PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS (Nonunion) (Details) $ in Thousands	3 Months Ended			6 Months Ended	9 Months Ended
	Sep. 30, 2017 USD ($)	Mar. 31, 2017 USD ($) person	Sep. 30, 2016 USD ($)	Jun. 30, 2017	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)
Pension and other postretirement benefit plans
Pension settlement expense, pre-tax					$ 3,644	$ 2,267
Pension settlement expense, net of tax	$ 577		$ 490		2,227	1,385
Nonunion Defined Benefit Pension Plan
Pension and other postretirement benefit plans
Expected return on plan assets (as a percent)	2.50%			6.50%
Number of plan participants for which vested pension benefits were settled | person		50
Pension settlement expense, pre-tax	$ 943		803		3,644	2,267
Pension settlement expense, net of tax	600		500		2,200	1,400
Lump-sum distributions	$ 5,800		$ 4,300		$ 15,500	$ 11,600
Premium paid to purchase nonparticipating annuity contract		$ 7,600