STOCK-BASED COMPENSATION (Details) - $ / shares	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Common stock and preferred stock
Common stock, authorized	120,000,000	120,000,000
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares issued	24,645,542	24,538,309
Common stock, shares outstanding	24,645,542	24,538,309
Preferred stock, authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Closing price of common stock (as percent)	85.00%
Employee basic pay holding period	6 months
Common stock shares reserved for future issuance	6,211,223	5,117,423
Stock Options
Common stock and preferred stock
Common stock shares reserved for future issuance	219,500
2017 Employee Stock Purchase Plan
Common stock and preferred stock
Number of common stock issuable upon exercise of rights under equity compensation plans	223,341	223,341
2009 plan
Common stock and preferred stock
Number of common stock issuable upon exercise of rights under equity compensation plans	2,649,952	2,868,449
2017 Equity Incentive Plan
Common stock and preferred stock
Common stock shares reserved for future issuance	1,050,649
Number of common stock issuable upon exercise of rights under equity compensation plans	3,118,430	2,025,633
2017 Equity Incentive Plan | Maximum
Common stock and preferred stock
Common stock shares reserved for future issuance	2,649,952
2017 Equity Incentive Plan | Minimum
Common stock and preferred stock
Common stock shares reserved for future issuance		3,573,766
Percentage of aggregate number of common shares reserved for future issuance (as a percent)		4.00%