PREFERRED STOCK AND TEMPORARY EQUITY -Narrative (Details) - $ / shares	Dec. 31, 2018	Dec. 31, 2017	Jan. 29, 2016
Class of Stock [Line Items]
Preferred stock, shares authorized	50,000,000
Preferred stock, par value (in dollars per share)	$ 0.001
Series A Preferred
Class of Stock [Line Items]
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares issued	419,859	453,567
Preferred stock, shares outstanding	419,859	453,567
Series B Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares authorized	10,000,000
Preferred stock, shares issued	3,604,827	3,427,597
Preferred stock, shares outstanding	3,604,827	3,427,597
Series B1 Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares authorized	17,000,000
Preferred stock, shares issued	10,057,597	13,151,989
Preferred stock, shares outstanding	10,057,597	13,151,989
Series C Preferred
Class of Stock [Line Items]
Preferred stock, shares authorized	44,000	44,000
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001	$ 100
Preferred stock, shares issued	0	31,568	44,000
Preferred stock, shares outstanding	0	31,568