SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Allowance for doubtful accounts	$ 1,226	$ 757	$ 643	$ 1,182
Bad debt (recovery) expense	(340)	886	(23)
Increase (reduction) in allowance for doubtful accounts	$ 809	$ (772)	$ (516)