| In millions, except per share items | Jun-30-23 | Mar-31-23 | Sep-30-22 | Jun-30-22 | Mar-31-22 | Dec-31-21 | Sep-30-21 | Jun-30-21 |
| | 10-Q | 10-Q | 10-Q | 10-Q | 10-Q | 10-K | 10-Q | 10-Q |
| Revenues: | | | | | | | | |
| Total revenues | | | | | | | | |
| Operating expenses: | | | | | | | | |
| Cost of license fees and collaboration revenue | | | | 0.6 | 0.1 | | 0.1 | |
| Research and development | | | 40.6 | 39.9 | 37.5 | 41.7 | 41.3 | 39.0 |
| General and administrative | | | 37.1 | 31.8 | 28.2 | 25.4 | 22.5 | 18.0 |
| Total operating expenses | | | 63.5 | 57.5 | 37.0 | | 16.9 | |
| Loss from operations before other income (expense) and income taxes | | | -62.1 | -54.9 | -42.4 | -12.2 | -9.2 | -3.6 |
| |
| Other income (expense): | | | | | | | | |
| Interest income | | | 1.4 | 0.3 | | | 0.0 | 0.0 |
| Interest expense | | | -1.5 | -0.9 | -0.3 | | | |
| Other (expense) income, net | | | 0.1 | 0.1 | 0.0 | -0.1 | -0.1 | -0.1 |
| Total other income (expense), net | | | -1.2 | -1.9 | -2.3 | -1.6 | -1.3 | -1.0 |
| Provision for income taxes | | | 0.1 | | 0.4 | 0.1 | 0.0 | -0.3 |
| Net (loss) income | | | -63.3 | -56.5 | -44.4 | -13.8 | -10.4 | -4.9 |
| |
| Other comprehensive loss: | | | | | | | | |
| Comprehensive loss | | | -63.4 | -56.5 | -44.4 | -13.8 | -10.4 | -4.9 |
| |
| Earnings Per Share [Abstract] | | | | | | | | |
| Net loss per share, basic (usd per share) | | | ($2.78) | ($2.70) | ($2.15) | ($1.68) | $0.45 | ($2.50) |
| Net loss per share, diluted (usd per share) | | | ($2.78) | ($2.70) | ($2.17) | ($0.72) | $1.41 | ($1.54) |
| |
| Weighted Average Number of Shares Outstanding, Diluted [Abstract] | | | | | | | | |
| Weighted-average shares outstanding, basic (shares) | | | 23.1 | 21.6 | 20.6 | 20.5 | 16.9 | 12.5 |
| Weighted-average shares outstanding, diluted (shares) | | | 23.1 | 21.6 | 21.0 | 21.2 | 17.7 | 13.2 |