v3.19.1
Stock incentive plans - Plans (Details) - shares
Mar. 31, 2019
Dec. 31, 2018
Stock options    
Stock incentive plans    
Number of options outstanding 300,000 304,000
Stock options | 2011 Plan    
Stock incentive plans    
Number of options outstanding 290,000  
RSUs | 2011 Plan    
Stock incentive plans    
RSUs outstanding 970,000