SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Stock-based compensation expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Stock-based compensation expense	$ 1,308	$ 1,881	$ 3,494	$ 5,425
Options
Stock-based compensation expense	98	143	308	518
Restricted Stock Units
Stock-based compensation expense	1,145	1,602	3,022	4,484
Common Stock
Stock-based compensation expense	$ 65	$ 136	$ 164	$ 423