| 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-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K |
| Revenues and other income | | | | | | | | |
| Revenues | | | | | | | | |
| Total revenues and other income | 194.2 | 129.0 | 210.3 | 202.8 | 246.3 | 279.2 | 439.6 | 350.9 |
| Total revenues and other income growth | 50.6% | -38.7% | 3.7% | -17.7% | -11.8% | -36.5% | 25.3% | -2.0% |
| Operating expenses | | | | | | | | |
| Depreciation, depletion and amortization | 19.1 | 9.2 | 14.9 | 21.7 | 23.4 | 28.6 | 57.3 | 58.6 |
| General and administrative expenses | 17.4 | 14.3 | 16.7 | 16.5 | 18.5 | 17.0 | 7.0 | 7.3 |
| Asset impairments | 5.1 | 135.9 | 148.2 | 18.3 | 3.0 | 15.9 | 384.5 | 26.2 |
| Total operating expenses | 95.6 | 209.0 | 245.4 | 115.5 | 94.6 | 218.5 | 747.0 | 240.7 |
| Income from operations | 147.8 | -43.9 | 51.3 | 192.5 | 176.6 | 181.2 | -170.4 | 176.1 |
| Operating margin | 76.1% | -34.0% | 24.4% | 95.0% | 71.7% | 64.9% | -38.8% | 50.2% |
| |
| Other expenses, net | | | | | | | | |
| Interest expense, net | -38.9 | -41.0 | -47.5 | -70.2 | -82.0 | -90.0 | -87.9 | -79.1 |
| Loss on extinguishment of debt | | | -29.3 | | -7.9 | | | |
| Net income | 108.9 | -84.8 | -49.9 | 140.0 | 88.7 | 96.9 | -260.2 | 96.7 |
| Less: income attributable to preferred unitholders | -31.6 | -30.2 | -30.0 | -30.0 | -25.5 | | | |
| Net income attributable to common unitholders and the general partner | 75.7 | -112.7 | -53.4 | 107.3 | 63.2 | 96.9 | -571.7 | 106.7 |
| Net income attributable to common unitholders | 75.7 | -112.7 | -53.4 | 107.3 | 63.2 | 96.9 | -571.7 | 106.7 |
| Net income attributable to the general partner | 1.5 | -2.3 | -1.1 | 2.2 | 1.3 | 1.7 | -12.2 | 2.2 |
| |
| Net income per common unit (see Note 5) | | | | | | | | |
| Basic (in dollars per share) | $6.14 | ($9.20) | ($4.35) | $8.77 | $5.06 | $7.78 | ($45.75) | |
| Diluted (in dollars per share) | $4.81 | ($9.20) | ($4.35) | $6.76 | $3.96 | $7.78 | ($45.75) | |
| Net income | 108.9 | -84.8 | -49.9 | 140.0 | 88.7 | 96.9 | -260.2 | 96.7 |
| |
| Comprehensive income (loss) from unconsolidated investment and other | | | | | | | | |
| Comprehensive income | | | | | | | | |