PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS (Nonunion) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($) person
Pension and other postretirement benefit plans
Pension settlement expense, pre-tax	$ 654	$ 1,957
Pension settlement expense, net of tax	486	1,196
Nonunion Defined Benefit Pension Plan
Pension and other postretirement benefit plans
Pension settlement expense, pre-tax	654	1,957
Pension settlement expense, net of tax	500	1,200
Lump-sum distributions	$ 4,800	4,800
Premium paid to purchase nonparticipating annuity contract		$ 7,600
Number of plan participants for which vested pension benefits were settled | person		50