Annual report pursuant to Section 13 and 15(d)

Stock Option and Purchase Plans - Summary of Weighted Average Exercise Prices and Contractual Lives for Outstanding and Exercisable Stock Options (Detail)

v3.8.0.1
Stock Option and Purchase Plans - Summary of Weighted Average Exercise Prices and Contractual Lives for Outstanding and Exercisable Stock Options (Detail) - $ / shares
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Outstanding        
Shares (in shares) 1,310,090 1,338,273 1,444,954 1,686,178
Weighted average remaining life (in years) 4 years 4 months 24 days      
Weighted average exercise price (in usd per share) $ 16.85 $ 14.85 $ 12.61 $ 9.43
Exercisable        
Shares (in shares) 1,088,970 1,091,561 1,167,040  
Weighted average remaining life (in years) 3 years 7 months 6 days      
Weighted average exercise price (in usd per share) $ 12.84 $ 11.03 $ 9.20  
$ 3.07 - $ 3.67        
Share-based Compensation Arrangement by Share-based Payment Award        
Exercise price, lower range (in usd per share) 3.07      
Exercise price, upper range (in usd per share) $ 3.67      
Outstanding        
Shares (in shares) 470,757      
Weighted average remaining life (in years) 1 year 6 months      
Weighted average exercise price (in usd per share) $ 3.29      
Exercisable        
Shares (in shares) 470,757      
Weighted average remaining life (in years) 1 year 6 months      
Weighted average exercise price (in usd per share) $ 3.29      
$ 6.35 - $ 6.35        
Share-based Compensation Arrangement by Share-based Payment Award        
Exercise price, lower range (in usd per share) 6.35      
Exercise price, upper range (in usd per share) $ 6.35      
Outstanding        
Shares (in shares) 15,055      
Weighted average remaining life (in years) 2 months 12 days      
Weighted average exercise price (in usd per share) $ 6.35      
Exercisable        
Shares (in shares) 15,055      
Weighted average remaining life (in years) 2 months 12 days      
Weighted average exercise price (in usd per share) $ 6.35      
$ 8.83 - $15.68        
Share-based Compensation Arrangement by Share-based Payment Award        
Exercise price, lower range (in usd per share) 8.83      
Exercise price, upper range (in usd per share) $ 15.68      
Outstanding        
Shares (in shares) 374,619      
Weighted average remaining life (in years) 4 years      
Weighted average exercise price (in usd per share) $ 11.52      
Exercisable        
Shares (in shares) 374,619      
Weighted average remaining life (in years) 4 years      
Weighted average exercise price (in usd per share) $ 11.52      
$ 26.09 - $41.19        
Share-based Compensation Arrangement by Share-based Payment Award        
Exercise price, lower range (in usd per share) 26.09      
Exercise price, upper range (in usd per share) $ 41.19      
Outstanding        
Shares (in shares) 429,819      
Weighted average remaining life (in years) 8 years      
Weighted average exercise price (in usd per share) $ 35.06      
Exercisable        
Shares (in shares) 208,699      
Weighted average remaining life (in years) 7 years 4 months 24 days      
Weighted average exercise price (in usd per share) $ 33.41      
$ 52.77 - $52.77        
Share-based Compensation Arrangement by Share-based Payment Award        
Exercise price, lower range (in usd per share) 52.77      
Exercise price, upper range (in usd per share) $ 52.77      
Outstanding        
Shares (in shares) 19,840      
Weighted average remaining life (in years) 7 years 2 months 12 days      
Weighted average exercise price (in usd per share) $ 52.77      
Exercisable        
Shares (in shares) 19,840      
Weighted average remaining life (in years) 7 years 2 months 12 days      
Weighted average exercise price (in usd per share) $ 52.77