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Assumptions of Weighted Average for ESPP Purchases Utilizing Black-Scholes Model (Detail) - Employee Stock Purchase Plan - $ / shares
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Dividend yield 0.50% 0.60% 0.60%
Risk-free interest rate 0.45% 0.14% 0.08%
Expected life in years 6 months 6 months 6 months
Expected volatility 21.00% 17.00% 18.00%
Fair value $ 42.71 $ 33.45 $ 27.73