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Share-based Compensation - Additional Information (Detail) - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Dec. 31, 2018
Stock Option Awards      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock option awards granted 30,000    
Options outstanding, shares 1,460,000   1,480,000
2013 Equity Plan | Stock Option Awards      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock options vested 132,000    
Aggregate fair value of stock option vested $ 7.6    
Weighted average grant date fair value of stock option awards $ 54.85 $ 52.44  
Share-based compensation expense recognized $ 3.0 $ 4.7  
Unrecognized share-based compensation expense $ 30.9    
Unrecognized compensation expense expected to be recognized 2 years 10 months 24 days    
2013 Equity Plan | Other Stock-based Awards      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Unrecognized compensation expense expected to be recognized 3 years 2 months 12 days    
Other stock-based awards granted 0    
Unrecognized share-based compensation expense $ 0.5    
2013 Equity Plan | Class A | Stock Option Awards      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock option awards granted 30,000    
Options outstanding, shares 1,459,983    
2013 Equity Plan | Class A | Board of Directors      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation, stock authorized 2,300,000    
2013 Equity Plan | Class A | Employees, Officers, and Directors | Stock Option Awards      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares of class A common stock reserved and available for future issuance 573,750