INCOME TAXES - Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of beginning and ending amount of unrecognized tax benefits [Roll Forward]
Balance as of January 1	$ 733	$ 715
Additions for tax positions related to the current year	0	90
Additions for tax positions of prior years	0	54
Reductions of tax positions of prior years	(576)	(126)
Balance as of December 31	$ 157	$ 733