v3.19.2
Stock incentive plans - Plans (Details) - shares
Jun. 30, 2019
Dec. 31, 2018
Stock options    
Stock incentive plans    
Number of options outstanding 289,000 304,000
Stock options | 2011 Plan    
Stock incentive plans    
Number of options outstanding 279,000  
RSUs | 2011 Plan    
Stock incentive plans    
RSUs outstanding 855,000