| In millions, except per share items | 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 |
| Net income | 14.8 | 34.5 | 28.1 | 28.0 | 16.0 | 8.3 | 4.5 |
| Depreciation and amortization [+] | 1.8 | 1.7 | 1.5 | 1.3 | 1.3 | 0.9 | 0.7 |
| Depreciation | 1.3 | 1.1 | 1.0 | 0.8 | 0.7 | 0.6 | 0.7 |
| Amortization of intangible assets | 0.5 | 0.6 | 0.5 | 0.6 | 0.7 | 0.4 | |
| Stock-based compensation | 5.9 | 6.6 | 2.8 | 1.6 | 0.9 | 0.6 | 0.4 |
| Tax benefit from stock-based compensation | -0.1 | -0.6 | -0.5 | -1.0 | -0.5 | | -0.1 |
| Deferred taxes | -7.0 | 0.2 | 3.8 | -1.0 | -1.1 | -0.1 | -0.4 |
| Change in working capital [+] | 2.9 | -5.6 | -6.7 | -0.7 | -2.0 | -0.3 | 0.8 |
| Accounts receivable | 6.6 | -8.2 | -9.5 | -2.3 | -5.6 | -0.1 | 0.2 |
| Accrued expenses | -3.7 | 2.6 | 2.8 | 1.6 | 3.6 | -0.2 | 0.6 |
| Other operating activities | 5.5 | 13.5 | 26.7 | -0.2 | 12.7 | 2.5 | 9.7 |
| Cash from operations | 23.8 | 50.3 | 55.6 | 28.2 | 27.3 | 11.9 | 15.5 |
| |
| Capital expenditures | -1.6 | -2.6 | -3.2 | -3.2 | -0.9 | -3.9 | -1.8 |
| Purchases of property and equipment | -1.6 | -2.6 | -3.2 | -3.2 | -0.9 | -3.9 | -1.8 |
| Purchases of short-term investments, net | 527.6 | 73.7 | -232.9 | -160.3 | -174.9 | -49.4 | -89.2 |
| Purchases of short-term investments | -208.7 | -474.2 | -664.9 | -391.0 | -499.0 | -198.5 | -190.0 |
| Sales of short-term investments | 736.3 | 547.9 | 432.0 | 230.7 | 324.1 | 149.1 | 100.8 |
| Other cash from investing | -159.3 | -290.7 | -523.5 | -578.3 | -642.5 | -177.7 | |
| Cash from investing | 366.8 | -219.5 | -759.6 | -741.9 | -818.3 | -231.0 | -240.7 |
| |
| Issuance of common stock, net | -0.7 | -0.2 | | 67.6 | 50.4 | -0.5 | 14.2 |
| Option exercises | 5.3 | 3.0 | 1.6 | 1.6 | 1.8 | 0.3 | 0.1 |
| Other cash from financing | -429.8 | 201.2 | 866.2 | 686.2 | 745.5 | 251.0 | 204.3 |
| Cash from financing | -435.8 | 197.9 | 864.6 | 752.2 | 794.1 | 250.2 | 218.5 |
| |
| Free cash flow | 22.2 | 47.8 | 52.4 | 25.0 | 26.3 | 8.0 | 13.7 |
| Per share (diluted) | $1.49 | $3.28 | $3.83 | $2.17 | $2.56 | $1.24 | $3.40 |
| |
| Cash paid for interest | 74.0 | 63.8 | 34.6 | 17.0 | 9.1 | 5.5 | 4.0 |
| Cash paid for income taxes | 10.0 | 10.9 | 15.7 | 14.0 | 9.7 | 5.7 | 2.8 |