| In millions, except per share items | Dec-31-17 | Dec-31-16 | Dec-31-15 | Dec-31-14 | Dec-31-13 | Dec-31-12 | Dec-31-11 | Dec-31-10 |
| | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K |
| Net income | 53.1 | 21.0 | 14.0 | -3.1 | 2.6 | 18.7 | 19.0 | 12.7 |
| Depreciation and amortization | 147.3 | 142.7 | 118.0 | 93.8 | 61.9 | 29.1 | 19.0 | 13.0 |
| Stock-based compensation | 54.3 | 66.5 | 64.1 | 55.6 | 42.6 | 27.2 | 18.9 | 14.5 |
| Tax benefit from stock-based compensation | | -9.0 | -12.9 | -10.1 | -6.9 | -14.2 | -14.2 | -9.2 |
| Deferred taxes | 7.3 | -9.9 | -8.5 | -11.7 | -7.0 | -0.9 | -3.0 | 1.0 |
| Change in working capital [+] | -15.8 | -24.1 | 20.4 | 24.1 | 0.2 | 14.1 | 17.7 | 10.2 |
| Accounts receivable | -7.9 | -13.5 | -25.3 | -34.4 | -3.4 | -12.6 | -12.1 | -5.3 |
| Other current assets | -12.5 | 5.1 | 4.2 | 4.3 | 3.3 | 12.1 | 11.8 | 5.5 |
| Accounts payable | 4.5 | -4.8 | 2.8 | 2.5 | -0.2 | 0.0 | 0.7 | -1.0 |
| Accrued expenses | -3.7 | -0.9 | 8.2 | 10.1 | 0.0 | 11.9 | 10.9 | 4.4 |
| Deferred revenues | 0.1 | -11.4 | 3.2 | 3.2 | -3.1 | 3.0 | 10.0 | 7.9 |
| Other | 3.7 | 1.4 | 27.3 | 38.4 | 3.7 | -0.2 | -3.6 | -1.3 |
| Other operating activities | -5.1 | -4.6 | -31.3 | 0.5 | -0.1 | -3.9 | 3.3 | 2.6 |
| Cash from operations | 241.1 | 182.6 | 163.8 | 149.1 | 93.3 | 70.2 | 60.8 | 44.7 |
| |
| Capital expenditures [+] | -162.9 | -158.5 | -185.0 | -129.6 | -67.4 | -39.6 | -24.5 | -19.8 |
| Purchases of property and equipment | -80.1 | -69.0 | -87.2 | -76.1 | -38.3 | -23.9 | -16.7 | -15.9 |
| Capitalized product costs | -82.8 | -89.5 | -97.8 | -53.5 | -29.1 | -15.7 | -7.8 | -3.9 |
| Sales of property and equipment | | | | | | | | 0.4 |
| Acquisitions | -41.1 | -16.9 | -39.9 | | -410.2 | -5.8 | -34.9 | |
| Sales of short-term investments, net [+] | | | 29.8 | | 56.2 | 41.4 | 2.4 | -34.7 |
| Purchases of short-term investments | | | | | | -118.9 | -165.7 | -145.4 |
| Sales of short-term investments | | | 29.8 | | 56.2 | 160.3 | 168.1 | 110.7 |
| Other cash from investing | | 0.5 | -4.0 | 2.3 | -3.6 | 3.8 | 3.7 | 0.5 |
| Cash from investing | -204.0 | -174.9 | -199.1 | -127.3 | -424.9 | -0.1 | -53.2 | -53.6 |
| |
| Financing costs | | | | | -1.7 | | -0.7 | |
| Other cash from financing | -20.1 | -2.0 | 103.8 | -12.8 | 240.0 | 27.1 | 13.7 | 14.1 |
| Cash from financing | -20.1 | -2.0 | 103.8 | -12.8 | 241.7 | 27.1 | 14.4 | 14.1 |
| |
| Free cash flow | 161.0 | 113.6 | 76.6 | 73.0 | 55.0 | 46.3 | 44.1 | 28.8 |
| Per share (diluted) | $1.92 | $0.60 | ($0.54) | $0.51 | $0.68 | $0.83 | $1.01 | $0.71 |
| |
| Cash paid for interest | 5.1 | 4.6 | 5.7 | 4.5 | 2.9 | | 0.2 | |
| Cash paid for income taxes | 2.6 | 0.3 | 0.6 | 1.9 | 1.3 | 3.9 | 2.7 | 1.6 |