INCOME TAXES - Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Gross unrecognized tax benefit - beginning balance	$ 2,539	$ 1,797	$ 940
Increases related to tax positions from prior years	0	0	172
Increases related to tax positions taken during current year	777	742	685
Gross unrecognized tax benefit - ending balance	$ 3,316	$ 2,539	$ 1,797