Annual report pursuant to Section 13 and 15(d)

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

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Stockholders' equity - Underwritten public offering and Registered direct offering (Details) - USD ($)
 12 Months Ended
Aug. 10, 2020
Jun. 04, 2020
Jan. 24, 2020
Dec. 31, 2021
Dec. 31, 2020
Stockholders' equity          
Proceeds from issuance of common stock from offerings, net of commissions and issuance costs       $ 2,529,000 $ 334,388,000
Issue of shares under At The Market sales agreement, net of commission and expenses       2,529,000  
Remaining amount under the Sales Agreement       $ 197,360,000  
Common stock          
Stockholders' equity          
Issuance of common stock (in shares)       3,069,330  
Issue of shares under At The Market sales agreement, net of commission and expenses       $ 4,000  
Issue of shares under At The Market sales agreement, net of commission and expenses, shares       3,069,330  
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    
Proceeds from issuance of common stock from offerings, net of commissions and issuance costs       $ 2,529,000  
Issue of shares under At The Market sales agreement, net of commission and expenses, shares       511,555  
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    
Maximum | American Depository Shares (ADSs)          
Stockholders' equity          
Issue of shares under At The Market sales agreement, net of commission and expenses $ 200,000,000