| 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/A | 10-K | 10-K | 10-K | 10-K |
| Net income | -51.8 | -219.3 | -37.3 | -26.3 | -25.9 | -27.4 | -36.1 | -32.6 |
| Depreciation and amortization | | | | | 0.1 | 0.3 | 0.4 | 0.2 |
| Stock-based compensation | 4.6 | 3.4 | 1.4 | | 1.8 | 2.0 | 2.2 | 1.7 |
| Change in working capital [+] | 2.1 | -3.2 | 3.2 | -1.8 | 0.8 | -1.9 | 0.3 | 0.7 |
| Other current assets | -1.6 | 0.1 | 1.3 | -1.3 | -0.2 | -0.1 | -0.2 | -0.5 |
| Accounts payable | -0.8 | -2.0 | 0.3 | -0.2 | 0.7 | -0.6 | 0.1 | 0.2 |
| Accrued expenses | 4.4 | -1.3 | 1.6 | -0.2 | 0.4 | -1.2 | 0.4 | 1.0 |
| Other | | | | -0.1 | 0.0 | 0.0 | 0.0 | 0.0 |
| Other operating activities | 1.7 | 189.0 | 0.2 | 1.5 | -0.3 | 0.2 | 0.4 | 0.3 |
| Cash from operations | -43.5 | -30.2 | -32.5 | -26.6 | -23.5 | -26.8 | -32.9 | -29.8 |
| |
| Capital expenditures [+] | -0.1 | 0.0 | 0.0 | 0.0 | 0.0 | -0.1 | -0.5 | -0.4 |
| Purchases of property and equipment | -0.1 | 0.0 | 0.0 | 0.0 | | -0.1 | -0.5 | -0.4 |
| Sales of property and equipment | | | | | 0.4 | 0.0 | 0.1 | |
| Purchases of short-term investments, net | -167.0 | -19.0 | 6.3 | -4.1 | -22.3 | 14.9 | -15.1 | |
| Purchases of short-term investments | -396.1 | -78.0 | -62.8 | -155.2 | -70.4 | | -45.5 | |
| Sales of short-term investments | 229.0 | 59.0 | 69.1 | 151.1 | 48.1 | 14.9 | 30.5 | |
| Other cash from investing | | 6.5 | | | | | | |
| Cash from investing | -167.1 | -12.6 | 6.3 | -4.1 | -21.9 | 14.9 | -15.5 | -0.4 |
| |
| Issuance of common stock, net | 107.6 | 104.3 | 24.6 | 18.5 | 38.9 | | 10.6 | 61.7 |
| Option exercises | 0.1 | 0.0 | 0.0 | 0.1 | 0.0 | 0.0 | 0.5 | 0.1 |
| Financing costs | | | | | | | | 0.0 |
| Other cash from financing | 37.2 | 0.0 | 16.3 | 7.2 | 5.4 | 4.7 | -0.9 | 16.7 |
| Cash from financing | 144.7 | 104.3 | 40.9 | 25.6 | 44.3 | 4.7 | 9.2 | 78.3 |
| |
| Free cash flow | -43.6 | -30.2 | -32.5 | -26.6 | -23.5 | -26.9 | -33.3 | -30.2 |
| Per share (diluted) | ($2.98) | ($3.38) | ($10.63) | ($2.37) | ($4.64) | ($12.40) | ($2.05) | ($3.76) |
| |
| Cash paid for interest | | | | | 0.1 | 0.3 | 0.6 | 0.7 |