SHARE-BASED COMPENSATION - Share-based Compensation Expense (Details) - USD ($) $ in Thousands |
12 Months Ended | |
|---|---|---|
Dec. 31, 2019 |
Dec. 31, 2018 |
|
| Total share-based compensation | $ 2,871 | $ 3,805 |
| Research and development | ||
| Total share-based compensation | 908 | 2,445 |
| General and administrative | ||
| Total share-based compensation | $ 1,963 | $ 1,360 |