| 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 |
| | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K |
| Net income | 90.4 | 32.8 | 4.9 | 38.5 | 95.3 | 7.6 | 1.7 |
| Depreciation and amortization [+] | 11.1 | 12.6 | 13.6 | 12.3 | 9.2 | 4.6 | 2.7 |
| Depreciation | 11.1 | 12.6 | 13.6 | 12.3 | 9.2 | 4.6 | 2.7 |
| Stock-based compensation | 33.7 | 35.2 | 29.6 | 23.4 | 20.7 | 0.8 | 0.4 |
| Deferred taxes | 2.7 | -13.1 | 3.1 | -18.4 | -12.3 | -11.2 | |
| Change in working capital [+] | -4.8 | 7.9 | 23.1 | 10.9 | -42.8 | -14.4 | -3.9 |
| Accounts receivable | -20.5 | -7.1 | -4.2 | 21.5 | -66.9 | -23.2 | -6.0 |
| Inventories | 2.8 | -15.3 | 36.7 | -30.6 | -3.8 | -12.9 | 1.1 |
| Other current assets | -1.5 | 6.1 | 6.2 | -6.5 | -10.9 | 1.1 | -2.1 |
| Accounts payable | 15.3 | -0.8 | 1.4 | -2.4 | 23.3 | 11.9 | 1.7 |
| Accrued expenses | -0.2 | 26.8 | -5.5 | 7.0 | 14.4 | 6.7 | 0.2 |
| Deferred revenues | | | | | | 4.1 | 1.3 |
| Other | -0.7 | -1.7 | -11.5 | 21.8 | 1.1 | -2.2 | -0.2 |
| Other operating activities | -2.0 | -2.5 | 8.7 | -4.8 | 32.8 | 35.1 | 12.5 |
| Cash from operations | 131.1 | 72.8 | 83.1 | 61.9 | 102.8 | 22.5 | 13.4 |
| |
| Capital expenditures | -12.9 | -11.8 | -14.7 | -14.1 | -17.3 | -12.1 | -6.5 |
| Purchases of property and equipment | -12.9 | -11.8 | -14.7 | -14.1 | -17.3 | -12.1 | -6.5 |
| Purchases of short-term investments, net | -35.3 | -91.7 | -41.5 | -193.9 | -104.2 | | |
| Purchases of short-term investments | -418.9 | -476.2 | -382.4 | -436.6 | -118.7 | | |
| Sales of short-term investments | 383.7 | 384.5 | 340.9 | 242.7 | 14.5 | | |
| Other cash from investing | 0.0 | 0.0 | -0.1 | 0.1 | -0.1 | 0.0 | 0.0 |
| Cash from investing | -48.2 | -103.6 | -56.2 | -207.9 | -121.5 | -12.1 | -6.5 |
| |
| Issuance of common stock, net | | | -39.7 | | 214.6 | | |
| Option exercises | 2.2 | 6.9 | 5.8 | 5.7 | 2.6 | 0.2 | 0.1 |
| Financing costs | | | | | | 0.0 | 0.0 |
| Other cash from financing | 4.4 | 13.9 | 11.6 | 11.2 | -12.8 | -3.7 | -6.0 |
| Cash from financing | 2.2 | 6.9 | -33.9 | 5.5 | 199.1 | -3.8 | -6.0 |
| |
| Free cash flow | 118.2 | 61.0 | 68.4 | 47.8 | 85.6 | 10.3 | 6.9 |
| Per share (diluted) | $2.73 | $1.43 | $1.63 | $1.15 | $2.89 | $1.24 | $0.93 |
| |
| Cash paid for interest | | | | | | 0.1 | 0.4 |
| Cash paid for income taxes | 3.1 | -0.1 | -5.1 | 1.5 | 3.1 | 7.3 | 4.7 |