| In millions, except per share items | Dec-31-22 | Dec-31-21 | Dec-31-20 | Dec-31-19 | Dec-31-18 | Dec-31-17 | Dec-31-16 | Dec-31-15 |
| | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K |
| Net income | -22.3 | 20.4 | 19.1 | 46.5 | 117.1 | 106.9 | 99.4 | 106.5 |
| Depreciation and amortization [+] | 7.3 | 6.9 | 5.1 | 5.0 | 4.8 | 4.1 | 3.2 | 2.0 |
| Depreciation | 7.3 | 6.9 | 5.1 | 5.0 | 4.8 | 4.1 | 3.2 | 2.0 |
| Stock-based compensation | 4.7 | 5.8 | 8.7 | 13.0 | 12.8 | 10.5 | 10.3 | 17.4 |
| Tax benefit from stock-based compensation | | | | -0.6 | -5.4 | -5.8 | 1.2 | -5.3 |
| Deferred taxes | -12.1 | -4.3 | 2.8 | 2.0 | -3.7 | 1.3 | 4.7 | -0.7 |
| Change in working capital [+] | 44.4 | -4.3 | 26.9 | -29.6 | -5.2 | 7.8 | 1.8 | 0.3 |
| Accounts payable | | | | | | -0.3 | 2.8 | -3.7 |
| Income taxes | | | | | | | | 3.5 |
| Other | 44.4 | -4.3 | 26.9 | -29.6 | -5.2 | 8.2 | -1.0 | 0.6 |
| Other operating activities | 302.5 | 209.8 | -33.2 | 48.4 | 109.8 | 120.1 | 0.8 | 99.0 |
| Cash from operations | 324.5 | 234.4 | 29.3 | 84.6 | 230.1 | 245.0 | 121.4 | 219.3 |
| |
| Capital expenditures [+] | -4.9 | -7.2 | -17.2 | -11.3 | -6.7 | -4.6 | -8.2 | -11.9 |
| Purchases of property and equipment | -4.9 | -7.2 | -17.2 | -11.3 | -6.7 | -4.6 | -8.2 | -11.9 |
| Sales of property and equipment | 0.1 | 9.5 | 0.2 | 0.0 | 0.0 | 0.0 | 0.0 | 0.1 |
| Acquisitions | | | | | | | | -1.0 |
| Sales of short-term investments, net [+] | -3.2 | -77.4 | 1,222.2 | 224.9 | 74.2 | 66.1 | 11.1 | -40.5 |
| Purchases of short-term investments | -200.0 | -450.4 | -1,074.6 | -221.6 | -437.6 | -190.6 | -320.1 | -265.7 |
| Sales of short-term investments | 196.8 | 373.0 | 2,296.8 | 446.5 | 511.9 | 256.7 | 331.3 | 225.3 |
| Other cash from investing | -140.9 | -154.3 | -1,183.1 | -185.3 | -279.8 | -147.3 | -177.3 | -29.8 |
| Cash from investing | -148.9 | -229.4 | 22.0 | 28.3 | -212.3 | -85.7 | -174.3 | -83.1 |
| |
| Cash dividends paid | -23.8 | -24.2 | -24.5 | -26.1 | -25.5 | -24.0 | -24.2 | -22.3 |
| Repurchase of common stock, net | -11.6 | -1.6 | -28.9 | -66.2 | -25.3 | -18.1 | -8.5 | -18.6 |
| Option exercises | 0.1 | 0.1 | | 0.2 | 0.1 | | 0.1 | 0.5 |
| Financing costs | -0.1 | -3.4 | | | | | | |
| Other cash from financing | -2.1 | 90.8 | -2.8 | -4.7 | -14.0 | -9.4 | -5.5 | -13.2 |
| Cash from financing | -37.5 | 68.3 | -56.3 | -97.2 | -64.9 | -51.5 | -38.4 | -54.6 |
| |
| Free cash flow | 319.6 | 227.2 | 12.1 | 73.3 | 223.4 | 240.4 | 113.2 | 207.4 |
| Per share (diluted) | $10.39 | $7.26 | $0.38 | $2.14 | $6.24 | $6.71 | $3.17 | $5.78 |
| |
| Cash paid for interest | 5.8 | 0.1 | 0.1 | 0.2 | 0.3 | 0.3 | 0.4 | 1.0 |
| Cash paid for income taxes | 16.7 | 1.4 | 1.4 | 39.7 | 42.7 | 69.3 | 69.0 | 65.4 |