Quarterly report pursuant to Section 13 or 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 ($)
3 Months Ended 6 Months Ended
Aug. 10, 2021
Jun. 30, 2021
Jun. 30, 2020
Mar. 31, 2020
Jun. 30, 2021
Jun. 30, 2020
Stockholders' equity            
Issue of shares under At The Market sales agreement, net of commission and expenses   $ 2,519,000        
Remaining amount under the Sales Agreement         $ 197,359,541  
Proceeds from issuance of common stock from offerings, net of commissions and issuance costs         $ 2,519,000 $ 334,388,000
Common stock            
Stockholders' equity            
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        
Issuance of common stock (in shares)   3,069,330 141,450,000 144,900,000    
American Depository Shares (ADSs)            
Stockholders' equity            
Issue of shares under At The Market sales agreement, net of commission and expenses, shares   511,555        
Proceeds from issuance of common stock from offerings, net of commissions and issuance costs   $ 2,519,000        
Maximum | American Depository Shares (ADSs)            
Stockholders' equity            
Issue of shares under At The Market sales agreement, net of commission and expenses $ 200,000,000