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Fair Value-Based Measurements and Weighted-Average Assumptions (Detail) (USD $)
9 Months Ended 3 Months Ended
Sep. 30, 2014
Sep. 30, 2013
Sep. 30, 2014
Employee Stock Purchase Plan
Sep. 30, 2013
Employee Stock Purchase Plan
Sep. 30, 2014
Stock Options
Sep. 30, 2013
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Weighted-average fair value $ 1.52 $ 2.43 $ 0.74 $ 0.93 $ 1.01 $ 1.15
Risk-free interest rate 1.80% 1.10% 0.20% 0.20% 1.90% 1.90%
Expected life (in years) 5 years 10 months 24 days 5 years 10 months 24 days 1 year 1 month 6 days 1 year 3 months 18 days 5 years 9 months 18 days 6 years
Volatility 1.40% 1.40% 0.90% 0.80% 0.80% 1.50%