OTHER NON-CURRENT LIABILITIES (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Other Liabilities, Noncurrent [Abstract]
Accrued employee benefit liabilities	$ 28,246	$ 31,969
Accrued environmental remediation liabilities	27,358	31,803
Deferred consideration	20,232	19,640
ARO	4,349	3,833
Other	4,715	5,411
Total other non-current liabilities	$ 84,900	$ 92,656