XML 68 R57.htm IDEA: XBRL DOCUMENT v3.10.0.1
Capital Stock (Details)
 1 Months Ended 3 Months Ended 9 Months Ended
Nov. 30, 2016
USD ($)
Sep. 30, 2018
USD ($)
director
common_share
shares
Sep. 30, 2018
USD ($)
director
common_share
$ / shares
Sep. 30, 2017
USD ($)
$ / shares
Class of Stock [Line Items]        
Classes of common shares | common_share   2 2  
Accelerated share repurchase program, agreement to repurchase $ 25,000,000      
Accelerated share repurchases, payment   $ 25,000,000 $ 25,000,000  
Stock Repurchased and Retired During Period, Shares | shares   1,300,000.0    
Accelerated Share Repurchase Program, Amount Of Shares Repurchased, Percent   80.00%    
Stock repurchased during period, value     $ 30,270,000 $ 11,705,000
Minimum        
Class of Stock [Line Items]        
Minimum number of directors up for election to entitle shareholders to vote | director   0.3333 0.3333  
Maximum        
Class of Stock [Line Items]        
Minimum number of directors up for election to entitle shareholders to vote | director   3 3  
Common stock, Class A        
Class of Stock [Line Items]        
Stock repurchase program, authorized amount $ 100,000,000      
Stock repurchased during period, value     $ 5,300,000 $ 11,700,000
Stock repurchase program, remaining authorized amount   $ 52,300,000 $ 52,300,000  
Common stock, Class A | Minimum        
Class of Stock [Line Items]        
Stock repurchased during period (in dollars per share) | $ / shares     $ 13.29 $ 16.82
Common stock, Class A | Maximum        
Class of Stock [Line Items]        
Stock repurchased during period (in dollars per share) | $ / shares     $ 16.86 $ 23.01