Stock Based Compensation -Valuation Assumptions Employees (Details) - Employee stock options - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2021 |
Dec. 31, 2020 |
Dec. 31, 2019 |
|
| Weighted-average assumptions used to estimate fair value of share-based awards | |||
| Risk-free interest rate | 0.90% | 0.50% | 1.90% |
| Expected volatility | 86.70% | 82.70% | 82.10% |
| Expected term (in years) | 6 years | 6 years | 6 years |
| Expected dividend yield | 0.00% | 0.00% | 0.00% |
| Unrecognized compensation expense | $ 5.9 | $ 10.4 | $ 13.4 |
| Expected period for recognizing compensation expense | 2 years 8 months 8 days | 2 years 9 months 10 days | 2 years 8 months 15 days |