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Stockholders' Equity - Narrative (Details) - USD ($)
 1 Months Ended 3 Months Ended 12 Months Ended
Nov. 09, 2021
Jan. 25, 2021
Aug. 28, 2020
May 12, 2020
Jun. 30, 2020
May 31, 2018
Mar. 31, 2021
Mar. 31, 2020
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Jan. 01, 2022
May 13, 2016
Class of Stock [Line Items]                          
Convertible preferred stock, shares issued upon conversion, conversion price (in USD per share)                 $ 27.20        
Share-based compensation                 $ 26,336,764 $ 15,647,523 $ 10,901,320    
Employee service share-based compensation, nonvested awards, total compensation cost not yet recognized                 $ 16,500,000 $ 4,400,000      
Employee service share-based compensation, nonvested awards, total compensation cost not yet recognized, period for recognition                 2 years 1 year 4 months 24 days      
Number of options outstanding to purchase common stock (in shares)                 10,488,993 8,906,624      
Aggregate intrinsic value of options outstanding                 $ 3,800,000        
Aggregate intrinsic value for options exercisable                 $ 3,100,000        
Options exercisable, remaining contractual term                 5 years 10 months 24 days        
Number of options expected to vest (in shares)                 10,488,993        
Options, expirations in period, weighted average exercise price (in USD per share)                 $ 4.56 $ 4.44 $ 6.27    
Options, expirations in period (in shares)                 7,000 78,750 324,502    
Options, grants in period, weighted average grant date fair value (in USD per share)                 $ 7.61 $ 6.87 $ 2.19    
Proceeds from stock options exercised                 $ 6,700,000 $ 12,300,000 $ 113,000    
Options, exercises in period, aggregate intrinsic value                 7,000,000 14,200,000 $ 25,000    
Restricted Stock Units (RSUs)                          
Class of Stock [Line Items]                          
Employee service share-based compensation, nonvested awards, total compensation cost not yet recognized                 $ 13,400,000 $ 10,900,000      
Employee service share-based compensation, nonvested awards, total compensation cost not yet recognized, period for recognition                 1 year 9 months 18 days 1 year 10 months 24 days      
Aggregate intrinsic value of unvested                 $ 12,200,000        
Aggregate intrinsic value of vested                 $ 12,700,000        
RSU's expected to vest (in shares)                 2,448,868        
Weighted average grant date fair value (in USD per share)                 $ 10.37 $ 9.12 $ 3.09    
Granted (in shares)                 1,392,124        
Employee                          
Class of Stock [Line Items]                          
Share-based compensation                 $ 25,000,000 $ 14,500,000 $ 9,800,000    
Research and Development Expense                          
Class of Stock [Line Items]                          
Share-based compensation                 13,400,000 8,000,000 5,900,000    
General and Administrative Expense                          
Class of Stock [Line Items]                          
Share-based compensation                 11,600,000 6,500,000 3,900,000    
Non Employee                          
Class of Stock [Line Items]                          
Allocated share-based compensation expense                 $ 1,400,000 $ 1,200,000 $ 970,000    
Number of options outstanding to purchase common stock (in shares)                 632,375        
2016 Incentive Plan                          
Class of Stock [Line Items]                          
Reserved number of shares under the Incentive Plan (in shares)                         20,000,000
Number of potential shares authorized for issuance under a share-based compensation plan (in shares)                         2,000,000
Number of shares available for grants under the Incentive Plan (in shares)                 4,481,745        
Number of shares of vested restricted stock outstanding under the plan (in shares)                 2,448,868        
Number of common stock shares outstanding under the Incentive Plan (in shares)                 8,060,957        
Vesting period of incentive plan                 3 years        
Contractual year term of incentive plan                 10 years        
Award vesting period (in years)                 3 years        
2016 Incentive Plan | Subsequent Event                          
Class of Stock [Line Items]                          
Increase in number of shares authorized (in shares)                       2,000,000  
2016 Incentive Plan | Restricted Stock Units (RSUs)                          
Class of Stock [Line Items]                          
Weighted average grant date fair value (in USD per share)     $ 12.06                    
Granted (in shares)     663,353                    
Grant date fair value     $ 8,000,000                    
2016 Incentive Plan | Restricted Stock Units (RSUs) | Tranche One                          
Class of Stock [Line Items]                          
Vesting percentage     50.00%                    
2016 Incentive Plan | Restricted Stock Units (RSUs) | Tranche Two                          
Class of Stock [Line Items]                          
Vesting period of incentive plan     1 year                    
Vesting percentage     50.00%                    
Award vesting period (in years)     1 year                    
2007 Incentive Plan                          
Class of Stock [Line Items]                          
Number of common stock shares outstanding under the Incentive Plan (in shares)                 2,428,036        
Vesting period of incentive plan                 3 years        
Contractual year term of incentive plan                 10 years        
Award vesting period (in years)                 3 years        
Common stock | Underwritten Public Offering                          
Class of Stock [Line Items]                          
Number of shares issued in transaction (in shares)   20,355,000                      
Sale of stock, price per share (in USD per share)   $ 8.50                      
Commissions and other estimated offering expenses   $ 162,100,000                      
Series C Preferred Stock                          
Class of Stock [Line Items]                          
Conversion of stock, shares converted (in shares)         14                
Convertible preferred stock, shares issued upon conversion (in shares)                 3,309        
Common stock                          
Class of Stock [Line Items]                          
Conversion of stock, shares issued (in shares)         5,147                
Common stock | Sales Agreement                          
Class of Stock [Line Items]                          
Common stock aggregate offering price $ 300,000,000                        
Sales Agents will be entitled to compensation 3.00%                        
Stock sale agreement, aggregate number of shares issued (in shares)                 6,955,341        
Sales made at a weighted average price (in USD per share)                 $ 6.96        
Stock sale agreement, aggregate proceeds from issuance of stock                 $ 47,700,000        
Remaining authorized amount                 $ 251,600,000        
Common stock | Prior Sales Agreement                          
Class of Stock [Line Items]                          
Sale of stock, price per share (in USD per share)             $ 4.92            
Common stock aggregate offering price           $ 100,000,000 $ 250,000,000            
Stock sale agreement, aggregate number of shares issued (in shares)               43,148,952          
Stock sale agreement, aggregate proceeds from issuance of stock               $ 208,200,000          
Remaining authorized amount             $ 0            
Common stock | New Sales Agreement                          
Class of Stock [Line Items]                          
Common stock aggregate offering price       $ 250,000,000                  
Stock sale agreement, aggregate number of shares issued (in shares)                   22,919,934      
Sales made at a weighted average price (in USD per share)                   $ 10.91      
Stock sale agreement, aggregate proceeds from issuance of stock                   $ 246,200,000      
Remaining authorized amount                   $ 0