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Stock-based Compensation - Schedule of ESPP Purchase Rights and Underlying Weighted Average Assumptions (Detail) - ESPP [Member] - $ / shares
6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Weighted average fair value per share $ 12.03 $ 10.39
Minimum [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected volatility 24.00% 22.00%
Risk-free interest rate 0.70% 0.50%
Expected term (in years) 6 months 6 months
Maximum [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected volatility 28.00% 25.00%
Risk-free interest rate 1.20% 0.80%
Expected term (in years) 2 years 2 years