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Stock option plans - Summary (Details) - 2019 Equity Incentive Plan - USD ($)
12 Months Ended
Dec. 31, 2022
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Stock option plan        
Options outstanding 480,274 229,308 188,552 174,975
Shares available for grant 87,856      
Stock based compensation expense $ 16,981,266 $ 7,813,743 $ 4,983,023  
Unrecognized compensation cost $ 487,730      
Recognition period for unrecognized compensation cost 3 years 7 months 6 days