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 |