INCOME TAXES - NET DEFERRED TAX ASSET (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Significant components of net deferred tax asset
Net operating loss carryforward	$ 30,014	$ 22,490
Research and development credit carryforward	942	801
Stock-based compensation	3,307	2,265
Depreciation and amortization	(48)	(124)
Accrued expenses	186	226
Charitable contributions	96	112
Subtotal	34,497	25,770
Valuation allowance	(34,497)	(25,770)
Increase in valuation allowance	8,727	6,290
Uncertain tax positions	$ 0	$ 0