XML 67 R57.htm IDEA: XBRL DOCUMENT v3.10.0.1
Share Capital - Changes in Number of Shares of Class A Stock Outstanding (Details) - Class A Stock - shares
3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]        
Class A Stock outstanding, beginning of period 13,156,353 13,132,775 13,139,203 13,261,095
Issued pursuant to shared-based compensation plans 21,578 19,883 38,728 198,903
Repurchased and canceled pursuant to the stock buy-back 0 143,010 0 450,350
Class A Stock outstanding, end of period 13,177,931 13,009,648 13,177,931 13,009,648