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HEALTH, SAFETY AND ENVIRONMENTAL MATTERS Table 2 - Accruals for Environmental Matters (Details) - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Accrual for Environmental Loss Contingencies, Balance Sheet Classification [Abstract]      
Accrued liabilities $ 3,054 $ 3,281  
Other long-term liabilities 2,629 1,839  
Accruals for environmental matters $ 5,683 $ 5,120 $ 7,667