| 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 | 124.4 | 77.8 | 98.7 | 67.3 | 42.9 | 29.2 | 22.1 | 5.7 |
| Depreciation and amortization [+] | 5.5 | 6.0 | 6.4 | 6.4 | 5.6 | 5.1 | 2.2 | 3.0 |
| Depreciation | 5.5 | 6.0 | 6.4 | 6.4 | 5.6 | 5.1 | 3.8 | 3.3 |
| Stock-based compensation | 8.7 | 7.3 | 7.2 | 7.8 | 5.3 | 4.2 | 2.9 | 1.4 |
| Deferred taxes | 3.8 | -4.9 | 6.8 | 0.5 | 35.8 | 14.2 | 12.9 | 4.2 |
| Change in working capital | 28.9 | 18.8 | -4.2 | 8.8 | -21.4 | 3.0 | -0.6 | -185.5 |
| Other | 28.9 | 18.8 | -4.2 | 8.8 | -21.4 | 3.0 | -0.6 | -185.5 |
| Other operating activities | -16.7 | -44.3 | 2.8 | 38.9 | -19.2 | 6.4 | -9.9 | 193.0 |
| Cash from operations | 154.6 | 60.7 | 117.7 | 129.6 | 48.9 | 62.0 | 29.5 | 21.9 |
| |
| Capital expenditures | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Purchases of short-term investments, net | -513.9 | -429.5 | -5.1 | 100.9 | 159.9 | -129.4 | 19.2 | -166.1 |
| Purchases of short-term investments | -1,145.2 | -830.3 | -309.5 | -104.7 | -378.1 | -297.7 | -159.6 | -280.1 |
| Sales of short-term investments | 631.3 | 400.8 | 304.4 | 205.6 | 538.0 | 168.3 | 178.8 | 114.0 |
| Other cash from investing | 101.4 | 87.0 | -316.3 | -275.5 | -405.4 | -382.4 | -190.1 | -129.0 |
| Cash from investing | -412.5 | -342.5 | -321.3 | -174.6 | -245.6 | -511.8 | -170.9 | -295.1 |
| |
| Issuance of common stock, net | | | | | 55.6 | | | 24.6 |
| Option exercises | 5.0 | | | 1.0 | | | | |
| Other cash from financing | 596.6 | 561.4 | 212.2 | 52.4 | 140.9 | 423.4 | 176.9 | 157.4 |
| Cash from financing | 591.6 | 561.4 | 212.2 | 51.4 | 196.5 | 423.4 | 176.9 | 182.1 |
| |
| Free cash flow | 154.6 | 60.7 | 117.7 | 129.6 | 48.9 | 62.0 | 29.5 | 21.9 |
| Per share (diluted) | $2.71 | $1.12 | $2.26 | $2.66 | $1.13 | $1.65 | $0.87 | $0.79 |
| |
| Cash paid for interest | 10.0 | 23.5 | 46.1 | 28.3 | 15.1 | 7.9 | 6.6 | 3.5 |
| Cash paid for income taxes | 30.9 | 27.7 | 16.0 | 13.2 | 0.4 | 0.7 | 0.6 | 0.2 |