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COMMITMENTS AND CONTINGENCIES (Details)
$ in Millions
1 Months Ended
Sep. 30, 2017
USD ($)
party
Jun. 30, 2017
party
Jul. 31, 2016
USD ($)
Dec. 31, 2017
USD ($)
Site Contingency [Line Items]        
Purchase commitments       $ 30.2
Koppers Pond [Member]        
Site Contingency [Line Items]        
Clean-up phase cost     $ 1.9  
Number of parties added to cost sharing agreement (party) | party   2    
Number of potentially responsible parties (party) | party 9      
Percentage of costs allocated to company 10.75%      
Accrual for environmental loss contingencies $ 0.2