Convertible Preferred Stock (Details) - USD ($)
$ / shares in Units, $ in Thousands
1 Months Ended 6 Months Ended
Jul. 20, 2018
Jul. 31, 2018
Feb. 28, 2018
Jun. 30, 2018
Jun. 30, 2019
Dec. 31, 2018
Convertible Preferred Stock            
Proceeds from issuance of convertible preferred stock       $ 100,986    
Payments of initial public offering costs       $ 715    
Preferred stock outstanding         0 0
Series C convertible preferred stock            
Convertible Preferred Stock            
Preferred stock issued     7,912,432      
Convertible preferred stock issue price (dollars per share)     $ 12.79      
Proceeds from issuance of convertible preferred stock     $ 101,200      
Payments of initial public offering costs     $ 200      
Common stock            
Convertible Preferred Stock            
Number of common stock issued on conversion 51,845,438 51,845,438