SHARE-BASED COMPENSATION - Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Share-Based Compensation Awards
Stock-based compensation expenses	$ 4,657	$ 1,381
Stock options | Employees
Share-Based Compensation Awards
Stock-based compensation expenses	4,581	1,381
Stock options | Employees | Research and development expense
Share-Based Compensation Awards
Stock-based compensation expenses	933	276
Stock options | Employees | General and administrative expense
Share-Based Compensation Awards
Stock-based compensation expenses	3,647	1,105
RSUs
Share-Based Compensation Awards
Stock-based compensation expenses	76	$ 0
RSUs | Research and development expense
Share-Based Compensation Awards
Stock-based compensation expenses	69
RSUs | General and administrative expense
Share-Based Compensation Awards
Stock-based compensation expenses	7
RSUs | Employees
Share-Based Compensation Awards
Stock-based compensation expenses	76
RSUs | Employees | Research and development expense
Share-Based Compensation Awards
Stock-based compensation expenses	69
RSUs | Employees | General and administrative expense
Share-Based Compensation Awards
Stock-based compensation expenses	$ 7