INCOME TAXES - Summary of Changes in Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits balance, January 1,	$ 162	$ 187	$ 0
Addition for tax positions taken in a prior year	300	162	187
Deduction for tax positions taken in a prior year	0	(187)	0
Unrecognized tax benefits balance, December 31,	$ 462	$ 162	$ 187