Quarterly report pursuant to Section 13 or 15(d)

stock-based compensation (Details)

v3.21.2
stock-based compensation (Details) - Stock Option Plan 2015 [Member] - Time Based Shares Options [Member] - USD ($)
9 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Dividend yield 0.00% 0.00%
Weighted-average volatility 0.00% 0.00%
Expected dividends $ 0 $ 0
Expected term (in years) 10 years 10 years
Minimum [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected Volatility 74.01% 62.11%
Risk-free rate 1.20% 0.63%
Maximum [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected Volatility 76.77% 62.18%
Risk-free rate 1.62% 0.64%