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Share-based Compensation - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Stock option awards granted 175,000 45,000 380,000  
Options outstanding, shares 992,000 886,000 1,323,000 1,201,000
Expected dividend yield 0.00% 0.00% 0.00%  
Stock options vested 215,000 222,500 283,750  
Aggregate fair value of stock option vested $ 13,000,000 $ 13,700,000 $ 14,200,000  
Weighted average grant date fair value of stock option awards $ 68.67 $ 75.54 $ 73.86  
Unrecognized share-based compensation expense $ 19,800,000      
Unrecognized compensation expense expected to be recognized 2 years 3 months 18 days      
Increase in additional paid-in capital   $ 1,244,000 $ 1,096,000  
Deferred tax assets wrote off due to vested stock options not exercisable $ 0 1,700,000    
Decrease in additional-paid in capital 0 1,700,000 0  
Payments related to tax withholding for net-share settlement of share-based award 0 3,739,000 0  
Class A        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Increase in additional paid-in capital   0 0  
2013 Equity Plan        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based compensation expense recognized 14,300,000 11,800,000 17,300,000  
Payments related to tax withholding for net-share settlement of share-based award 0 3,700,000 0  
Adjustment to Additional paid in capital related to tax withholding for net-share settlement of share-based award $ 0 $ 3,700,000 $ 0  
2013 Equity Plan | Class A        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based compensation, stock authorized 1,700,000      
Share-based compensation award expiration period 10 years      
Stock option awards, vesting period 4 years      
2013 Equity Plan | Class A | Employees, Officers, and Directors        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Stock option awards granted 175,000      
Options outstanding, shares 991,633      
Remaining shares of class A common stock authorized for future issuance 485,000