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Share-based Compensation - Additional Information (Detail) - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock option awards granted 475,000    
Options outstanding, shares 1,463,000   992,000
Stock options vested 55,000    
Aggregate fair value of stock option vested $ 4.0    
Weighted average grant date fair value of stock option awards $ 52.44 $ 77.31  
Unrecognized share-based compensation expense $ 40.0    
Unrecognized compensation expense expected to be recognized 3 years 3 months 18 days    
2013 Equity Plan      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation expense recognized $ 4.7 $ 3.1  
2013 Equity Plan | Class A      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation, stock authorized 1,700,000    
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      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock option awards granted 475,000    
Options outstanding, shares 1,462,883    
Remaining shares of class A common stock authorized for future issuance 613,750    
Remaining shares of class A common stock authorized for future issuance, pending stockholder approval 600,000