Annual report pursuant to Section 13 and 15(d)

Stock-Based Compensation - Fair value assumptions (Details)

v3.19.1
Stock-Based Compensation - Fair value assumptions (Details) - $ / shares
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Feb. 28, 2018
Oct. 31, 2017
Sep. 30, 2017
Stock-Based Compensation          
Authorized shares 3,444,894        
Fair value of grants per share     $ 6.88 $ 4.82 $ 4.82
Options          
Stock-Based Compensation          
Terms of award ten        
Vesting period 4 years        
Weighted-average grant-date fair value of options (in dollars per share) $ 7.64 $ 0.41      
Expected dividend yield (as a percent) 0.00%        
Options | Employees          
Stock-Based Compensation          
Expected stock price volatility, minimum (as a percent) 77.12%        
Expected stock price volatility, maximum (as a percent) 81.49%        
Risk-free rate of interest, minimum (as a percent) 2.68%        
Risk-free rate of interest, maximum (as a percent) 3.12%        
Options | Employees | Minimum          
Stock-Based Compensation          
Exercise price per share (in dollars per share) $ 0.41        
Fair value of grants per share $ 3.41        
Expected Term (years) 4 years 8 months 12 days        
Options | Employees | Maximum          
Stock-Based Compensation          
Exercise price per share (in dollars per share) $ 11.00        
Fair value of grants per share $ 10.82        
Expected Term (years) 7 years        
Options | Non-Employees          
Stock-Based Compensation          
Expected stock price volatility, minimum (as a percent) 76.03%        
Expected stock price volatility, maximum (as a percent) 82.91%        
Risk-free rate of interest, minimum (as a percent) 2.43%        
Risk-free rate of interest, maximum (as a percent) 2.68%        
Options | Non-Employees | Minimum          
Stock-Based Compensation          
Exercise price per share (in dollars per share) $ 0.41        
Fair value of grants per share $ 2.37        
Expected Term (years) 3 months 18 days        
Options | Non-Employees | Maximum          
Stock-Based Compensation          
Exercise price per share (in dollars per share) $ 11.00        
Fair value of grants per share $ 7.16        
Expected Term (years) 9 years 9 months 18 days