PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS (Components of cost) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Components of net periodic benefit cost
Pension settlement expense			$ 1,085	$ 2,701
Nonunion Defined Benefit Pension Plan
Components of net periodic benefit cost
Interest cost	$ 1,108	$ 1,149	2,123	2,389
Expected return on plan assets	(378)	(2,054)	(779)	(4,221)
Pension settlement expense	431	744	1,085	2,701
Amortization of net actuarial loss	592	757	1,370	1,643
Net periodic benefit cost	1,753	596	3,799	2,512
Supplemental Benefit Plan
Components of net periodic benefit cost
Interest cost	27	25	54	51
Amortization of net actuarial loss	20	21	40	41
Net periodic benefit cost	47	46	94	92
Postretirement Health Benefit Plan
Components of net periodic benefit cost
Service cost	91	122	183	244
Interest cost	210	265	419	530
Amortization of prior service credit	(24)	(48)	(47)	(95)
Amortization of net actuarial loss	76	174	152	347
Net periodic benefit cost	$ 353	$ 513	$ 707	$ 1,026