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Stock Plans - Summary of Stock Option Activity (Detail) - $ / shares
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]      
Outstanding Beginning balance, Shares 1,618,561 1,695,380 1,784,660
Granted, Shares 170,683 138,519 188,407
Exercised, Shares (64,752) (190,743) (277,687)
Expired, Shares (1,109) (1,071)  
Forfeited, Shares (28,708) (23,524)  
Outstanding Ending balance, Shares 1,694,675 1,618,561 1,695,380
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]      
Outstanding Beginning balance, Weighted Average Exercise Price (dollars per share) $ 35.74 $ 34.55 $ 33.05
Granted, Weighted Average Exercise Price (dollars per share) 48.64 51.69 49.03
Exercised, Weighted Average Exercise Price (dollars per share) 38.59 36.31 34.72
Expired, Weighted Average Exercise Price (dollars per share) 44.36 45.68  
Forfeited, Weighted Average Exercise Price (dollars per share) 49.71 38.82  
Outstanding Ending balance, Weighted Average Exercise Price (dollars per share) $ 36.69 $ 35.74 $ 34.55
Exercisable at end of period 1,280,665 1,147,712 1,178,657