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Stock Option Activity (Detail) - USD ($)
$ / shares in Units, $ in Thousands
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Option shares      
Options Outstanding at beginning of period 326,022    
Granted 0    
Exercised 4,323 3,854 5,850
Canceled 85,295    
Options Outstanding at end of period 236,404 326,022  
Options Exercisable at end of period 236,404    
Weighted average exercise price per share      
Options Outstanding at beginning of period $ 20.54    
Granted 0    
Exercised 12.64    
Canceled 21.98    
Options Outstanding at end of period 20.17 $ 20.54  
Options Exercisable at end of period $ 20.17    
Weighted average remaining contractual term (years)      
Options Outstanding at end of period 5 years 6 months    
Options Exercisable at end of period 5 years 6 months    
Aggregate Intrinsic Value      
Options Outstanding at end of period $ 707    
Options Exercisable at end of period $ 707