Income Taxes - Valuation allowance for deferred tax assets (Details) - USD ($) $ in Thousands |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2021 |
Dec. 31, 2020 |
Dec. 31, 2019 |
|
| Income Taxes | |||
| Valuation allowance as of beginning of year | $ 139,877 | $ 85,884 | $ 33,666 |
| Increases recorded to income tax provision | 66,830 | 53,993 | 52,218 |
| Valuation allowance as of end of year | $ 206,707 | $ 139,877 | $ 85,884 |