| 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 | -131.8 | -55.4 | -55.5 | -38.0 | 17.9 | -40.0 | -47.3 | -46.9 |
| Depreciation and amortization [+] | | | | 0.5 | 0.4 | 0.3 | 0.5 | 0.5 |
| Depreciation | | | | 0.5 | 0.4 | 0.3 | 0.5 | 0.5 |
| Stock-based compensation | | | | 10.8 | 8.7 | 8.5 | 9.0 | 8.2 |
| Change in working capital [+] | 23.4 | 0.6 | 5.4 | 52.1 | -20.8 | -26.4 | -2.5 | 1.7 |
| Accounts receivable | -0.3 | 0.0 | -0.2 | | | | | 0.4 |
| Other current assets | | | | -0.7 | -0.7 | 0.0 | 0.2 | -0.4 |
| Accounts payable | | | | -0.4 | 0.7 | 0.0 | -0.1 | -0.2 |
| Other | 23.7 | 0.6 | 5.6 | 53.2 | -20.8 | -26.4 | -2.7 | 1.9 |
| Other operating activities | 32.7 | -26.4 | -20.0 | -9.0 | -1.3 | 96.6 | 1.0 | 2.1 |
| Cash from operations | -75.6 | -81.1 | -70.1 | 16.4 | 4.9 | 39.1 | -39.3 | -34.3 |
| |
| Capital expenditures | 19.0 | 15.4 | 0.8 | -0.8 | -0.7 | -0.3 | -0.2 | -0.4 |
| Purchases of property and equipment | 19.0 | 15.4 | 0.8 | -0.8 | -0.7 | -0.3 | -0.2 | -0.4 |
| Purchases of short-term investments, net | 726.1 | 624.4 | 412.2 | -52.2 | 16.3 | -48.5 | 34.1 | 38.7 |
| Purchases of short-term investments | 307.4 | 445.7 | 212.0 | -192.5 | -133.8 | -136.2 | -24.4 | -100.8 |
| Sales of short-term investments | 418.7 | 178.7 | 200.2 | 140.3 | 150.2 | 87.8 | 58.5 | 139.5 |
| Other cash from investing | -652.9 | -922.2 | -425.5 | | | | | |
| Cash from investing | 92.2 | -282.4 | -12.5 | -53.1 | 15.6 | -48.8 | 33.9 | 38.3 |
| |
| Issuance of common stock, net | | 325.7 | 73.3 | | | 7.0 | | |
| Option exercises | 7.4 | 30.3 | 22.9 | 10.5 | 3.3 | 1.8 | 2.2 | 2.1 |
| Other cash from financing | 8.5 | 61.3 | 44.4 | 35.2 | 10.8 | 3.6 | 4.4 | 3.9 |
| Cash from financing | 1.1 | 356.6 | 94.8 | 24.7 | 7.5 | 8.8 | 2.2 | 1.8 |
| |
| Free cash flow | -56.6 | -65.7 | -69.3 | 15.6 | 4.2 | 38.8 | -39.5 | -34.7 |
| Per share (diluted) | ($0.81) | ($1.00) | ($1.22) | $0.31 | $0.08 | $0.84 | ($0.90) | ($0.80) |
| |
| Cash paid for interest | 2.0 | 1.9 | 1.7 | 0.7 | | | | 0.1 |