| In millions, except per share items | Jun-30-23 | Mar-31-23 | Dec-31-22 | Sep-30-22 | Jun-30-22 | Mar-31-22 | Dec-31-21 | Sep-30-21 |
| | 10-Q | 10-Q | 10-K | 10-Q | 10-Q | 10-Q | 10-K | 10-Q |
| OPERATING ACTIVITIES: | | | | | | | | |
| Net income (loss) | 57.1 | 36.8 | 4.6 | -33.2 | -17.3 | -13.9 | -3.8 | 4.0 |
| Deferred income taxes | 5.9 | 4.9 | 1.8 | 3.6 | 1.6 | 1.6 | 0.0 | -2.1 |
| Equity income (loss) – Sunrise Energy | 0.0 | -0.4 | -0.4 | -0.7 | -0.6 | -0.5 | -0.4 | 0.0 |
| Cash distribution - Sunrise Energy | | 0.6 | | | | | | |
| Depreciation, depletion and amortization | 61.3 | 55.3 | 46.9 | 42.0 | 40.6 | 39.2 | 40.0 | 39.3 |
| Loss on sale of assets | 0.2 | -0.3 | -0.3 | | -0.4 | 0.1 | | |
| Change in fair value of interest rate swaps | | | | | | | | |
| Amortization of debt issuance costs | 4.3 | 4.1 | 3.6 | 3.2 | 2.8 | 2.6 | 2.6 | 2.5 |
| Asset retirement obligations accretion | 1.4 | 1.2 | 1.0 | 1.1 | 1.3 | 1.4 | 1.5 | 1.5 |
| Cash paid on asset retirement obligation reclamation | -2.9 | -2.8 | -3.2 | -2.5 | -1.2 | -0.7 | | |
| Stock-based compensation | 3.2 | 2.4 | 1.3 | 0.4 | 0.5 | 0.8 | 1.0 | 1.1 |
| Provision for loss on customer contracts | | | | | | 0.2 | | |
| Other | 0.9 | 1.0 | 0.7 | 0.4 | -0.1 | -0.3 | -0.4 | -2.9 |
| Change in operating assets and liabilities: | | | | | | | | |
| Accounts receivable | -4.3 | -17.8 | -16.3 | -0.3 | -2.8 | -1.8 | 0.8 | -0.6 |
| Inventory | -29.1 | -28.8 | -25.9 | -2.4 | 18.5 | 25.3 | 17.0 | 25.5 |
| Parts and supplies | -9.6 | -7.7 | -6.3 | -5.2 | -3.0 | -2.2 | -1.1 | -0.6 |
| Prepaid expenses | -6.4 | -7.2 | -5.9 | -3.0 | -4.4 | -3.3 | -5.2 | -4.6 |
| Accounts payable and accrued liabilities | 8.1 | 19.5 | 24.0 | 11.2 | 9.3 | 13.1 | 10.8 | 13.0 |
| Deferred revenue | 0.1 | 3.0 | | | | | | |
| Cash provided by operating activities | 98.1 | 77.3 | 54.2 | 24.9 | 35.4 | 48.0 | 48.0 | 55.5 |
| |
| INVESTING ACTIVITIES: | | | | | | | | |
| Capital expenditures | -61.7 | -58.4 | -54.0 | -48.3 | -40.1 | -31.4 | -28.1 | -24.8 |
| Proceeds from sale of equipment | 0.0 | 0.5 | 0.7 | | 0.8 | 0.1 | | |
| Cash used in investing activities | -61.8 | -57.9 | -53.4 | -47.0 | -38.8 | -30.8 | -27.5 | -24.8 |
| |
| FINANCING ACTIVITIES: | | | | | | | | |
| Payments on bank debt | -100.5 | -96.1 | -78.2 | -44.9 | -42.1 | -46.2 | -46.2 | -46.2 |
| Borrowings of bank debt | 44.0 | 51.2 | 51.7 | 43.7 | 42.7 | 30.3 | 20.3 | 14.3 |
| Issuance of convertible note | | | | | 1.0 | | | |
| Issuance of related party convertible notes payable | | | | | 9.0 | | | |
| Debt issuance costs | -3.1 | -3.1 | | -2.1 | | -1.0 | | |
| Taxes paid on vesting of RSUs | | -1.1 | | | | | -0.3 | |
| Cash (used in) provided by financing activities | -42.4 | -20.7 | -0.2 | 24.8 | 9.8 | -17.3 | -26.7 | -32.5 |
| (Decrease) increase in cash, cash equivalents, and restricted cash | -0.1 | 4.7 | | | 6.5 | 1.7 | | |
| |
| CASH, CASH EQUIVALENTS, AND RESTRICTED CASH CONSIST OF THE FOLLOWING: | | | | | | | | |
| Cash and cash equivalents | | | | | | | | |
| Restricted cash | | | | | | | | |
| SUPPLEMENTAL CASH FLOW INFORMATION: | | | | | | | | |
| Cash paid for interest | 9.1 | 9.2 | 8.1 | 6.8 | 8.3 | 8.6 | 8.7 | 9.5 |
| SUPPLEMENTAL NON-CASH FLOW INFORMATION: | | | | | | | | |
| Change in capital expenditures included in accounts payable and prepaid expense | 1.9 | 2.9 | 3.4 | 5.1 | 6.9 | 11.0 | 8.5 | 6.0 |
| Convertible notes payable and related party convertible notes payable converted to common stock | | | | | 10.0 | | | |