| 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 | 72.7 | 117.0 | 182.8 | 144.2 | 158.1 | 237.6 | 313.3 | 253.0 |
| Depreciation and amortization [+] | 12.6 | 20.0 | 28.3 | 21.0 | 18.4 | 16.1 | 14.8 | 13.7 |
| Depreciation | 12.6 | 20.0 | 28.3 | 21.0 | 18.4 | 16.1 | 14.8 | 13.7 |
| Asset impairment charges | 3.4 | 12.8 | 1.5 | 1.5 | 9.7 | | | |
| Stock-based compensation | 56.8 | 46.6 | 51.6 | 57.7 | 51.5 | 47.5 | 54.1 | 53.2 |
| Tax benefit from stock-based compensation | | | | | | | -19.1 | -13.0 |
| Deferred taxes | -4.7 | -3.0 | 0.8 | 20.5 | 2.0 | -6.2 | 0.7 | -3.0 |
| Change in working capital [+] | -15.3 | 46.6 | -46.2 | -11.9 | 50.4 | -11.7 | -36.4 | 13.3 |
| Restricted cash | | | | | | 9.7 | 44.8 | -28.4 |
| Accounts receivable | -2.8 | 54.0 | -25.6 | -3.0 | 92.6 | -3.8 | -75.4 | |
| Other | -12.6 | -7.4 | -20.7 | -8.9 | -42.2 | -17.6 | -5.8 | 41.7 |
| Other operating activities | 62.6 | -74.0 | 138.3 | -182.2 | -202.2 | -49.3 | 17.6 | |
| Cash from operations | 188.0 | 166.0 | 357.0 | 50.9 | 87.9 | 234.0 | 345.0 | 286.9 |
| |
| Capital expenditures [+] | -8.6 | -5.8 | -2.6 | -6.8 | -15.7 | -29.6 | -35.6 | -16.9 |
| Purchases of property and equipment | -8.6 | -5.8 | -2.6 | -6.8 | -15.7 | -29.6 | -35.6 | -16.9 |
| Sales of property and equipment | 2.3 | | | | | | | |
| Sales of short-term investments | 173.4 | 161.3 | 125.7 | 86.9 | 98.2 | 36.7 | 164.2 | 262.2 |
| Sales of short-term investments | 173.4 | 161.3 | 125.7 | 86.9 | 98.2 | 36.7 | 164.2 | 262.2 |
| Other cash from investing | -68.4 | -162.4 | -112.8 | -292.5 | -6.6 | -29.6 | -167.7 | -219.6 |
| Cash from investing | 98.7 | -6.9 | 10.3 | -212.4 | 75.9 | -22.6 | -39.1 | 25.6 |
| |
| Cash dividends paid | -65.6 | -74.3 | -81.2 | -154.0 | -152.8 | -144.0 | -115.3 | -96.0 |
| Repurchase of common stock, net | -115.6 | -155.8 | -133.4 | -35.8 | -49.8 | -80.3 | -131.0 | -72.1 |
| Option exercises | | | | | | | | 0.1 |
| Other cash from financing | 5.7 | 5.6 | -97.2 | 1.1 | -0.3 | 4.8 | 19.1 | 13.3 |
| Cash from financing | -175.5 | -224.5 | -311.8 | -188.7 | -202.9 | -219.5 | -227.2 | -155.0 |
| |
| Free cash flow | 179.5 | 160.2 | 354.4 | 44.1 | 72.2 | 204.3 | 309.4 | 270.0 |
| Per share (diluted) | $2.76 | $2.19 | $4.40 | $0.53 | $0.87 | $2.45 | $3.66 | $3.15 |
| |
| Cash paid for interest | 5.5 | 5.5 | 7.9 | 10.3 | 10.3 | 10.3 | 10.3 | 10.3 |
| Cash paid for income taxes | 39.2 | 53.0 | 59.1 | 85.3 | 77.0 | 152.3 | 165.2 | 124.2 |