PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS (Components of cost) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Components of net periodic benefit cost
Pension settlement expense	$ 89	$ 1,356
Nonunion Defined Benefit Pension Plan
Components of net periodic benefit cost
Interest cost		318
Expected return on plan assets		(90)
Pension settlement expense		1,356
Amortization of net actuarial (gain) loss		149
Net periodic benefit cost		1,733
Supplemental Benefit Plan
Components of net periodic benefit cost
Interest cost	3	10
Pension settlement expense	89
Amortization of net actuarial (gain) loss	4	24
Net periodic benefit cost	96	34
Postretirement Health Benefit Plan
Components of net periodic benefit cost
Service cost	47	80
Interest cost	144	303
Amortization of prior service credit		(9)
Amortization of net actuarial (gain) loss	(149)	225
Net periodic benefit cost	$ 42	$ 599