INCOME TAXES - Components of provision for income taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal	$ 470	$ 1,807	$ (807)
State	70	410	280
Total current tax	540	2,217	(527)
Deferred:
Federal	436	(120)	(16)
State	(11)	(12)	7
Total deferred tax	425	(132)	(9)
Provision for (benefit from) income taxes	$ 965	$ 2,085	$ (536)