In millions, except per share items | Jun-30-23 | Dec-31-22 | Jun-30-22 | Mar-31-22 | Dec-31-21 | Sep-30-21 | Jun-30-21 | Dec-31-20 |
| 10-Q | | 10-Q | 10-Q | 10-K | 10-Q | 10-Q | 10-K |
Assets | | | | | | | | |
Current assets: | | | | | | | | |
Cash and cash equivalents | 217.3 | | 141.2 | 119.8 | 171.4 | 184.2 | 399.4 | 102.0 |
Marketable securities | 514.1 | | 256.4 | 260.8 | 236.7 | 243.4 | | 126.2 |
Accounts receivable | | | 1.0 | 2.0 | 2.3 | 2.6 | 1.3 | 7.3 |
Prepaid expenses and other current assets | 11.3 | | 8.0 | 6.8 | 7.9 | 5.2 | 3.9 | 3.9 |
Total current assets | 742.6 | | 406.6 | 389.5 | 418.3 | 435.4 | 436.8 | 239.4 |
Operating lease right-of-use assets | 2.8 | | 4.2 | 4.5 | 4.8 | | | |
Property and equipment, net | 2.5 | | 2.4 | 2.4 | 2.6 | 2.6 | 2.3 | 2.6 |
Restricted cash | 0.6 | | 0.6 | 0.6 | 0.6 | 0.6 | 0.3 | 0.3 |
Other assets | 0.2 | | 0.2 | 0.2 | 0.0 | 0.0 | 0.0 | 0.1 |
Total assets | 748.7 | | 413.9 | 397.1 | 426.3 | 438.6 | 439.5 | 242.4 |
|
Liabilities | | | | | | | | |
Current liabilities: | | | | | | | | |
Accounts payable | 3.7 | | 3.9 | 3.5 | 4.8 | 3.2 | 5.3 | 3.8 |
Accrued expenses | 14.1 | | 11.3 | 10.0 | 12.8 | 8.4 | 16.7 | 10.2 |
Deferred revenue, current portion | | | 4.5 | 30.3 | 20.6 | 30.1 | 21.8 | 25.3 |
Total current liabilities | 17.8 | | 19.7 | 43.8 | 38.3 | 41.8 | 34.9 | 39.4 |
|
Long-term liabilities: | | | | | | | | |
Operating lease liability, net of current portion | 1.6 | | 3.1 | 3.5 | 3.8 | | | |
Total liabilities | 19.4 | | 25.9 | 83.7 | 89.6 | 88.4 | 91.6 | 97.2 |
|
Commitments and contingencies (Note 10) | | | | | | | | |
Stockholders’ Equity | | | | | | | | |
Common shares | 0.0 | | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
Additional paid‑in capital | 1,103.5 | | 633.1 | 584.7 | 575.2 | 566.9 | 539.5 | 287.7 |
Accumulated deficit | -372.2 | | -242.7 | -269.5 | -238.1 | -216.7 | -191.6 | -142.5 |
Accumulated other comprehensive loss | -1.9 | | -2.4 | -1.8 | -0.5 | -0.1 | 0.0 | 0.0 |
Total stockholders’ equity | 729.4 | | 388.0 | 313.4 | 336.7 | 350.2 | 347.9 | 145.2 |
Total liabilities and stockholders’ equity | 748.7 | | 413.9 | 397.1 | 426.3 | 438.6 | 439.5 | 242.4 |