INCOME TAXES - Net Operating Loss Carryforwards (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Unregnized tax benefit roll forward
Unrecognized tax benefits, beginning balance	$ 1,625	$ 1,625	$ 0
Gross increases - tax positions in current period	0	0	1,625
Unrecognized tax benefits, ending balance	$ 1,625	$ 1,625	$ 1,625