| In millions, except per share items | Dec-31-22 | Dec-31-21 | Dec-31-20 | Dec-31-19 | Dec-31-18 | Dec-31-17 | Dec-31-16 | Dec-31-15 |
| | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K |
| Revenue: | | | | | | | | |
| Revenue | | | | | | | | |
| Leasing revenue | 39.2 | 27.1 | 18.8 | 15.6 | | | | |
| Total revenue | 252.3 | 267.0 | 160.6 | 127.1 | 110.3 | 100.0 | 96.9 | 103.9 |
| Total revenue growth | -5.5% | 66.3% | 26.3% | 15.2% | 10.2% | 3.3% | -6.7% | -85.2% |
| Expenses: | | | | | | | | |
| Cost of revenue | 145.9 | 131.3 | 77.8 | | | | | |
| Corporate and other operating expenses | 22.1 | 23.0 | 22.9 | 21.4 | 20.6 | 20.4 | 23.0 | 33.4 |
| Depreciation, depletion and amortization | 22.9 | 18.2 | 12.8 | 10.3 | 9.0 | 8.9 | 8.6 | 9.5 |
| Total expenses | 190.9 | 172.5 | 113.5 | 95.8 | 80.9 | 96.5 | 93.8 | 146.2 |
| Operating income (loss) | 61.5 | 94.5 | 47.1 | 31.3 | 29.4 | 3.6 | 3.1 | -6.1 |
| Operating margin | 24.4% | 35.4% | 29.3% | 24.6% | 26.7% | 3.6% | 3.2% | -5.9% |
| |
| Other income (expense): | | | | | | | | |
| Investment income, net | 9.9 | 7.3 | 5.0 | 10.7 | 12.2 | 35.4 | 17.8 | 22.7 |
| Interest expense | -18.4 | -15.9 | -13.6 | -12.3 | -11.8 | -12.1 | -12.3 | -11.4 |
| Equity in income (loss) from unconsolidated joint ventures | 26.0 | -0.9 | -0.7 | -0.1 | | | | |
| Other income, net | 12.9 | 10.2 | 1.3 | 4.1 | 1.2 | 4.7 | 1.5 | -6.3 |
| Total other income, net | 33.2 | 14.5 | 12.1 | 4.9 | 1.5 | 37.8 | 19.5 | -1.3 |
| Income tax expense | -24.4 | -25.0 | -13.7 | -9.4 | 0.7 | 17.9 | -7.1 | -0.8 |
| Net income | 70.2 | 73.7 | 45.5 | 26.7 | 31.6 | 59.2 | 15.5 | -2.0 |
| Net loss (income) attributable to non-controlling interest | 0.7 | 0.8 | -0.3 | 0.1 | 0.8 | 0.3 | 0.4 | 0.2 |
| Net income attributable to the Company | 70.9 | 74.6 | 45.2 | 26.8 | 32.4 | 59.6 | 15.9 | -1.7 |
| |
| NET INCOME (LOSS) PER SHARE | | | | | | | | |
| NET INCOME PER SHARE ATTRIBUTABLE TO THE COMPANY | | | | | | | | |
| Basic (in dollars per share) | $1.21 | $1.27 | $0.77 | $0.45 | $0.52 | $0.84 | $0.21 | ($0.02) |
| Diluted (in dollars per share) | $1.21 | $1.27 | $0.77 | $0.45 | $0.52 | $0.84 | $0.21 | ($0.02) |
| |
| WEIGHTED AVERAGE SHARES OUTSTANDING | | | | | | | | |
| Basic (in shares) | 58.7 | 58.9 | 59.0 | 60.0 | 62.7 | 70.5 | 74.5 | 87.8 |
| Diluted (in shares) | 58.7 | 58.9 | 59.0 | 60.0 | 62.7 | 70.5 | 74.5 | 87.8 |