PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS (Nonunion) (Details) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($) person	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)
Pension and other postretirement benefit plans
Pension settlement expense, pre-tax				$ 1,085	$ 2,701
Pension settlement expense, net of tax	$ 320	$ 454		806	1,650
Nonunion Defined Benefit Pension Plan
Pension and other postretirement benefit plans
Pension settlement expense, pre-tax	431	744		1,085	2,701
Pension settlement expense, net of tax	300	500		800	1,700
Lump-sum distributions	$ 3,700	$ 4,900		$ 8,500	$ 9,700
Premium paid to purchase nonparticipating annuity contract			$ 7,600
Number of plan participants for which vested pension benefits were settled | person			50