| In millions, except per share items | Sep-30-18 | Jun-30-18 | Mar-31-18 | Dec-31-17 | Sep-30-17 | Jun-30-17 | Mar-31-17 | Dec-31-16 |
| | 10-Q | 10-Q | 10-Q | 10-K | 10-Q | 10-Q | 10-Q | 10-K |
| Cash flows from operating activities: | | | | | | | | |
| Net loss | -219.1 | -190.1 | -45.1 | -54.9 | -96.7 | -102.8 | -85.9 | -28.9 |
| Adjustments to reconcile net loss to net cash from (used in) operating activities: | | | | | | | | |
| Depreciation, depletion and amortization | 86.0 | 97.4 | 110.5 | 121.1 | 186.3 | 189.1 | 184.8 | 185.3 |
| Share-based compensation | 1.2 | 2.6 | 3.7 | 3.2 | 5.5 | 5.5 | 6.4 | 7.6 |
| Amortization of deferred financing costs | 9.1 | 10.7 | 11.2 | 10.8 | 11.4 | 10.1 | 10.9 | 11.5 |
| Gain on derivative instruments | | | | -1.9 | -32.8 | -22.7 | -29.0 | -24.1 |
| (Gain) loss on foreign exchange | -0.8 | -0.1 | 1.3 | 3.1 | 2.5 | 2.3 | | |
| Income from equity affiliates | -3.7 | -4.1 | -5.5 | -5.9 | -5.7 | -8.5 | | |
| Changes in operating assets and liabilities: | | | | | | | | |
| Receivables | 39.1 | 38.1 | 20.6 | 35.6 | -15.4 | -0.4 | 17.9 | -4.4 |
| Inventories | -5.3 | -20.7 | -1.9 | 20.3 | 24.5 | 14.4 | 25.5 | 13.0 |
| Accounts payable and accrued expenses | 10.9 | -13.7 | 10.2 | -20.2 | -18.1 | -6.4 | -19.1 | 10.5 |
| Deferred revenue | -17.6 | -15.2 | -19.4 | -23.1 | -17.8 | -19.2 | -8.5 | -7.4 |
| Other assets and liabilities | -17.3 | -17.7 | -0.4 | 20.5 | 7.8 | 4.7 | 38.6 | 13.2 |
| Net cash provided by operating activities | 101.6 | 63.9 | 106.0 | 114.2 | 88.0 | 120.2 | 130.7 | 151.9 |
| |
| Cash flows from investing activities: | | | | | | | | |
| Additions to property, plant and equipment | -35.0 | -33.7 | -34.0 | -35.0 | -40.9 | -47.0 | -47.8 | -46.1 |
| Proceeds from sales of restricted investments | 29.8 | 35.7 | 34.4 | | 33.7 | 46.8 | 39.9 | |
| Proceeds from sales of assets | 3.2 | 2.1 | 0.4 | | 0.8 | 7.0 | 6.6 | |
| Net cash (used in) provided by investing activities | -28.2 | -30.2 | -33.5 | 10.0 | 7.7 | 2.6 | 12.9 | -155.7 |
| |
| Cash flows from financing activities: | | | | | | | | |
| Borrowings from long-term debt, net of debt discount | | | | | | | | |
| Repayments of long-term debt | -90.8 | -104.8 | -70.5 | -82.1 | -90.6 | -96.7 | -83.7 | -70.4 |
| Borrowings on revolving lines of credit | | 284.5 | 224.0 | 275.3 | 345.7 | 341.3 | 469.2 | 423.5 |
| Repayments of revolving lines of credit | -90.8 | -104.8 | -70.5 | -82.1 | -90.6 | -96.7 | -83.7 | -70.4 |
| Debt issuance costs and other refinancing costs | | -2.7 | | | | | | -8.8 |
| Net cash provided by (used in) financing activities | -17.4 | -21.1 | -70.0 | -82.8 | -82.3 | -103.6 | -89.4 | 40.1 |
| |
| Supplemental disclosures of cash flow information: | | | | | | | | |
| Non-cash transactions: | | | | | | | | |
| Capital leases and other financing sources | 1.4 | | | 1.3 | 8.0 | | 27.8 | 27.4 |
| Cash and cash equivalents, including restricted cash, end of period | | | | | | | | |
| Cash and cash equivalents | | | | | | | | |
| Restricted cash in Restricted investments, reclamation deposits and bond collateral | | | | | | | | |