Income Taxes - U S federal statutory income tax rate (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2021 |
Dec. 31, 2020 |
Dec. 31, 2019 |
|
| Income Taxes | |||
| Income tax benefits - operating losses incurred | $ 0.0 | $ 0.0 | $ 0.0 |
| Federal statutory income tax rate | (21.00%) | (21.00%) | |
| State taxes, net of federal benefit | (6.20%) | (6.20%) | |
| Federal and state research and development tax credits | (6.40%) | (5.90%) | |
| Stock-based compensation expense | (1.60%) | 0.40% | |
| Section 162(m) compensation deduction limitation | 1.60% | ||
| Other | (0.40%) | 0.50% | |
| Increase in deferred tax asset valuation allowance | 34.00% | 32.20% | |