| In millions, except per share items | Dec-31-19 | Dec-31-18 | Dec-05-18 | Dec-31-17 | Dec-31-16 | Dec-31-15 | Dec-31-14 | Dec-31-13 |
| | 10-K | 10-K | 8-K | 10-K | 10-K | 10-K | 10-K | 10-K |
| Revenues: | | | | | | | | |
| Total revenues | 490.5 | 300.2 | 300.2 | 154.6 | 67.6 | 79.4 | 55.2 | 44.1 |
| Total revenues growth | 63.4% | 94.1% | | 128.9% | -14.9% | 43.9% | 25.1% | 35.4% |
| Expenses: | | | | | | | | |
| Salaries and related employee expenses | 35.0 | 18.4 | | 3.8 | 1.4 | | | |
| Water service-related expenses | 20.8 | 11.2 | 11.2 | 0.5 | | | | |
| General and administrative expenses | 9.8 | 4.7 | 4.7 | 1.5 | 0.9 | 0.8 | 0.6 | 0.6 |
| Legal and professional fees | 16.4 | 2.5 | 2.5 | 3.5 | 0.8 | 0.7 | 0.5 | 0.8 |
| Depreciation, depletion and amortization | 8.9 | 2.6 | | 0.4 | 0.0 | 0.0 | | |
| Total operating expenses | 90.9 | 39.4 | 78.8 | 9.7 | 4.6 | 4.2 | 3.8 | 4.0 |
| Operating income | 399.6 | 260.8 | 260.8 | 144.9 | 62.9 | 75.3 | 51.4 | 40.1 |
| Operating margin | 81.5% | 86.9% | 86.9% | 93.7% | 93.1% | 94.8% | 93.1% | 91.0% |
| Other income, net | 2.7 | 0.9 | 0.9 | 0.1 | 0.0 | | | |
| Income before income taxes | 402.3 | 261.8 | | 145.1 | 62.9 | 75.3 | 51.4 | 40.1 |
| |
| Income tax expense (benefit): | | | | | | | | |
| Current | 57.5 | 37.2 | 37.2 | 46.9 | 22.0 | 25.4 | 17.6 | 13.7 |
| Deferred | 26.0 | 14.8 | 14.8 | 1.0 | -1.4 | -0.2 | -1.0 | -0.8 |
| Total income tax expense | 83.5 | 52.0 | 52.0 | 47.8 | 20.6 | 25.2 | 16.7 | 12.9 |
| Net income | 318.7 | 209.7 | 209.7 | 97.2 | 42.3 | 50.0 | 34.8 | 27.2 |
| |
| Other comprehensive income — periodic pension costs, net of income taxes of $4, $2, $11 and $7, respectively | | | | | | | | |
| Total comprehensive income | 318.3 | 209.6 | | 97.4 | 42.6 | 50.1 | 34.0 | 27.6 |
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| Weighted average number of Sub-share Certificates outstanding (in shares) | 7.8 | 7.8 | | 7.9 | 8.0 | 8.2 | 8.4 | 8.6 |
| |
| Net income per Sub-share Certificate — basic and diluted (in dollars per share) | $41.09 | $26.93 | | $12.38 | $5.29 | $6.10 | $4.14 | $3.16 |
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