Quarterly report pursuant to Section 13 or 15(d)

Share-Based Compensation - Additional Information (Details)

v3.19.2
Share-Based Compensation - Additional Information (Details) - USD ($)
$ / shares in Units, $ in Thousands
6 Months Ended
Dec. 05, 2018
Oct. 14, 2016
Oct. 14, 2015
Jun. 30, 2019
Jun. 30, 2018
Dec. 31, 2018
Mar. 14, 2018
May 18, 2017
Nov. 18, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Ordinary shares, shares issued       14,407,202   14,352,046      
Share options awarded       512,178          
Restricted Ordinary Shares                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Shares issued in the period     413,110            
Percentage of remaining restricted ordinary shares vest on monthly basis   0.0278%              
Grant date fair value       $ 3.14   $ 3.14     $ 3.14
Expense recognized       $ 167 $ 165        
Unamortized stock compensation expense       $ 93 $ 428        
Stock-based compensation expense, expected weighted average period for recognition       3 months 14 days 1 year 3 months 14 days        
Number of shares, outstanding       34,162   86,068      
Restricted Ordinary Shares | Tranche One                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Percentage of awards vested   25.00%              
Employee Stock Options                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Expense recognized       $ 655 $ 189        
Unvested employee options outstanding       925,549 663,916        
Unamortized compensation expense share options       $ 4,107 $ 3,549        
Vesting period       3 years 25 days 3 years 8 months 15 days        
Restricted Share Units (RSUs)                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Grant date fair value       $ 7.01   $ 13.00      
Expense recognized       $ 201 $ 50        
Unamortized stock compensation expense       $ 210 $ 431        
Stock-based compensation expense, expected weighted average period for recognition       11 months 15 days 10 months 24 days        
Number of Shares, Granted       31,367 36,924        
Number of shares, awarded       31,367 36,924        
Number of shares, outstanding       31,367   36,924      
Restricted Share Units (RSUs) | Director                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Vesting period       1 year          
Performance RSUs                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Grant date fair value       $ 8.21          
Expense recognized       $ 90          
Unamortized stock compensation expense       $ 320          
Stock-based compensation expense, expected weighted average period for recognition       1 year 3 months 25 days          
Number of Shares, Granted       50,000 0        
Number of shares, awarded       50,000 0        
Number of shares, outstanding       50,000 0        
Restricted Ordinary Shares, Options and Restricted Share Units and Performance Restricted Share Units                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Vesting period       2 years 9 months 29 days 3 years 2 months 15 days        
Unamortized compensation expense       $ 4,730 $ 4,408        
2018 Plan                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Number of shares authorized             1,018,459   223,424
Number of ordinary shares available for issuance               443,029 219,605
Increase in number of ordinary shares available to be granted, percentage 4.00%                
Ordinary shares, shares issued           574,081      
2018 Plan | Employee Stock Options                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Share options awarded       512,178 447,984