest cost	209	265
Amortization of prior service credit	(23)	(47)
Amortization of net actuarial loss	76	173
Net periodic benefit cost	$ 354	$ 513