| 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 | 10-K |
| Net income | 19.7 | -39.4 | -116.5 | -199.5 | -114.8 | -78.2 | -41.9 | -21.3 |
| Depreciation and amortization [+] | 1.7 | 2.8 | 4.6 | 4.4 | 1.3 | 0.7 | 0.3 | 0.0 |
| Depreciation | 0.1 | 2.2 | 4.6 | 4.4 | 1.3 | 0.7 | 0.3 | 0.0 |
| Amortization of intangible assets | 1.6 | 0.6 | | | | | | |
| Asset impairment charges | 0.9 | 2.5 | | | | | | |
| Stock-based compensation | 4.5 | 6.2 | 23.7 | 35.2 | 21.8 | 14.5 | 11.6 | 9.0 |
| Change in working capital [+] | -7.8 | -14.3 | 98.3 | 0.5 | 6.2 | 4.3 | 3.4 | 7.2 |
| Restricted cash | | | | | | | -0.2 | |
| Accounts receivable | -2.8 | -1.7 | -1.6 | -1.4 | | | | |
| Inventories | -1.1 | -1.5 | -0.2 | -2.0 | | | | |
| Other current assets | -2.4 | 2.3 | 0.6 | -2.0 | -1.6 | -0.7 | 0.8 | -0.1 |
| Accrued expenses | -0.7 | -11.4 | 0.4 | 5.5 | -0.2 | 0.2 | -0.2 | 0.7 |
| Other | -0.8 | -2.0 | 99.0 | 0.4 | 8.1 | 4.7 | 3.0 | 6.5 |
| Other operating activities | 9.4 | 4.6 | -95.0 | 7.0 | 0.4 | -0.1 | 1.5 | -7.8 |
| Cash from operations | 28.2 | -37.6 | -85.0 | -152.4 | -85.1 | -58.7 | -25.2 | -12.9 |
| |
| Capital expenditures [+] | 0.0 | 0.0 | -0.7 | -2.3 | -9.2 | -2.2 | -1.8 | -0.3 |
| Purchases of property and equipment | 0.0 | | -0.7 | -2.3 | -9.2 | -2.2 | -1.8 | -0.3 |
| Sales of property and equipment | | 3.1 | | | | | | |
| Purchases of short-term investments, net | | -0.5 | | | | | | |
| Purchases of short-term investments | | -3.0 | | | | | | |
| Sales of short-term investments | | 2.5 | | | | | | |
| Other cash from investing | | -33.5 | | | | | | |
| Cash from investing | 0.0 | -30.9 | -0.7 | -2.3 | -9.2 | -2.2 | -1.8 | -0.3 |
| |
| Issuance of common stock, net | -3.2 | 0.6 | 0.0 | 109.8 | 117.5 | | 104.6 | 53.1 |
| Option exercises | | | | 1.9 | 2.7 | 0.1 | 0.3 | |
| Other cash from financing | 0.4 | 0.5 | 0.8 | 128.5 | 5.4 | 0.3 | 0.6 | |
| Cash from financing | -2.8 | 1.1 | 0.9 | 236.4 | 120.2 | 0.1 | 104.9 | 53.1 |
| |
| Free cash flow | 28.2 | -37.6 | -85.6 | -154.7 | -94.3 | -60.9 | -27.0 | -13.1 |
| Per share (diluted) | $0.83 | ($1.38) | ($3.16) | ($6.09) | ($4.44) | ($3.54) | ($1.73) | ($1.23) |
| |