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OTHER LONG-TERM LIABILITIES
12 Months Ended
Dec. 31, 2017
Other Liabilities Disclosure [Abstract]  
OTHER LONG-TERM LIABILITIES
OTHER LONG-TERM LIABILITIES
Other long-term liabilities consisted of the following:
 
 
December 31,
2017
 
December 31,
2016
Defined benefit pension plan liabilities
 
$
63,579

 
$
60,141

Post-retirement medical plan liabilities
 
21,527

 
22,740

Environmental liabilities
 
140,403

 
145,928

Other
 
250

 
226

Total other long-term liabilities
 
$
225,759

 
$
229,035