SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - STOCK BASED COMPENSATION (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Stock-Based Compensation Expense
Stock-based compensation expense included in operating expenses	$ 2,058	$ 1,973	$ 3,750	$ 3,767
Research and development
Stock-Based Compensation Expense
Stock-based compensation expense included in operating expenses	1,012	906	1,867	1,731
General and administrative
Stock-Based Compensation Expense
Stock-based compensation expense included in operating expenses	$ 1,046	$ 1,067	$ 1,883	$ 2,036