EQUITY-BASED COMPENSATION - Compensation expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity-based employee compensation expense	$ 376	$ 517	$ 856	$ 966
Selling, General and Administrative Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity-based employee compensation expense	334	446	772	795
Research and Development Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity-based employee compensation expense	$ 42	$ 71	$ 84	$ 171