Stock-Based Compensation - Restricted Common Stock (Details)
$ / shares in Units, $ in Millions
 1 Months Ended 12 Months Ended
Jun. 21, 2018
USD ($)
Oct. 31, 2018
$ / shares
May 31, 2017
USD ($)
item
$ / shares
shares
Apr. 30, 2017
USD ($)
item
$ / shares
shares
Jan. 31, 2017
USD ($)
$ / shares
shares
Dec. 31, 2020
USD ($)
$ / shares
shares
Dec. 31, 2019
USD ($)
$ / shares
shares
Dec. 31, 2018
USD ($)
Executive officer                
Weighted Average Grant Date Fair Value                
Restricted stock exercise price | $ / shares   $ 16.43   $ 0.18        
Amount recorded in balance sheet due to promissory notes received from sale of common stock       $ 0.0        
Number of promissory notes | item       2        
Unvested restricted common stock                
Number of shares                
Unvested restricted common stock beginning of period | shares           99,314    
Vested | shares           (99,314)    
Unvested restricted common stock end of period | shares             99,314  
Weighted Average Grant Date Fair Value                
Weighted Average Grant Date Fair Value - beginning of the period (in dollars per share) | $ / shares           $ 0.526    
Weighted Average Grant Date Fair Value- vested (in dollars per share) | $ / shares           $ 0.526    
Weighted Average Grant Date Fair Value - End of the period (in dollars per share) | $ / shares             $ 0.526  
The aggregate intrinsic value of restricted stock awards vested           $ 0.8 $ 16.3 $ 34.0
Incremental share based compensation expense               $ 1.5
Unvested restricted common stock | Executive officer                
Number of shares                
Unvested restricted common stock beginning of period | shares     460,000          
Unvested restricted common stock end of period | shares       460,000        
Weighted Average Grant Date Fair Value                
Restricted common stock exercise price | $ / shares       $ 0.19        
Principal amount of promissory note received in exchange for restricted common stock       $ 0.1        
Amount recorded in balance sheet due to promissory notes received from sale of common stock       $ 0.0        
Principal balance of promissory note repaid $ 0.1              
Interest on promissory note repaid 0.1              
Unvested restricted common stock | Board of Directors Chairman                
Number of shares                
Unvested restricted common stock end of period | shares     1,100,000   3,667,014      
Weighted Average Grant Date Fair Value                
Restricted common stock exercise price | $ / shares     $ 1.65   $ 0.19      
Principal amount of promissory note received in exchange for restricted common stock     $ 2.5          
Amount recorded in balance sheet due to promissory notes received from sale of common stock     $ 0.0   $ 0.0      
Number of promissory notes | item     2          
Principal amount of promissory note forgiven 2.5              
Interest on promissory note forgiven $ 0.1              
Restricted Stock Units                
Number of shares                
Unvested restricted common stock beginning of period | shares           277,200    
Forfeited | shares           (25,200)    
Unvested restricted common stock end of period | shares           252,000 277,200  
Weighted Average Grant Date Fair Value                
Weighted Average Grant Date Fair Value - beginning of the period (in dollars per share) | $ / shares           $ 10.660    
Weighted Average Grant Date Fair Value- Forfeited (in dollars per share) | $ / shares           10.660    
Weighted Average Grant Date Fair Value - End of the period (in dollars per share) | $ / shares           $ 10.660 $ 10.660