| In millions, except per share items | Dec-31-21 | Dec-31-20 | Dec-31-19 | Dec-31-18 | Dec-31-17 | Dec-31-16 | Dec-31-15 | Dec-31-14 |
| | 10-Q | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K |
| ASSETS | | | | | | | | |
| CURRENT ASSETS: | | | | | | | | |
| Cash and cash equivalents | 33.8 | 154.3 | 3.5 | 4.0 | 2.0 | 2.5 | 2.3 | 2.2 |
| Accounts receivable, net of allowance for credit losses of $3,879 and $3,276, respectively | 87.0 | 74.2 | 80.2 | 74.9 | 66.0 | 61.2 | 60.2 | 55.8 |
| Prepaid expenses | 12.8 | 9.3 | 9.0 | 7.3 | 8.3 | 8.0 | 7.7 | 8.8 |
| Inventory | 9.7 | 7.9 | 7.7 | 6.5 | 6.5 | 4.9 | 4.3 | 4.4 |
| Other current assets | 3.2 | 1.3 | 1.2 | 2.0 | 1.1 | 1.3 | 1.6 | 4.9 |
| Total current assets | 146.5 | 247.3 | 102.8 | 97.1 | 84.4 | 78.6 | 76.7 | 78.7 |
| Property, plant and equipment, net of accumulated depreciation and amortization of $1,016,382 and $973,094, respectively | 644.6 | 510.5 | 443.8 | 404.6 | 361.5 | 398.5 | 402.3 | 414.5 |
| Operating lease right-of-use assets | 93.8 | 95.3 | 108.0 | | | | | |
| Goodwill | 232.9 | 194.9 | 185.8 | 162.7 | 122.6 | 119.9 | 119.0 | 119.2 |
| Intangible assets, net | 93.7 | 58.3 | 58.7 | 34.8 | 8.1 | 7.7 | 9.3 | 11.8 |
| Restricted cash and assets | 2.1 | 1.8 | 1.6 | 1.2 | 1.2 | 1.0 | 2.3 | 6.6 |
| Cost method investments | 26.0 | 24.6 | 11.6 | 11.1 | 13.1 | 13.5 | 11.9 | 24.5 |
| Deferred income taxes | 44.0 | 61.2 | 8.6 | 9.6 | 11.6 | | | |
| Other non-current assets | 26.0 | 24.6 | 11.6 | 11.1 | 13.1 | 13.5 | 11.9 | 24.5 |
| Total assets | 1,283.6 | 1,193.9 | 932.2 | 732.4 | 614.9 | 631.5 | 633.7 | 669.8 |
| |
| LIABILITIES AND STOCKHOLDERS' EQUITY | | | | | | | | |
| CURRENT LIABILITIES: | | | | | | | | |
| Current maturities of debt | 9.9 | 9.2 | 4.3 | 2.3 | 4.9 | 4.7 | 1.4 | 1.7 |
| Current operating lease liabilities | 7.3 | 8.5 | 9.4 | | | | | |
| Accounts payable | 63.1 | 49.2 | 64.4 | 57.3 | 47.1 | 45.0 | 44.9 | 48.5 |
| Accrued payroll and related expenses | 22.2 | 17.3 | 14.4 | 11.0 | 12.2 | 12.5 | 8.2 | 6.3 |
| Accrued interest | 2.0 | 2.1 | 2.0 | 2.4 | 2.1 | 4.7 | 12.3 | 11.1 |
| Contract liabilities | 3.4 | 2.7 | 2.3 | 3.1 | 1.8 | | | |
| Current accrued capping, closure and post-closure costs | 7.9 | 10.3 | 10.2 | 11.6 | 3.0 | 0.7 | 0.7 | 2.2 |
| Other accrued liabilities | 36.3 | 31.9 | 23.6 | 23.8 | 17.4 | 14.9 | 17.8 | 16.7 |
| Total current liabilities | 152.2 | 131.2 | 130.6 | 111.5 | 88.6 | 82.4 | 85.3 | 86.4 |
| Debt, less current portion | 542.5 | 530.4 | 509.0 | 542.0 | 477.6 | 504.0 | 506.0 | 534.1 |
| Operating lease liabilities, less current portion | 56.4 | 61.0 | 70.7 | | | | | |
| Accrued capping, closure and post-closure costs, less current portion | 79.0 | 72.3 | 61.7 | 61.4 | 59.3 | 43.5 | 40.3 | 37.6 |
| Deferred income taxes | 0.9 | 0.9 | 2.6 | 2.5 | 2.3 | 6.2 | 5.6 | 7.1 |
| Other long-term liabilities | 30.2 | 36.0 | 34.8 | 30.8 | 25.1 | 20.0 | 18.0 | 16.6 |
| |
| COMMITMENTS AND CONTINGENCIES | | | | | | | | |
| STOCKHOLDERS' EQUITY: | | | | | | | | |
| Common stock | | | | | | | | |
| Additional paid-in capital | 652.0 | 639.2 | 485.3 | 373.7 | 356.6 | 348.4 | 344.5 | 340.8 |
| Accumulated deficit | -225.0 | -266.1 | -357.0 | -388.7 | -395.1 | -373.3 | -366.5 | -353.5 |
| Accumulated other comprehensive income (loss), net of tax | -5.1 | -11.5 | -6.0 | -1.3 | 0.2 | -0.1 | 0.0 | 0.1 |
| Total stockholders' equity | 422.5 | 362.1 | 122.8 | -15.8 | -37.9 | -24.5 | -21.5 | -12.3 |
| Total liabilities and stockholders' equity | 1,283.6 | 1,193.9 | 932.2 | 732.4 | 614.9 | 631.5 | 633.7 | 669.8 |