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Stockholders' Equity - Assumptions for Valuation of Options Granted under Equity Incentive Plans and Shares Subject to Purchase under Employee Stock Purchase Plan (Detail) (USD $)
3 Months Ended 6 Months Ended
Jun. 30, 2014
Jun. 30, 2013
Jun. 30, 2014
Jun. 30, 2013
Equity Incentive Plans [Member]
       
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Average risk-free interest rate 1.70% 0.71% 1.66% 0.72%
Expected dividend yield 1.80% 2.10% 1.80% 2.10%
Expected life 5 years 1 month 6 days 4 years 10 months 24 days 5 years 1 month 6 days 4 years 9 months 18 days
Expected volatility 30.00% 36.00% 30.00% 37.00%
Weighted average fair value $ 8.67 $ 9.27 $ 8.76 $ 9.05
Employee Stock Purchase Plan [Member]
       
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Average risk-free interest rate 0.08% 0.11% 0.08% 0.11%
Expected dividend yield 1.80% 2.10% 1.80% 2.10%
Expected life 6 months 6 months 6 months 6 months
Expected volatility 25.00% 25.00% 25.00% 25.00%
Weighted average fair value $ 7.81 $ 5.97 $ 7.81 $ 5.97