Quarterly report pursuant to Section 13 or 15(d)

Share-Based Compensation - Additional Information (Details)

v3.19.1
Share-Based Compensation - Additional Information (Details) - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended
Dec. 05, 2018
Oct. 14, 2016
Oct. 14, 2015
Mar. 31, 2019
Dec. 31, 2018
Mar. 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       14,367,441 14,352,046        
Share options granted       442,500          
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       $ 85 $ 82        
Unamortized stock compensation expense       $ 175 $ 510        
Stock-based compensation expense, expected weighted average period for recognition       6 months 14 days 1 year 6 months 14 days        
Number of shares, outstanding       60,250 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 Share Options                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Expense recognized       $ 307   $ 67      
Unvested employee options outstanding       984,913   221,553      
Unamortized compensation expense share options       $ 4,168   $ 1,132      
Vesting period       3 years 3 months 18 days   3 years 3 months 7 days      
Employees and Directors                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Share options granted       442,500          
Restricted Share Units (RSUs)                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Grant date fair value       $ 13.00 $ 13.00        
Expense recognized       $ 119          
Unamortized stock compensation expense       $ 72          
Stock-based compensation expense, expected weighted average period for recognition       1 month 24 days          
Number of shares, awarded       0   0      
Number of shares, outstanding       36,924 36,924 0      
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       $ 29          
Unamortized stock compensation expense       $ 381          
Stock-based compensation expense, expected weighted average period for recognition       1 year 6 months 21 days          
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 11 months 23 days   2 years 3 months 25 days      
Unamortized compensation expense       $ 4,796   $ 1,642      
Two Thousand Fifteen Equity Incentive Plan                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Number of shares authorized                 223,424
Number of ordinary shares available for issuance               443,029 219,605
2018 Plan                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Number of shares authorized             1,018,459    
Increase in number of ordinary shares available to be granted, percentage 4.00%                
Ordinary shares, shares issued         574,081        
2018 Plan | Employee Share Options                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Share options granted           74,152