| In millions, except per share items | Dec-31-22 | Dec-31-21 | Dec-31-20 | Dec-31-19 | Dec-31-18 | Dec-31-17 | Dec-31-16 | Dec-31-15 |
| | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K |
| Operating Activities | | | | | | | | |
| Net loss | -30.6 | -27.0 | -20.4 | -16.1 | -18.0 | -14.8 | -11.9 | -9.5 |
| |
| Adjustments to reconcile net loss to net cash used in operating activities: | | | | | | | | |
| Depreciation and amortization | 0.9 | 0.9 | 0.7 | 0.7 | 0.6 | 0.5 | 0.3 | 0.2 |
| Amortization of operating lease right-of-use assets | 0.3 | 0.2 | 0.3 | 0.2 | | | | |
| Stock-based compensation | 3.1 | 7.6 | 1.4 | 1.5 | 2.6 | 2.4 | 1.7 | 1.5 |
| Gain on change in fair value of warrant liability | | | | | | | | -0.3 |
| Changes in operating assets and liabilities: | | | | | | | | |
| Prepaid expenses | 0.4 | -0.3 | 0.0 | 0.0 | 0.0 | -0.1 | 0.0 | 0.0 |
| Accounts receivable | -0.1 | 0.0 | 0.0 | | | | | |
| Other current assets | 0.4 | -0.2 | -0.3 | -0.1 | 0.0 | 0.0 | 0.0 | -0.1 |
| Deferred revenue, current and non-current | 10.0 | 0.0 | | | | | | |
| Accounts payable and accrued liabilities | 0.5 | 0.5 | 2.1 | 1.1 | 0.1 | -0.3 | 1.1 | -0.1 |
| Management and directors' fees payable | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | | | |
| Net Cash Used In Operating Activities | -15.3 | -20.9 | -16.5 | -12.7 | -14.7 | -12.2 | -8.9 | -8.5 |
| |
| Investing Activities | | | | | | | | |
| Purchases of property and equipment | -1.6 | -1.0 | -1.9 | -0.5 | -0.3 | -1.4 | -0.4 | -0.1 |
| Net Cash Used In Investing Activities | -1.6 | -1.0 | -1.6 | -0.5 | -0.3 | -1.4 | -0.4 | -0.1 |
| |
| Financing Activities | | | | | | | | |
| Net proceeds from issuances of common stock | 6.7 | 23.2 | 21.2 | 16.6 | 17.2 | 1.0 | 25.3 | 12.5 |
| Tax withholdings paid related to stock-based compensation | | | -0.2 | | | | | |
| Common stock repurchased | | | -0.1 | | | | | |
| Payments on long-term debt | | | | | -0.4 | | | |
| Net Cash Provided By (Used In) Financing Activities | 6.9 | 22.9 | 20.6 | 16.9 | 18.0 | 2.0 | 25.2 | 12.4 |
| Net change in cash and cash equivalents | -9.7 | 1.1 | | | | | | |
| |
| Supplemental Disclosures of Cash Flow Information | | | | | | | | |
| Interest paid | 0.2 | 0.2 | 0.1 | 0.1 | 0.1 | 0.1 | 0.0 | 0.0 |
| |
| Non-Cash Financing Activities | | | | | | | | |
| Offering costs from issuance of common stock | | | 1.3 | | | | | |
| Fair value of warrants issued in connection with public offering | | | | | | | | |