XML 49 R39.htm IDEA: XBRL DOCUMENT v3.19.1
Share-based compensation - RSU activity (Details) - 2014 Plan - $ / shares
1 Months Ended 3 Months Ended
Mar. 31, 2017
Mar. 31, 2019
Mar. 31, 2017
Non-executive directors      
Other disclosure      
Vesting period (in years)   4 years  
Restricted share units ("RSUs")      
Number of shares      
Non-vested at beginning of year (in shares)   412,321  
Restricted stock granted (in shares)   145,004  
Vested (in shares)   (165,017)  
Forfeited (in shares)   (13,833)  
Non-vested at end of year (in shares)   378,475  
Weighted average grant-date fair value      
Non-vested at beginning of year (in dollars per share)   $ 16.49  
Granted (in dollars per share)   33.62  
Vested (in dollars per share)   12.41  
Forfeited (in dollars per share)   12.25  
Non-vested at end of year (in dollars per share)   24.99  
Restricted share units ("RSUs") | Chief Executive Officer      
Other disclosure      
Vesting period (in years)     2 years
Restricted share units ("RSUs") | Non-executive directors      
Other disclosure      
Vesting period (in years) 1 year    
Restricted share units ("RSUs") | Directors and Officers      
Weighted average grant-date fair value      
Granted (in dollars per share)   $ 4,900,000  
Minimum | Restricted share units ("RSUs")      
Other disclosure      
Vesting period (in years)   1 year  
Maximum | Restricted share units ("RSUs")      
Other disclosure      
Vesting period (in years)   3 years