PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS (Nonunion) (Details) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) person	Jun. 30, 2016 USD ($)
Pension and other postretirement benefit plans
Pension settlement expense, pre-tax	$ 700		$ 600	$ 2,701	$ 1,464
Pension settlement expense, net of tax	454		345	$ 1,650	895
Nonunion Defined Benefit Pension Plan
Pension and other postretirement benefit plans
Number of plan participants for which vested pension benefits were settled | person				50
Pension settlement expense, pre-tax	744		564	$ 2,701	1,464
Pension settlement expense, net of tax	500		300	1,700	900
Lump-sum distributions	$ 4,900		$ 2,700	$ 9,700	$ 7,200
Premium paid to purchase nonparticipating annuity contract		$ 7,600