v3.19.3.a.u2
Equity Incentive Plans - Schedule of Fair Value of Stock Option Award and ESPP on Grant Date (Detail) - $ / shares
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Stock options [Member]      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Risk-free interest rate 2.40% 2.50% 1.80%
Expected term (in years) 4 years 6 months 4 years 8 months 12 days 5 years 1 month 6 days
Expected volatility 48.00% 42.00% 42.00%
Dividend yield 0.00% 0.00% 0.00%
Grant-date fair value per share $ 111.59 $ 121.92 $ 122.25
Employee stock purchase plan [Member]      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Risk-free interest rate 2.20% 2.00% 1.10%
Expected term (in years) 6 months 6 months 6 months
Expected volatility 53.00% 43.00% 35.00%
Dividend yield 0.00% 0.00% 0.00%
Grant-date fair value per share $ 78.25 $ 84.37 $ 75.05