INCOME TAXES - Unrecognized Tax Benefit (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits [Roll Forward]
Unrecognized tax benefits, beginning balance	$ 1,021	$ 1,067	$ 1,096
Lapse of statute of limitations	(7)	(46)	(29)
Unrecognized tax benefits, ending balance	$ 1,014	$ 1,021	$ 1,067