PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS (Components of cost) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Components of net periodic benefit cost
Pension settlement expense	$ 700	$ 600	$ 2,701	$ 1,464
Nonunion Defined Benefit Pension Plan
Components of net periodic benefit cost
Interest cost	1,149	1,158	2,389	2,463
Expected return on plan assets	(2,054)	(2,158)	(4,221)	(4,104)
Pension settlement expense	744	564	2,701	1,464
Amortization of net actuarial loss	757	1,061	1,643	2,017
Net periodic benefit cost	596	625	2,512	1,840
Supplemental Benefit Plan
Components of net periodic benefit cost
Interest cost	25	33	51	65
Amortization of net actuarial loss	21	38	41	76
Net periodic benefit cost	46	71	92	141
Postretirement Health Benefit Plan
Components of net periodic benefit cost
Service cost	122	107	244	214
Interest cost	265	255	530	509
Amortization of prior service credit	(48)	(48)	(95)	(95)
Amortization of net actuarial loss	174	176	347	352
Net periodic benefit cost	$ 513	$ 490	$ 1,026	$ 980