| In millions, except per share items | Jun-30-23 | Mar-31-23 | Jun-30-22 | Mar-31-22 | Dec-31-21 | Sep-30-21 |
| | 10-Q | 10-Q | 10-Q | 10-Q | 8-K | 10-Q |
| Operating expenses: | | | | | | |
| Research and development | | | 116.4 | 80.8 | | |
| General and administrative | | | 54.6 | 51.7 | | |
| Change in fair value of contingent value rights | | | | 17.1 | | |
| Loss from operations | | | -218.2 | -191.1 | | |
| Interest income | | | -4.2 | -2.6 | | |
| Interest expense | | | -3.2 | -1.5 | | |
| Other (expense) income, net | | | 3.6 | -1.9 | | |
| Loss before income taxes | | | -119.1 | -54.4 | | |
| Income tax (benefit) expense | | | 0.2 | 0.2 | | |
| Net loss | | | -220.1 | -196.9 | | |
| |
| Other comprehensive income (loss): | | | | | | |
| Foreign currency translation adjustment | | | -2.3 | -0.1 | | |
| Other comprehensive income (loss) | | | -1.1 | | | |
| Total comprehensive loss | | | -224.5 | -199.0 | | |
| |
| Net loss per ordinary share - basic (in dollars per share) | | | ($1.74) | ($1.70) | | |
| Net loss per ordinary share - diluted (in dollars per share) | | | ($1.74) | ($1.70) | | |
| |
| Weighted average ordinary shares outstanding - basic (in shares) | | | 68.6 | 61.0 | | |
| Weighted average ordinary shares outstanding - diluted (in shares) | | | 68.6 | 61.0 | | |