| In millions, except per share items | Dec-31-21 | Dec-31-20 | Dec-31-19 | Dec-31-18 | Dec-31-17 | Dec-31-16 |
| | 10-K | 10-K | 10-K | 10-K | 10-K | S-1/A |
| CASH FLOWS FROM OPERATING ACTIVITIES: | | | | | | |
| Net loss | -26.0 | -15.2 | -12.5 | -11.2 | 4.3 | |
| Adjustments to reconcile net loss to net cash used in operating activities: | | | | | | |
| Depreciation and amortization | 0.1 | 0.1 | 0.1 | 0.0 | | |
| Stock-based compensation | 8.2 | 3.3 | 2.0 | 2.3 | 0.3 | |
| Provision for losses on accounts receivable | 0.1 | | | | | |
| Changes in operating assets and liabilities: | | | | | | |
| Accounts receivable | -0.1 | 0.0 | 0.1 | -0.1 | 0.0 | |
| Other current assets | 0.2 | 0.1 | -0.3 | 0.0 | -0.1 | |
| Accounts payable | 2.5 | 0.4 | 1.4 | -0.4 | 1.3 | |
| Accrued liabilities | -1.5 | 3.6 | 0.1 | 0.7 | 0.0 | |
| Insurance reserve | 0.2 | 0.8 | 1.0 | 0.3 | | |
| Net cash used in operating activities | -17.7 | -7.8 | -8.1 | -6.5 | -2.5 | |
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| CASH FLOWS FROM INVESTING ACTIVITIES: | | | | | | |
| Net cash used in investing activities | -0.4 | 0.0 | 0.0 | -0.2 | -0.1 | |
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| CASH FLOWS FROM FINANCING ACTIVITIES: | | | | | | |
| Proceeds from sale of common stock | 29.7 | | 12.1 | 12.6 | 2.2 | |
| Offering costs associated with sale of common stock | -2.1 | 0.0 | | | | |
| Proceeds from exercise of stock options | 0.2 | 0.1 | 0.1 | | | |
| Proceeds from exercise of warrants | 0.1 | | 0.9 | | | |
| Notes payable - related party | | 2.0 | | | 0.1 | |
| Net cash provided by financing activities | 27.9 | 2.1 | 12.0 | 13.3 | 2.4 | |
| Increase (decrease) in cash, cash equivalents and restricted cash | 9.8 | -5.7 | | | | |
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| Cash, cash equivalents and restricted cash | | | | | | |
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| Reconciliation of cash, cash equivalents and restricted cash to the condensed consolidated balance sheets | | | | | | |
| Cash and cash equivalents | | | | | | |
| Restricted cash | | | | | | |
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| Supplemental disclosures of cash flow information: | | | | | | |
| Interest expense | | | | | | |
| Income taxes | 0.0 | 0.0 | 0.0 | | | |
| Non-cash investing and financing activities: | | | | | | |