| In millions, except per share items | Dec-31-19 | Dec-31-18 | Dec-31-17 | Dec-31-16 | Dec-31-15 | Dec-31-14 | Dec-31-13 |
| | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K |
| Revenue | 332.9 | 357.2 | 322.8 | 281.1 | 327.0 | 418.1 | 276.2 |
| Revenue growth | -6.8% | 10.7% | 14.8% | -14.0% | -21.8% | 51.4% | |
| Other Income | 5.9 | 5.2 | 7.4 | 3.1 | 0.9 | 9.7 | |
| Total Revenue and Other Income | 332.9 | 357.2 | 322.8 | 281.1 | 327.0 | 418.1 | 276.2 |
| Total Revenue and Other Income growth | -6.8% | 10.7% | 14.8% | -14.0% | -21.8% | 51.4% | |
| Operating and Other Costs | 217.2 | 214.4 | 195.0 | 183.0 | 194.0 | 239.9 | 151.5 |
| Depreciation, Depletion and Amortization | 45.8 | 44.7 | 41.4 | 42.0 | 44.1 | 43.3 | 25.8 |
| Freight Expense | 4.9 | 10.9 | 18.4 | 11.6 | 3.8 | 4.2 | 3.6 |
| Selling, General and Administrative Expenses | 12.9 | 13.9 | 15.7 | 9.9 | 10.9 | 17.1 | 5.7 |
| Interest Expense, Net | -6.6 | -6.2 | -9.3 | -8.7 | -9.6 | -8.7 | |
| Total Costs | 287.4 | 290.6 | 282.3 | 255.3 | 262.5 | 313.2 | 211.9 |
| Net (Loss) Income | 45.6 | 66.6 | 40.5 | 25.9 | 64.5 | 104.9 | 64.3 |
| Less: General Partner Interest in Net (Loss) Income | 0.8 | 1.1 | 0.7 | | | | |
| Limited Partner Interest in Net Income | 44.8 | 65.4 | 34.1 | | | | |
| |
| Net Income Per Limited Partner Unit - Diluted (in dollars per share) | $1.62 | $2.37 | $1.39 | $0.83 | $0.99 | | |
| |
| Limited Partner Units Outstanding - Basic (in shares) | 27.6 | 27.5 | 24.3 | 23.2 | 23.2 | | |
| Limited Partner Units Outstanding - Diluted (in shares) | 27.7 | 27.6 | 24.5 | 23.4 | 23.2 | | |
| Cash Distributions Declared per Unit (in dollars per share) | 0.0 | 0.0 | | | | | |