STOCK-BASED COMPENSATION - Share-based 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 Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	$ 453	$ 299	$ 856	$ 683
Research and development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	68	78	172	156
General and administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	$ 385	$ 221	$ 684	$ 527