SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Stock compensation expense (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	$ 1,041	$ 1,763	$ 2,186	$ 3,544
Stock Options
Stock-based compensation expense	103	226	210	375
Restricted Stock Units
Stock-based compensation expense	889	1,284	1,877	2,882
Common Stock
Stock-based compensation expense	$ 49	$ 253	$ 99	$ 287