| In millions, except per share items | Dec-31-14 | Dec-31-13 | Dec-31-12 | Dec-31-11 | Dec-31-10 | Dec-31-09 | Dec-31-08 | Dec-31-07 |
| | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K |
| Revenues | 529.2 | 427.3 | 326.5 | 316.2 | 286.0 | 275.9 | 320.9 | 290.3 |
| Revenues growth | 23.8% | 30.9% | 3.3% | 10.6% | 3.6% | -14.0% | 10.6% | 17.8% |
| Costs and expenses: | | | | | | | | |
| Operating costs (exclusive of depreciation and amortization) | 397.6 | 306.0 | 233.3 | 219.1 | 194.6 | 187.3 | | |
| Depreciation and amortization expense | 12.6 | 11.4 | 8.9 | 8.2 | 6.5 | 6.0 | | |
| Selling, general and administrative expense | 98.3 | 85.0 | 76.8 | 68.4 | 71.2 | 81.1 | | |
| Total costs and expenses | 508.5 | 402.5 | 638.4 | 591.6 | 545.2 | 274.4 | | |
| Operating income | 20.7 | 24.8 | 7.5 | 20.5 | 13.7 | 1.5 | | |
| Operating margin | 3.9% | 5.8% | 2.3% | 6.5% | 4.8% | 0.6% | | |
| Interest income and other income (expense), net | -0.1 | -0.6 | -0.2 | -0.1 | | | | |
| Interest expense | -1.8 | -1.3 | -1.1 | -1.0 | -0.9 | -1.4 | | |
| Income from continuing operations before income taxes | 18.8 | 22.8 | 6.2 | 19.3 | 13.3 | 0.6 | 25.6 | 18.4 |
| Income tax expense | 7.4 | 8.8 | 5.4 | -4.7 | | 3.4 | | |
| Tax rate | 39.5% | 38.6% | 87.0% | | | 580.5% | | |
| Income from continuing operations | 11.4 | 14.0 | 0.8 | 24.0 | 9.5 | -2.8 | | |
| Net income | 11.4 | 14.0 | 0.8 | 24.0 | 9.5 | -2.8 | | |
| |
| Basic earnings (loss) per common share: | | | | | | | | |
| |
| Net income | $0.30 | $0.37 | $0.02 | $0.65 | $0.26 | ($0.08) | | |
| |
| Diluted earnings (loss) per common share: | | | | | | | | |
| Net income | $0.30 | $0.37 | $0.02 | $0.64 | $0.26 | ($0.08) | | |
| |
| Weighted-average number of common and common equivalent shares used in computing earnings (loss) per common share: | | | | | | | | |
| Basic (in shares) | 37.6 | 37.4 | 37.3 | 37.0 | 36.8 | 36.6 | | |
| Diluted (in shares) | 37.9 | 37.6 | 37.5 | 37.3 | 36.9 | 36.6 | | |