PREFERRED STOCK AND STOCKHOLDERS' DEFICIT - Carrying Value of Preferred Stock Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 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	$ 100
Discount accretion on preferred stock	14
Convertible preferred stock series, liquidation preference	$ 3,356	$ 3,264
Series C Preferred Stock
Class of Warrant or Right [Line Items]
Dividend accrual rate	11.50%
Accretion of dividends on preferred stock	$ 2,700
Discount accretion on preferred stock	200
Convertible preferred stock series, liquidation preference	$ 97,391	$ 94,706