| In millions, except per share items | Dec-31-22 | Dec-31-21 | Dec-31-20 | Dec-31-19 | Dec-31-18 |
| | 10-K | 10-K | 10-K/A | 10-K | S-1/A |
| Assets | | | | | |
| Current assets: | | | | | |
| Cash and cash equivalents | 52.2 | 101.1 | 92.8 | 15.0 | |
| Marketable securities | 293.6 | 53.2 | 93.0 | | |
| Prepaid expenses and other current assets | 5.6 | 5.3 | 4.9 | 1.4 | |
| Total current assets | 351.4 | 459.6 | 190.7 | 16.9 | |
| Property and equipment, net | 15.3 | 17.6 | | | |
| Restricted cash | 1.7 | 1.7 | | | |
| Other assets | 2.4 | 2.4 | 0.8 | 0.0 | |
| Operating lease right-of-use assets | 34.1 | 38.5 | | | |
| Total assets | 404.9 | 519.8 | 255.6 | 22.3 | |
| |
| Liabilities and Stockholders’ Equity (Deficit) | | | | | |
| Current liabilities: | | | | | |
| Accounts payable | 5.4 | 3.8 | 3.7 | 3.4 | |
| Accrued expenses and other current liabilities | 11.0 | 9.6 | 9.2 | | |
| Operating lease liabilities | 6.0 | 7.0 | | | |
| Deferred revenue | 32.8 | 28.3 | | | |
| Total current liabilities | 55.2 | 48.7 | 18.8 | 12.7 | |
| Operating lease liabilities, net of current portion | 45.5 | 51.3 | | | |
| Deferred revenue, net of current portion | 304.0 | 322.7 | | | |
| Other liabilities | 0.0 | 0.1 | | | |
| Total liabilities | 404.8 | 422.9 | 109.4 | 23.8 | |
| |
| Commitments and contingencies (Note 10) | | | | | |
| Stockholders’ equity (deficit): | | | | | |
| Common stock | 0.0 | 0.0 | 0.0 | | |
| Additional paid-in capital | 377.2 | 361.1 | 309.1 | 6.1 | |
| Accumulated other comprehensive loss | -4.0 | 0.0 | 0.0 | | |
| Accumulated deficit | -373.1 | -264.3 | -162.9 | -94.1 | |
| Total stockholders’ equity (deficit) | 0.1 | 96.9 | 146.2 | -88.0 | |
| Total liabilities and stockholders’ equity (deficit) | 404.9 | 519.8 | 255.6 | 22.3 | |