| 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 |
| Revenue | 330.5 | 333.1 | 291.9 | 259.3 | 237.5 | 197.7 | 154.0 | 94.9 |
| Revenue growth | -0.8% | 14.1% | 12.5% | 9.2% | 20.1% | 28.3% | 62.4% | 189.1% |
| Cost of revenue | 203.7 | 197.3 | 148.9 | 124.4 | 110.8 | 82.3 | 67.4 | 43.6 |
| Selling, general and administrative expenses | 90.5 | 100.5 | 77.4 | 71.7 | 62.5 | 53.6 | 40.6 | 23.9 |
| Operating income | -57.8 | 35.4 | 66.2 | 63.9 | 64.1 | 62.0 | 46.1 | 26.8 |
| Operating margin | -17.5% | 10.6% | 22.7% | 24.7% | 27.0% | 31.3% | 29.9% | 28.3% |
| Interest income | 1.1 | 0.5 | 0.7 | 0.4 | | 0.1 | 0.7 | 2.8 |
| Interest expense | -4.5 | -3.0 | | | | | | |
| Other income (expense), net | 2.2 | -0.6 | -1.4 | 0.0 | 0.2 | 0.1 | | |
| Total interest and other income (expense), net | 1.0 | -3.1 | -2.1 | 0.4 | 0.2 | | | |
| Income before provision for income taxes | -59.1 | 32.3 | 65.5 | 64.3 | 64.3 | 62.1 | 45.4 | 24.1 |
| Provision for income taxes | 20.1 | 14.1 | 26.1 | 24.9 | 23.5 | 23.1 | 16.2 | 10.2 |
| Tax rate | | 43.6% | 39.8% | 38.8% | 36.6% | 37.2% | 35.8% | 42.3% |
| Net income | -79.1 | 18.2 | 39.4 | 39.3 | 40.8 | 39.0 | 29.1 | 13.9 |
| |
| Net income per share: | | | | | | | | |
| Basic (dollars per common share) | ($1.61) | $0.36 | $0.72 | $0.74 | $0.78 | $0.77 | $0.61 | $0.24 |
| Diluted (dollars per common share) | ($1.61) | $0.36 | $0.71 | $0.72 | $0.76 | $0.74 | $0.57 | $0.23 |
| |
| Weighted-average shares used in computing net income per share: | | | | | | | | |
| Basic (in shares) | 49.2 | 50.5 | 54.4 | 53.4 | 52.0 | 49.8 | 32.0 | 5.7 |
| Diluted (in shares) | 49.2 | 51.0 | 55.4 | 54.8 | 53.7 | 51.8 | 35.9 | 7.2 |
| |
| Cash dividend (in usd per share) | $0.05 | | | | | | | |