| In millions, except per share items | Dec-31-21 | Dec-31-20 | Dec-31-19 | Dec-31-18 | Dec-31-17 | Dec-31-16 | Dec-31-15 | Dec-31-14 |
| | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | S-1/A |
| ASSETS | | | | | | | | |
| Current assets: | | | | | | | | |
| Cash and cash equivalents | 22.8 | 3.0 | 14.1 | 21.2 | 21.1 | 73.0 | 3.4 | |
| Restricted cash | 0.1 | 0.1 | | | | | | |
| Accounts and other receivables | 2.8 | 2.6 | | | | | | |
| Inventory | 3.0 | 2.2 | 1.9 | 1.6 | 1.4 | 0.8 | 0.4 | |
| Prepaid expenses and other current assets | 1.8 | 1.2 | 2.0 | 2.5 | 1.7 | 1.2 | 0.3 | |
| Total current assets | 30.3 | 8.9 | 18.2 | 28.6 | 51.8 | 78.1 | 13.8 | |
| Property and equipment, net | 1.5 | 0.6 | 1.1 | 1.7 | 1.3 | 0.7 | 0.4 | |
| Operating lease right-of-use assets | 0.3 | 0.5 | | | | | | |
| Other assets | 1.5 | 0.0 | | | | | | |
| Total assets | 54.3 | 37.1 | 20.4 | 30.4 | 53.1 | 78.8 | 14.2 | |
| |
| LIABILITIES AND STOCKHOLDERS' EQUITY | | | | | | | | |
| Current liabilities: | | | | | | | | |
| Accounts payable | 3.5 | 3.7 | 0.6 | 1.2 | 1.3 | 0.6 | | |
| Accrued and other liabilities | 3.2 | 3.6 | | | | | | |
| Warranty liability, current | 0.4 | 0.4 | | | | | | |
| Operating lease liabilities, current | 0.3 | 0.3 | | | | | | |
| Total current liabilities | 7.3 | 11.6 | 4.0 | 17.2 | 10.0 | 4.6 | 5.6 | |
| Total liabilities | 8.2 | 22.6 | 4.5 | 17.3 | 18.0 | 14.5 | 14.7 | |
| |
| Commitments and contingencies (Note 13) | | | | | | | | |
| Stockholders' equity: | | | | | | | | |
| Preferred stock | | | | | | | | |
| Common stock | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | |
| Additional paid-in capital | 622.9 | 529.4 | 188.3 | 161.9 | 146.5 | 140.9 | 1.0 | |
| Accumulated deficit | -576.8 | -514.8 | -172.4 | -148.8 | -111.4 | -76.6 | -56.1 | |
| Accumulated other comprehensive loss | -0.1 | -0.1 | | | 0.0 | 0.0 | | |
| Total stockholders' equity | 46.1 | 14.5 | 15.8 | 13.1 | 35.1 | 64.3 | -55.1 | |
| Total liabilities and stockholders' equity | 54.3 | 37.1 | 20.4 | 30.4 | 53.1 | 78.8 | 14.2 | |