SHARE-BASED COMPENSATION - Expense (Details) - Stock options - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Employees And Directors
Share-Based Compensation Awards
Stock-based compensation expenses	$ 952	$ 318
Employees And Directors | Research and development expense
Share-Based Compensation Awards
Stock-based compensation expenses	169	65		$ 124
Employees And Directors | General and administrative expense
Share-Based Compensation Awards
Stock-based compensation expenses	$ 783	$ 253		366
Employees, non-employees, directors
Share-Based Compensation Awards
Stock-based compensation expenses			$ 1,800	490
Employees, non-employees, directors | Research and development expense
Share-Based Compensation Awards
Stock-based compensation expenses			314
Employees, non-employees, directors | General and administrative expense
Share-Based Compensation Awards
Stock-based compensation expenses			$ 1,486
Nonemployees | Research and development expense
Share-Based Compensation Awards
Stock-based compensation expenses				$ 585