PREFERRED STOCK AND STOCKHOLDERS' DEFICIT - Carrying Value of Preferred Stock Narrative (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Series A Preferred Stock
Class of Warrant or Right [Line Items]
Dividend accrual rate	11.50%
Accretion of dividends on preferred stock	$ 200
Discount accretion on preferred stock	22
Convertible preferred stock series, liquidation preference	$ 3,452	$ 3,264
Series C Preferred Stock
Class of Warrant or Right [Line Items]
Dividend accrual rate	11.50%
Accretion of dividends on preferred stock	$ 5,500
Discount accretion on preferred stock	300
Convertible preferred stock series, liquidation preference	$ 100,184	$ 94,706