Quarterly report pursuant to Section 13 or 15(d)

Shareholders' Equity - Reconciliation of Beginning and Ending Balances in Shareholders' Equity (Details)

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Shareholders' Equity - Reconciliation of Beginning and Ending Balances in Shareholders' Equity (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Dec. 31, 2017
Class Of Stock [Line Items]          
Shareholders' equity, Beginning Balance     $ 39,494 $ 22,668 $ 22,668
Conversion of preferred shares to ordinary shares     74    
Share-based compensation expense     404 180  
Issuance of warrants     139    
Net loss $ (15,747) $ (6,280) (27,893) (12,117) (29,406)
Shareholders' equity, Ending Balance $ 118,530 $ 56,571 118,530 56,571 $ 39,494
Series B Convertible Preferred Shares          
Class Of Stock [Line Items]          
Issuance of shares     32,159 $ 45,840  
Ordinary Shares          
Class Of Stock [Line Items]          
Issuance of shares     $ 74,153