ACCOUNTS RECEIVABLE - Allowances (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning	$ (2,234)	$ (2,437)	$ (2,494)
Additions	(418)	0	(235)
Write-offs	306	203	292
Ending	$ (2,346)	$ (2,234)	$ (2,437)