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Share Based Compensation - Additional Information (Detail) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2015
Sep. 30, 2014
Sep. 30, 2015
Sep. 30, 2014
Oct. 29, 2015
Jun. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Stock option awards granted 130,000 0        
Options outstanding, shares 1,436,000   1,436,000     1,306,000
Stock options vested 125,000          
Aggregate fair value of stock option vested $ 5,300,000          
Weighted average grant date fair value of stock option awards $ 82.89          
Unrecognized share-based compensation expense $ 54,500,000   $ 54,500,000      
Unrecognized compensation expense expected to be recognized     3 years      
Tax benefit realized from exercise of stock options     $ 1,000,000 $ 0.0    
Class A            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Remaining shares of class A common stock authorized for future issuance 0   0      
2013 Plan            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Share-based compensation expense recognized $ 4,500,000 $ 3,900,000 $ 12,500,000 $ 8,600,000    
2013 Plan | Class A            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Share-based compensation, stock authorized 1,500,000   1,500,000   1,700,000  
Options outstanding, shares 1,436,250   1,436,250      
2013 Plan | Class A | Officers and Employees            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Stock option awards granted 130,000          
2013 Plan | Class A | Non Employee Directors            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Number of automatic annual stock option grants authorized to each of the Company's non-employee directors began 2015     5,000