| 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 |
| Operating Revenues | | | | | | | | |
| Total Operating Revenues | 473.3 | 418.6 | 437.3 | 439.4 | 806.4 | 377.3 | 426.8 | 425.8 |
| Total Operating Revenues growth | 13.1% | -4.3% | -0.5% | -45.5% | 113.7% | -11.6% | 0.2% | 16.1% |
| Operating Expenses | | | | | | | | |
| Cost of Sales | | | | | | | | |
| Operation and Maintenance | 68.7 | 65.7 | 67.2 | 69.5 | 64.5 | 61.4 | 67.1 | 64.6 |
| Depreciation and Amortization | 59.5 | 54.5 | 52.0 | 50.4 | 46.9 | 46.6 | 45.7 | 42.1 |
| Taxes Other than Income Taxes | 24.5 | 23.9 | 22.7 | 22.4 | 21.1 | 19.6 | 17.7 | 17.2 |
| Operating Income | 77.8 | 71.4 | 73.1 | 71.2 | 75.4 | 70.2 | 63.1 | 60.0 |
| Operating margin | 16.4% | 17.1% | 16.7% | 16.2% | 9.4% | 18.6% | 14.8% | 14.1% |
| Interest Expense, Net | 25.6 | 23.8 | 23.7 | 24.0 | 23.1 | 22.5 | 21.9 | 20.9 |
| Other Expense (Income), Net | 4.6 | 5.2 | -8.6 | -5.8 | 5.8 | 5.2 | -0.5 | 0.4 |
| Income Before Income Taxes | 47.6 | 42.4 | 58.0 | 41.4 | 46.5 | 42.5 | 41.7 | 38.7 |
| Provision For Income Taxes | 11.5 | 10.2 | 13.8 | 8.4 | 17.5 | 15.4 | 15.4 | 14.0 |
| Net Income | 36.1 | 32.2 | 44.2 | 33.0 | 29.0 | 27.1 | 26.3 | 24.7 |
| |
| Net Income Per Common Share-Basic | $2.35 | $2.15 | $2.97 | $2.23 | $2.06 | $1.94 | $1.89 | $1.79 |
| Net Income Per Common Share-Diluted | $2.35 | $2.15 | $2.97 | $2.23 | $2.06 | $1.94 | $1.89 | $1.79 |
| |
| Weighted Average Common Shares Outstanding-Basic | 15.4 | 15.0 | 14.9 | 14.8 | 14.1 | 14.0 | 13.9 | 13.8 |
| Weighted Average Common Shares Outstanding-Diluted | 15.4 | 15.0 | 14.9 | 14.8 | 14.1 | 14.0 | 13.9 | 13.8 |