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PENSION AND OTHER POSTRETIREMENT BENEFITS - DEFINED CONTRIBUTION PLAN (Details)
$ in Millions
12 Months Ended
Dec. 31, 2016
USD ($)
$ / employees
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Defined Benefit Plan Disclosure [Line Items]      
Amount expensed and contributed for matching provision of Savings Plan | $ $ 2.3 $ 2.1 $ 2.0
Employees eligible for defined benefit pension plan      
Defined Benefit Plan Disclosure [Line Items]      
Matching percentage of participants' contributions 50.00%    
Percentage of base compensation (up to) 6.00%    
Employees ineligible for defined benefit pension plan      
Defined Benefit Plan Disclosure [Line Items]      
Matching percentage of participants' contributions 50.00%    
Percentage of base compensation (up to) 8.00%    
Year-end contribution (in dollars per employee) 1,500    
Service threshold to determine year-end contribution (up to, more than) 10 years    
Year-end contribution (in dollars per employee) 2,000