Balance Sheet Components - Property and Equipment (Details) - USD ($) $ in Thousands |
Dec. 31, 2021 |
Dec. 31, 2020 |
|---|---|---|
| Property and Equipment | ||
| Property and equipment, gross | $ 4,703 | $ 4,698 |
| Less: accumulated depreciation and amortization | (4,252) | (3,792) |
| Property and equipment, net | 451 | 906 |
| Laboratory equipment | ||
| Property and Equipment | ||
| Property and equipment, gross | 2,477 | 2,472 |
| Computer equipment and purchased software | ||
| Property and Equipment | ||
| Property and equipment, gross | 142 | 142 |
| Leasehold improvements | ||
| Property and Equipment | ||
| Property and equipment, gross | $ 2,084 | $ 2,084 |