| In millions, except per share items | Dec-31-22 | Dec-31-21 | Dec-31-20 | Dec-31-19 | Dec-05-19 | Dec-31-18 | Dec-05-18 | Dec-31-17 |
| | 10-K | 10-K | 10-K | 10-K | 8-K | 10-K | 8-K | 10-K |
| Operating expenses | | | | | | | | |
| Research and development | 49.8 | 35.1 | 6.4 | 8.1 | | 10.3 | | 15.6 |
| General and administrative | 35.1 | 22.9 | 8.0 | 6.1 | 6.1 | 5.8 | 5.8 | 9.4 |
| Total operating expenses | 84.9 | 58.0 | 21.3 | 14.2 | 14.2 | 16.1 | 16.1 | 25.0 |
| Loss from operations | -84.9 | -58.0 | -21.3 | -14.2 | -14.2 | -16.1 | -16.1 | -25.0 |
| Other income (expense), net | 3.5 | -0.4 | -0.5 | -6.1 | 0.8 | -2.1 | 0.0 | -1.5 |
| Net loss | -81.4 | -58.4 | -21.8 | -20.2 | -20.2 | -18.2 | -18.2 | -26.4 |
| |
| Other comprehensive income (loss) | | | | | | | | |
| Foreign currency translation adjustment | 0.0 | | | | | | | |
| Unrealized gain (loss) on marketable securities | 0.0 | | | | | | | |
| Comprehensive loss | -81.3 | -58.4 | -21.8 | -20.2 | | -18.2 | | |
| |
| Shares used in calculating net loss per common share - basic (in shares) | 214.6 | 195.0 | 112.2 | 13.9 | 13.9 | 5.0 | 5.0 | 22.7 |
| Shares used in calculating net loss per common share - diluted (in shares) | 214.6 | 195.0 | 112.2 | 13.9 | 13.9 | 5.0 | 5.0 | 22.7 |
| |
| Net loss per share of common stock - basic (in USD per share) | ($0.38) | ($0.30) | ($0.31) | ($1.46) | ($1.46) | ($3.67) | ($3.67) | ($0.99) |
| Net loss per share of common stock - diluted (in USD per share) | ($0.38) | ($0.30) | ($0.31) | ($1.46) | ($1.46) | ($3.67) | ($3.67) | ($0.99) |