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Share Based Compensation - Additional Information (Detail) - USD ($)
1 Months Ended 3 Months Ended 6 Months Ended
Apr. 30, 2014
Jun. 30, 2015
Jun. 30, 2014
Jun. 30, 2015
Jun. 30, 2014
Mar. 31, 2015
Sep. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Stock option awards granted   40,000          
Options outstanding, shares   1,306,000   1,306,000   1,335,000  
Stock options vested   140,000          
Aggregate fair value of stock option vested   $ 7,600,000          
Weighted average grant date fair value of stock option awards   $ 73.23 $ 54.01        
Unrecognized share-based compensation expense   $ 48,300,000   $ 48,300,000      
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   130,000   130,000      
2013 Plan              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Share-based compensation expense recognized   $ 4,400,000 $ 3,100,000 $ 8,000,000 $ 4,700,000    
2013 Plan | Class A              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Share-based compensation, stock authorized 1,500,000           600,000
Options outstanding, shares   1,306,250   1,306,250      
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 beginning 2015 5,000            
2013 Plan | Class A | Employees, Officers and Directors              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Stock option awards granted   40,000