Share-based Compensation - Option Activity (Details) - USD ($)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Number of Options        
Beginning balance (in shares) 38,011,964 34,811,741    
Ending balance (in shares) 39,614,883 38,011,964 34,811,741  
Aggregate Intrinsic Value        
Aggregate intrinsic value, outstanding $ 466,460,320 $ 51,303,638 $ 20,683,833  
Liability award – share options        
Number of Options        
Beginning balance (in shares) 0 1,150,784 1,150,784  
Granted (in shares)   0 0  
Repurchased (in shares)   (1,100,000)    
Forfeited (in shares)   0 0  
Reclassified to equity classified award (in shares)   (50,784)    
Ending balance (in shares) 0 0 1,150,784 1,150,784
Weighted Average Exercise Price        
Beginning balance (in dollars per share) $ 0 $ (0.10) $ (0.10)  
Granted (in dollars per share)   0 0  
Forfeited (in dollars per share)   0 0  
Repurchased (in dollars per share)   0.10    
Reclassified to equity classified award (in dollars per share)   0.10    
Ending balance (in dollars per share) $ 0 $ 0 $ 0.10 $ 0.10
Weighted Average Remaining Contractual Life        
Weighted-average remaining contractual term, outstanding     5 years 11 months 19 days 6 years 11 months 19 days
Weighted average remaining contractual term, repurchased (in years)   5 years 8 months 1 day    
Weighted average remaining contractual term, reclassified to equity classified award (in years)   6 years 9 months 21 days    
Aggregate Intrinsic Value        
Aggregate intrinsic value, repurchased   $ 818,845    
Aggregate intrinsic value, outstanding     $ 689,258 $ 286,842
Aggregate intrinsic value, reclassified   $ 37,804    
Weighted Average Grant Date Fair Value        
Options outstanding, weighted average grant date fair value (in dollars per share)     $ 0.07 $ 0.07
Options repurchased, weighted average grant date fair value (in dollars per share)   $ 0.07    
Options reclassified to equity classified award, weighted average grant date fair value (in dollars per share)   $ 0.10    
Equity award – share options        
Number of Options        
Beginning balance (in shares) 38,011,964 33,660,957 20,412,350  
Granted (in shares) 9,941,500 5,087,648 14,689,473  
Exercised (in shares) (7,632,431)      
Forfeited (in shares) (706,150) (787,425) (1,440,866)  
Reclassified from liability award (in shares)   50,784    
Ending balance (in shares) 39,614,883 38,011,964 33,660,957 20,412,350
Vested and expected to vest, end of period (in shares) 34,982,436      
Exercisable, end of period (in shares) 34,982,436      
Weighted Average Exercise Price        
Beginning balance (in dollars per share) $ (0.12) $ (0.11) $ (0.10)  
Granted (in dollars per share) 0.19 0.24 0.12  
Forfeited (in dollars per share) 0.16 0.13 0.10  
Reclassified from liability award (in dollars per share)   0.10    
Ending balance (in dollars per share) 0.17 $ 0.12 $ 0.11 $ 0.10
Vested and expected to vest, end of period (in dollars per share) 0.11      
Exercisable, end of period (in dollars per share) $ 0.11      
Weighted Average Remaining Contractual Life        
Weighted-average remaining contractual term, outstanding 8 years 2 months 23 days 7 years 2 months 19 days 7 years 10 months 28 days 7 years 10 months 2 days
Weighted average remaining contractual term, vested and expected to vest 5 years 10 months 6 days      
Weighted average remaining contractual term, exercisable 5 years 10 months 6 days      
Aggregate Intrinsic Value        
Aggregate intrinsic value, outstanding $ 466,460,320 $ 51,303,638 $ 19,994,575 $ 5,087,933
Aggregate intrinsic value, vested and expected to vest 339,504,760      
Aggregate intrinsic value, exercisable $ 339,504,760      
Weighted Average Grant Date Fair Value        
Options outstanding, weighted average grant date fair value (in dollars per share) $ 1.08 $ 0.31 $ 0.23 $ 0.12
Options granted, weighted-average grant-date fair value per share (in dollars per share) 3.16 $ 0.86 $ 0.37  
Options vested and expected to vest, weighted average grant date fair value (in dollars per share) 1.20      
Options exercisable, weighted average grant date fair value (in dollars per share) $ 1.20