v3.19.2
Shareholders' equity (deficit) - Share-based compensation -Summary (Details) - shares
6 Months Ended
Jun. 30, 2019
May 08, 2019
May 07, 2019
Dec. 31, 2018
Jun. 30, 2018
Dec. 31, 2017
Share-based compensation            
Options outstanding 2,440,629     2,295,045 1,801,235 968,782
2011 Plan            
Share-based compensation            
Total number of shares available for awards under the plan     2,787,063      
Options outstanding 2,393,631          
2011 Plan | Options | Share-based Compensation Award, Tranche One            
Share-based compensation            
Percentage of shares to vest 25.00%          
2011 Plan | Options | Share-based Compensation Award, Tranche Two            
Share-based compensation            
Percentage of shares to vest 2.0833%          
2019 Plan            
Share-based compensation            
Total number of shares available for awards under the plan   4,710,564        
Number of new shares available for awards under the plan   1,923,501        
Percentage of shares reserved for future issuance   4.00%        
2019 Plan | Options            
Share-based compensation            
Total number of shares available for awards under the plan 2,322,573          
Aggregate number of shares granted 46,998          
Available for future grants 2,275,575