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Stock Plans - Weighted Average Assumptions and Fair Value of Stock Option Grants (Detail) - $ / shares
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]      
Fair value per option (dollars per share) $ 15.63 $ 17.26 $ 14.17
Risk-free interest rate 1.80% 2.10% 1.20%
Expected dividend yield 2.30% 2.40% 2.80%
Expected volatility 39.00% 41.00% 39.00%
Expected life (years) 6 years 8 months 16 days 6 years 7 months 6 days 6 years 1 month 6 days