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Stock-Based Compensation - Additional Information (Detail) - USD ($)
$ / shares in Units, $ in Thousands, shares in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation expense recognized $ 9,061 $ 7,986 $ 7,419
Weighted-average grant date fair value of stock options granted (in dollars per share) $ 8.99 $ 6.00 $ 9.46
Total intrinsic value for options exercised $ 26,800 $ 4,500 $ 1,600
Total unrecognized compensation expense related to non-vested stock options $ 7,700    
Expected weighted-average period of recognition for unrecognized compensation expense 1 year 10 months 20 days    
Maximum contractual term 10 years    
Deferred Bonus Liability $ 900 500 400
Deferred bonus compensation program [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation expense recognized 100 900 700
Recorded as a component of accrued payroll and related expenses 900 600  
Restricted stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation expense recognized $ 4,900 2,400 2,000
Expected weighted-average period of recognition for unrecognized compensation expense 1 year 9 months    
Number of restricted share units issued (in shares) 0.1    
Total unrecognized compensation expense related to non-vested stock awards $ 13,300    
Stock options [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation expense recognized $ 4,100 $ 4,700 $ 4,700