Stock-Based Compensation - Schedule of Fair Value of Stock Purchase Rights Granted Under 2018 Employee Stock Purchase Plan (Detail) - 2018 Employee Stock Purchase Plan [Member] |
12 Months Ended | |
|---|---|---|
Dec. 31, 2021 |
Dec. 31, 2020 |
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||
| Expected dividend yield | 0.00% | 0.00% |
| Expected term | 6 months 25 days | 5 months 23 days |
| Risk-free interest rate | 0.10% | 0.80% |
| Expected volatility | 88.00% | 81.00% |