| In millions, except per share items | Dec-31-22 | Dec-31-21 | Dec-31-20 | Dec-31-19 | Dec-31-18 | Dec-31-17 | Dec-31-16 | Dec-31-15 |
| | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K |
| Revenue from Contract with Customer, Product and Service [Extensible List] | | | | | | | | |
| Revenue from services | 2,806.6 | 1,676.7 | 836.4 | 822.2 | 816.5 | 865.0 | 833.5 | 779.2 |
| Revenue from services growth | 67.4% | 100.5% | 1.7% | 0.7% | -5.6% | 3.8% | 7.0% | 26.1% |
| Operating expenses: | | | | | | | | |
| Direct operating expenses | 2,178.9 | 1,301.7 | 633.7 | 618.2 | 606.9 | 636.5 | 611.8 | |
| Selling, general and administrative expenses | 324.2 | 215.3 | 173.8 | 182.0 | 180.2 | 187.4 | 179.8 | 161.3 |
| Bad debt expense | 9.6 | 4.8 | 3.0 | 2.0 | 2.2 | 1.8 | 0.6 | 1.0 |
| Depreciation and amortization | 12.6 | 9.9 | 12.7 | 14.1 | 11.8 | 10.2 | 9.2 | 8.1 |
| Restructuring costs (benefits) | 1.9 | 2.6 | 6.1 | 3.6 | 2.8 | 1.0 | 0.8 | 1.3 |
| Legal settlement charges | | | | 1.6 | | | | |
| Impairment charges | 5.6 | 2.1 | 16.2 | 16.3 | 22.4 | 14.4 | 24.3 | 2.1 |
| Total operating expenses | 2,533.5 | 1,537.3 | 845.6 | 837.9 | 829.4 | 853.3 | 827.4 | 746.9 |
| Income from operations | 273.1 | 139.3 | -9.2 | -15.7 | -12.9 | 11.7 | 6.2 | 20.6 |
| Operating margin | 9.7% | 8.3% | -1.1% | -1.9% | -1.6% | 1.4% | 0.7% | |
| |
| Other expenses (income): | | | | | | | | |
| Interest expense | -14.4 | -6.9 | -2.9 | -5.3 | -5.7 | -4.2 | -6.1 | -6.8 |
| Loss on early extinguishment of debt | 3.7 | | | 2.0 | 0.1 | 5.0 | 1.6 | |
| Other expense (income), net | -1.3 | -0.8 | 0.3 | -0.1 | -0.4 | -0.2 | -0.2 | -0.3 |
| Income tax expense | 67.9 | 1.2 | -0.2 | 31.7 | -2.5 | -34.5 | -4.2 | -0.8 |
| Net income attributable to common stockholders | 188.5 | 132.0 | -13.0 | -57.7 | -17.0 | 37.5 | 8.0 | 4.4 |
| |
| Other comprehensive income: | | | | | | | | |
| |
| Net income per share attributable to common stockholders - Basic | $5.09 | $3.60 | ($0.36) | ($1.61) | ($0.48) | $1.07 | $0.25 | $0.14 |
| Net income per share attributable to common stockholders - Diluted | $5.02 | $3.53 | ($0.36) | ($1.61) | ($0.48) | $1.01 | $0.15 | $0.14 |
| |
| Weighted average common shares outstanding: | | | | | | | | |
| Basic (shares) | 37.0 | 36.7 | 36.1 | 35.8 | 35.7 | 35.0 | 32.1 | 31.5 |
| Diluted (shares) | 37.5 | 37.4 | 36.1 | 35.8 | 35.7 | 36.2 | 36.2 | 32.2 |