| In millions, except per share items | Dec-31-20 | Dec-31-19 | Dec-31-18 | Dec-31-17 | Dec-31-16 | Dec-31-15 | Dec-31-14 | Dec-31-13 |
| | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K |
| Net income | -21.8 | -61.4 | -49.7 | -30.9 | -22.5 | -27.1 | -27.1 | -4.2 |
| Depreciation and amortization [+] | 4.7 | 2.5 | 0.8 | 0.5 | 0.2 | 0.1 | 0.1 | 0.0 |
| Depreciation | 4.7 | 2.5 | 0.8 | 0.5 | 0.2 | 0.1 | 0.1 | 0.0 |
| Asset impairment charges | 3.8 | | | | | | | |
| Stock-based compensation | 7.6 | 7.4 | 6.3 | 5.2 | 3.6 | 4.2 | 4.4 | 0.9 |
| Change in working capital [+] | -4.5 | -4.7 | -2.3 | 3.1 | 9.3 | 11.8 | 12.0 | 1.7 |
| Accounts receivable | 0.4 | 0.0 | -0.9 | | | | | |
| Inventories | 0.2 | -0.6 | -3.6 | | | | | |
| Other current assets | -0.9 | -0.8 | -0.9 | 0.5 | -0.6 | -0.2 | -0.3 | -0.1 |
| Accounts payable | -1.2 | 1.8 | 0.3 | 1.3 | -0.7 | 0.0 | -0.3 | 0.7 |
| Accrued expenses | -3.0 | -5.0 | 2.8 | 1.4 | 1.0 | 0.1 | 1.3 | 1.2 |
| Other | | | | | 9.6 | 11.9 | 11.4 | 0.0 |
| Other operating activities | 0.4 | -0.2 | -0.2 | 0.2 | -9.3 | -11.7 | -11.3 | |
| Cash from operations | -9.9 | -56.3 | -45.0 | -21.9 | -18.8 | -22.8 | -21.9 | -1.6 |
| |
| Capital expenditures [+] | -3.6 | -8.4 | -13.9 | -5.9 | -1.0 | -0.7 | -0.4 | 0.0 |
| Purchases of property and equipment | -3.6 | -8.4 | -13.9 | -5.9 | -1.0 | -0.7 | -0.4 | 0.0 |
| Sales of property and equipment | 0.1 | 0.0 | 0.2 | | | | | |
| Purchases of short-term investments, net | 9.3 | -39.4 | 30.3 | 3.3 | 6.3 | 30.2 | -88.2 | |
| Purchases of short-term investments | -75.7 | -125.0 | -25.1 | -70.1 | -72.0 | -102.2 | -145.2 | |
| Sales of short-term investments | 85.0 | 85.6 | 55.4 | 73.4 | 78.3 | 132.4 | 57.0 | |
| Cash from investing | 5.8 | -47.8 | 16.6 | -2.7 | 5.3 | 29.4 | -88.6 | 0.0 |
| |
| Issuance of common stock, net | 0.2 | 43.1 | 49.2 | 52.2 | | | 58.1 | 54.9 |
| Option exercises | 0.4 | 2.0 | 1.0 | 0.5 | 0.2 | 0.3 | 0.1 | 0.0 |
| Other cash from financing | 0.0 | 22.7 | 1.7 | 1.0 | 0.3 | 0.7 | 0.2 | 11.1 |
| Cash from financing | -0.3 | 63.8 | 49.9 | 52.7 | 0.2 | 0.3 | 58.2 | 66.0 |
| |
| Free cash flow | -13.5 | -64.8 | -59.0 | -27.8 | -19.7 | -23.5 | -22.4 | -1.6 |
| Per share (diluted) | ($0.34) | ($1.68) | ($1.90) | ($1.11) | ($0.99) | ($1.19) | ($1.19) | ($0.43) |