| 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 | 178.7 | 59.2 | 168.6 | 150.6 | 75.2 | -4.2 | 36.9 | 44.2 |
| Depreciation and amortization | 26.0 | 27.9 | 24.1 | 21.4 | 19.2 | 7.7 | 4.8 | 2.5 |
| Stock-based compensation | 43.5 | 42.9 | 36.3 | 40.8 | 33.9 | 15.9 | 4.8 | 4.5 |
| Tax benefit from stock-based compensation | | | | | -26.8 | -0.6 | | |
| Deferred taxes | -3.5 | -1.4 | 12.6 | 7.8 | 33.6 | -3.4 | -13.6 | -9.7 |
| Change in working capital [+] | 27.5 | 16.7 | 37.0 | -20.5 | 8.9 | -17.4 | 13.2 | -4.7 |
| Accounts receivable | 12.1 | 9.1 | 7.0 | -18.0 | -6.5 | -32.5 | 5.8 | -3.1 |
| Other current assets | -63.6 | -12.0 | -0.9 | -0.2 | -1.4 | -1.7 | 0.6 | -0.8 |
| Deferred revenues | | | | | | 0.8 | 0.2 | -0.1 |
| Other | 79.1 | 19.7 | 30.9 | -2.3 | 16.8 | 16.1 | 6.6 | -0.7 |
| Other operating activities | -24.9 | -8.1 | -2.6 | -2.4 | 4.0 | 48.1 | 5.6 | -1.0 |
| Cash from operations | 247.3 | 137.2 | 276.1 | 197.8 | 148.0 | 46.1 | 51.7 | 35.8 |
| |
| Capital expenditures | -3.6 | -2.3 | -2.9 | -6.8 | -7.8 | -2.3 | -2.9 | -5.3 |
| Purchases of property and equipment | -3.6 | -2.3 | -2.9 | -6.8 | -7.8 | -2.3 | -2.9 | -5.3 |
| Acquisitions | | | -208.5 | | | -214.2 | -70.0 | |
| Sales of short-term investments, net [+] | | | | 1.5 | 8.5 | 4.0 | 0.0 | -0.3 |
| Purchases of short-term investments | | | | | | -2.4 | -6.5 | -6.5 |
| Sales of short-term investments | | | | 1.5 | 8.5 | 6.4 | 6.6 | 6.2 |
| Other cash from investing | | | | 0.0 | -55.9 | 2.6 | 3.7 | -3.3 |
| Cash from investing | -3.6 | -2.3 | -211.4 | -5.3 | -55.2 | -209.9 | -69.1 | -8.9 |
| |
| Repurchase of common stock, net | -54.6 | -64.9 | -136.8 | -133.8 | -80.6 | | -12.9 | -4.3 |
| Option exercises | 130.7 | 3.0 | 47.3 | 63.1 | 13.0 | 10.9 | 3.3 | 13.4 |
| Financing costs | -0.8 | | | | | | | |
| Other cash from financing | 227.2 | -24.8 | 79.4 | 51.3 | 42.5 | 198.8 | 7.9 | 28.0 |
| Cash from financing | 42.7 | -92.8 | -104.8 | -145.5 | -51.0 | 188.0 | -8.3 | 10.2 |
| |
| Free cash flow | 243.8 | 134.9 | 273.2 | 191.0 | 140.3 | 43.8 | 48.9 | 30.5 |
| Per share (diluted) | $12.79 | $7.58 | $14.56 | $10.39 | $7.69 | $2.67 | $2.98 | $1.87 |
| |
| Cash paid for interest | 0.6 | 2.1 | 2.7 | 3.6 | 2.9 | | | |
| Cash paid for income taxes | 27.7 | 13.8 | -10.1 | 23.5 | 4.8 | 1.0 | | |