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General. Assumptions for Black-Scholes Option Pricing Model (Details)
9 Months Ended
Sep. 30, 2021
$ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Value of ADS $ 27.26
Dividend yield 0.00%
Expected volatility 70.88%
Minimum [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Risk-free interest rate 1.36%
Expected term (years) 5 years 8 months 12 days
Maximum [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Risk-free interest rate 1.61%
Expected term (years) 6 years 1 month 6 days