| 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 |
| Net income | -35.7 | -28.3 | -19.2 | -44.6 | -27.2 | -51.0 | -82.3 | -73.2 |
| Depreciation and amortization [+] | 0.6 | 0.4 | 0.3 | 0.1 | 0.0 | 1.7 | 2.2 | 1.3 |
| Depreciation | 0.6 | 0.4 | 0.3 | 0.1 | 0.0 | 1.7 | 2.2 | 1.3 |
| Asset impairment charges | | | | | | 0.4 | 2.1 | |
| Stock-based compensation | 1.6 | 1.1 | 0.5 | 4.3 | 1.4 | 6.9 | 9.2 | 19.3 |
| Change in working capital [+] | 11.0 | 9.6 | 6.0 | -0.9 | 1.0 | -4.7 | 4.6 | -0.5 |
| Other current assets | 0.9 | -0.2 | 0.4 | -0.7 | -2.5 | 0.9 | 0.9 | -1.1 |
| Accounts payable | 0.0 | -0.2 | -0.6 | -0.5 | 0.3 | 0.1 | -1.2 | -0.2 |
| Accrued expenses | 1.7 | 0.7 | -0.2 | 0.3 | 3.2 | -5.8 | 4.8 | 0.8 |
| Other | 8.3 | 9.2 | 6.4 | | | | | |
| Other operating activities | -8.5 | -8.7 | -6.6 | -0.2 | 1.1 | 1.2 | 2.4 | 2.8 |
| Cash from operations | -31.1 | -26.0 | -19.0 | -41.2 | -23.6 | -45.6 | -61.7 | -50.3 |
| |
| Capital expenditures | -0.6 | -0.1 | -0.1 | -0.4 | 0.0 | -0.2 | -2.6 | -5.2 |
| Purchases of property and equipment | -0.6 | -0.1 | -0.1 | -0.4 | 0.0 | -0.2 | -2.6 | -5.2 |
| Acquisitions | | | | | -0.5 | | | |
| Purchases of short-term investments, net | | | | 4.4 | 2.5 | 18.9 | -10.7 | -41.7 |
| Purchases of short-term investments | | | | | | -68.9 | -82.7 | -95.2 |
| Sales of short-term investments | | | | 4.4 | 2.5 | 87.8 | 72.0 | 53.5 |
| Other cash from investing | | 0.0 | 0.0 | | | -1.5 | 21.5 | 8.6 |
| Cash from investing | -0.6 | -0.1 | 0.0 | 4.0 | 1.9 | 17.3 | 8.3 | -38.3 |
| |
| Issuance of common stock, net | 8.9 | 33.4 | | 26.7 | 38.8 | | 53.9 | 124.1 |
| Option exercises | | 0.1 | 0.1 | | | | | |
| Financing costs | | -0.1 | | | -1.4 | | | |
| Other cash from financing | 2.5 | 25.7 | 34.7 | 0.3 | 37.6 | | 0.2 | 1.3 |
| Cash from financing | 11.4 | 59.1 | 34.6 | 26.9 | 77.7 | 0.0 | 54.1 | 125.4 |
| |
| Free cash flow | -31.6 | -26.1 | -19.1 | -41.6 | -23.7 | -45.7 | -64.3 | -55.5 |
| Per share (diluted) | ($2.74) | ($6.88) | ($40.73) | ($3.04) | ($15.31) | ($1.28) | ($2.00) | ($2.05) |
| |
| Cash paid for interest | 1.5 | 1.0 | | | | | | |
| Cash paid for income taxes | 0.0 | | | | 0.0 | | | |