Annual report pursuant to Section 13 and 15(d)

SHARE-BASED COMPENSATION - Weighted-average Assumptions (Details)

v3.21.1
SHARE-BASED COMPENSATION - Weighted-average Assumptions (Details) - Stock options
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected dividend yield 0.00% 0.00%
Expected volatility   80.00%
Minimum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected term 1 month 20 days 2 years 9 months 14 days
Risk-free interest rate 0.22% 1.30%
Expected volatility 85.00%  
Maximum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected term 5 years 5 years
Risk-free interest rate 0.41% 2.70%
Expected volatility 90.00%