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Share-based Compensation - Additional Information (Detail) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Jun. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Stock option awards granted 0        
Options outstanding, shares 942,000   942,000   949,000
Stock options vested 15,000        
Aggregate fair value of stock option vested $ 1,200,000        
Unrecognized share-based compensation expense 20,800,000   $ 20,800,000    
Unrecognized compensation expense expected to be recognized     2 years 1 month 7 days    
Increase in additional paid-in capital       $ 1,200,000  
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  
Payments related to tax withholding for net-share settlement of share-based award     0 3,739,000  
2013 Equity Plan          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Share-based compensation expense recognized $ 3,700,000 $ 3,300,000 10,600,000 8,400,000  
Payments related to tax withholding for net-share settlement of share-based award     0 3,700,000  
Adjustment to Additional paid in capital related to tax withholding for net-share settlement of share-based award     $ 0 $ 3,700,000  
2013 Equity Plan | Class A          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Share-based compensation, stock authorized 1,700,000   1,700,000    
2013 Equity Plan | Class A | Employees, Officers, and Directors          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Stock option awards granted 0 0      
Options outstanding, shares 941,633   941,633    
Remaining shares of class A common stock authorized for future issuance 535,000   535,000