STOCK BASED COMPENSATION - Stock-based compensation expense (Details) - USD ($) $ in Thousands |
12 Months Ended | |
|---|---|---|
Dec. 31, 2021 |
Dec. 31, 2020 |
|
| Stock-based compensation | ||
| Total stock-based compensation expense | $ 11,177 | $ 8,026 |
| Research and development | ||
| Stock-based compensation | ||
| Total stock-based compensation expense | 2,759 | 2,580 |
| General and administrative | ||
| Stock-based compensation | ||
| Total stock-based compensation expense | $ 8,418 | $ 5,446 |