STOCK BASED COMPENSATION (Details) - USD ($) $ in Thousands	1 Months Ended		6 Months Ended	12 Months Ended		43 Months Ended
	Jan. 31, 2019	Mar. 31, 2015	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Apr. 30, 2015
Stock options
Aggregate number of shares reserved for issuance			7,738,229	7,738,229		7,738,229
Stock-based compensation (in dollars)				$ 618	$ 4,100
Stock Options
Stock options
Granted (in shares)				15,524	57,579
Expected term				10 years
Aggregate number of shares reserved for issuance			54,849	54,849		54,849
2010 Plan
Stock options
Granted (in shares)						0
Shares available for future grants			12,894	12,894		12,894
Expected term				10 years
2015 Plan
Stock options
Shares available for future grants			188,552	188,552		188,552
Shares authorized for issuance							160,000
Expected term				10 years
2007 Plan
Stock options
Expected term				10 years
Employee Stock Purchase Plan
Stock options
Shares authorized for issuance		7,500
Percentage of outstanding shares reserved for future issuance		1.00%
Increase in shares of common stock reserved for issuance (in shares)		2,000
Aggregate number of shares reserved for issuance			7,923	7,923		7,923
Stock issued under ESPP (in shares)	1,065
Offering Period				6 months
Stock-based compensation (in dollars)				$ 2	$ 14
Employee Stock Purchase Plan | Maximum
Stock options
Aggregate number of shares reserved for issuance		50,000
Common Stock
Stock options
Stock issued under ESPP (in shares)				1,133	710
Accrued expenses | Employee Stock Purchase Plan
Stock options
Employee payroll deductions (in dollars)			$ 1