STOCKHOLDERS' DEFICIT - Carrying Value of Preferred Stock Narrative (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
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	100
Convertible preferred stock series, liquidation preference	$ 3,172	$ 2,916
Series C Preferred Stock
Class of Warrant or Right [Line Items]
Dividend accrual rate	11.50%
Accretion of dividends on preferred stock	$ 7,500
Discount accretion on preferred stock	500
Convertible preferred stock series, liquidation preference	$ 92,038	$ 84,555