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Share-based compensation - Additional Information (Details) - USD ($)
9 Months Ended 12 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Dec. 31, 2020
Jun. 11, 2020
Jun. 07, 2018
Sep. 17, 2014
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]            
Share based compensation expense $ 500,000 $ 600,000        
Common stock reserved for issuance 3,739,235          
Options granted 463,754 254,700 254,700      
Stock option vesting period 2 years          
Share-based compensation arrangement by share based payment award percentage of fair market Person holding more then 10% voting stock 110.00%          
Intrinsic value of options outstanding $ 10,700,000   $ 700,000      
Intrinsic value of options unvested 5,700   $ 0      
Intrinsic value of options exercised $ 2,100,000 $ 0        
Minimum            
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]            
Contractual term 3 years          
Maximum            
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]            
Contractual term 10 years          
2014 Stock Incentive Plan            
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]            
Common stock reserved for issuance           3,000,000
2018 Stock Incentive Plan            
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]            
Common stock reserved for issuance         4,000,000  
2020 Stock Incentive Plan            
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]            
Common stock reserved for issuance       3,000,000