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EMPLOYEE BENEFIT PLANS (Plans) (Details)
$ in Thousands
 3 Months Ended 12 Months Ended
Mar. 31, 2017
USD ($)
person
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Nonunion Defined Benefit Pension Plan      
Nonunion Defined Benefit Pension, Supplemental Benefit, and Postretirement Health Benefit Plans      
Premium paid to purchase nonparticipating annuity contract $ 7,600 $ 7,600  
Number of plan participants for which vested pension benefits were settled | person 50    
Unrecognized net actuarial loss   $ 22,588 $ 23,294
Amortization period for unrecognized net actuarial loss   8 years  
Lump-sum distributions   $ 18,700  
Postretirement Health Benefit Plan      
Nonunion Defined Benefit Pension, Supplemental Benefit, and Postretirement Health Benefit Plans      
Unrecognized net actuarial loss   $ 2,764 $ 5,708
Unrecognized prior service credit, amortization period   9 years