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Stock-Based Compensation - Summarized Information for the Plans (Detail) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]      
Outstanding, Beginning Balance (in shares) 495,704    
Granted (in shares) 0    
Exercised (in shares) (210,125)    
Expired (in shares) 0    
Canceled (in shares) 0    
Outstanding, Ending Balance (in shares) 285,579 495,704  
Exercisable, Ending Balance (in shares) 285,579    
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]      
Weighted Average Exercise Price, Outstanding, Beginning Balance (in dollars per share) $ 21.24    
Granted (in dollars per share) 0.00    
Exercised (in dollars per share) 20.10    
Expired (in dollars per share) 0.00    
Canceled (in dollars per share) 0.00    
Weighted Average Exercise Price, Outstanding, Ending Balance (in dollars per share) 22.08 $ 21.24  
Weighted Average Exercise Price, Exercisable (in dollars per share) $ 22.08    
Aggregate Intrinsic Value, Outstanding $ 3,790    
Aggregate Intrinsic Value, Exercisable $ 3,790    
Granted (in dollars per share) $ 0.00 $ 0.00  
Aggregate intrinsic value of options exercised $ 4,194 $ 2,640 $ 20,100
Weighted average grant-date fair value of shares vested $ 1,400 $ 2,633 $ 4,602
Stock options      
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]      
Granted (in dollars per share)     $ 0.00
Restricted stock units      
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]      
Granted (in dollars per share) $ 38.33 $ 36.02 $ 36.35
Weighted average grant-date fair value of shares vested $ 5,627 $ 3,195 $ 2,629