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Equity - Assumptions used in Valuing the Stock Options Granted under Black-Scholes Valuation Model (Details) - Stock Option
3 Months Ended 9 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Expected dividend yield 0.00% 0.00% 0.00% 0.00%
Expected volatility 97.59% 91.44% 99.30% 87.77%
Risk-free interest rate 0.96% 2.46% 2.73% 1.97%
Expected average life of options 6 years 8 years 5 years 8 years