Quarterly report pursuant to Section 13 or 15(d)

Shareholders' equity (Details)

v3.7.0.1
Shareholders' equity (Details) - USD ($)
3 Months Ended
Mar. 27, 2017
Mar. 31, 2017
Stockholders' equity    
Proceeds from issuance of common stock   $ 61,397,000
Common stock    
Stockholders' equity    
Stock issuance costs   $ 4,544,000
Secondary Public Offering    
Stockholders' equity    
Issuance of shares represented by American Depositary Shares (in ADSs) 15,700,223  
Share price per ADS (in dollars per share) $ 4.20  
Secondary Public Offering | Common stock    
Stockholders' equity    
Issuance of stock (in shares) 94,201,338  
Proceeds from issuance of common stock $ 61,397,000  
Stock issuance costs $ 4,544,000