Annual report pursuant to Section 13 and 15(d)

Stockholders' equity - Underwritten public offering and Registered direct offering (Details)

v3.20.4
Stockholders' equity - Underwritten public offering and Registered direct offering (Details) - USD ($)
12 Months Ended
Jun. 04, 2020
Jan. 24, 2020
Sep. 07, 2018
Dec. 31, 2018
Stockholders' equity        
Proceeds from issuance of common stock       $ 99,653,000
Common stock        
Stockholders' equity        
Issuance of common stock (in shares)       60,000,000
Matrix Capital Management Company L P, New Enterprise Associates 16, L.P. New Enterprise Associates 14, L.P. and Syncona Portfolio Limited        
Stockholders' equity        
Share price per ADS (in dollars per share)     $ 10.00  
Issuance of shares represented by American Depositary Shares (in ADSs)     10,000,000  
Matrix Capital Management Company L P, New Enterprise Associates 16, L.P. New Enterprise Associates 14, L.P. and Syncona Portfolio Limited | Common stock        
Stockholders' equity        
Issuance of common stock (in shares)     60,000,000  
Proceeds from issuance of common stock     $ 99,653,000  
Stock offering expenses     $ 347,000  
American Depository Shares (ADSs)        
Stockholders' equity        
Issuance of common stock (in shares) 3,075,000 21,000,000    
Net proceeds $ 243,834,000 $ 90,554,000    
American Depository Shares (ADSs) | Underwritten public offering        
Stockholders' equity        
Issuance of common stock (in shares) 20,500,000      
American Depository Shares (ADSs) | Over-Allotment Option        
Stockholders' equity        
Issuance of common stock (in shares)   3,150,000