| In millions, except per share items | Jun-30-23 | Mar-31-23 | Dec-31-22 | Sep-30-22 | Jun-30-22 | Mar-31-22 | Dec-31-21 | Sep-30-21 |
| | 10-Q | 10-Q | 10-K | 10-Q | 10-Q | 10-Q | 10-K | 10-Q |
| Operating activities | | | | | | | | |
| Net loss | -49.0 | -47.7 | -51.8 | -48.1 | -43.9 | -40.2 | -194.9 | -194.4 |
| |
| Reconciliation of net loss to net cash used in operating activities: | | | | | | | | |
| Stock-based compensation expense | 4.8 | 4.6 | 4.6 | 4.5 | 4.3 | 4.2 | 3.4 | 2.7 |
| Right-of-use asset - operating lease | 0.3 | 0.1 | | | | | | |
| Other non-cash items | 0.0 | 0.2 | 0.1 | 0.1 | 0.1 | -0.1 | 0.0 | 0.0 |
| Changes in assets and liabilities: | | | | | | | | |
| Prepaid expenses and other assets | -2.0 | -2.6 | -1.6 | 0.7 | -0.7 | -0.5 | 0.1 | 0.0 |
| Lease liability - operating lease | -0.3 | -0.2 | | | -0.7 | -0.7 | | |
| Accounts payable | -0.2 | 0.0 | | 0.2 | 0.4 | -0.9 | -2.0 | -2.8 |
| Accrued expenses | 1.5 | 1.3 | 4.4 | 1.5 | 0.9 | 1.9 | -1.3 | -1.7 |
| Net cash used in operating activities | -44.9 | -44.2 | -43.5 | -39.2 | -36.7 | -34.0 | -30.2 | -31.9 |
| |
| Investing activities | | | | | | | | |
| Purchases of short-term investments | -534.1 | -410.3 | -396.1 | -295.6 | -242.9 | -159.7 | -78.0 | |
| Sales and maturities of short-term investments | 538.0 | 465.3 | 229.0 | 224.7 | 170.0 | 93.6 | 59.0 | |
| Purchases of property and equipment | | -0.1 | -0.1 | -0.1 | 0.0 | | | |
| Net cash provided by (used in) investing activities | 3.8 | 55.0 | -167.1 | -70.9 | -72.9 | -66.1 | -12.6 | |
| |
| Financing activities | | | | | | | | |
| Proceeds from exercise of stock options | 0.4 | 0.1 | 0.1 | 0.1 | | | 0.0 | 0.0 |
| Net cash provided by financing activities | 145.0 | 144.8 | 144.7 | 24.3 | | | 104.3 | 104.3 |
| Net increase (decrease) in cash, cash equivalents and restricted cash | 113.4 | 164.9 | | | -56.5 | -39.7 | | |
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| Supplemental disclosure of non-cash transactions: | | | | | | | | |
| Conversion of Series X Preferred Stock into common stock | | 1.1 | | | | | | |