| In millions, except per share items | Sep-30-18 | Jun-30-18 | Mar-31-18 | Dec-31-17 | Sep-30-17 | Jun-30-17 | Mar-31-17 | Dec-31-16 |
| | 10-Q | 10-Q | 10-Q | 10-K | 10-Q | 10-Q | 10-Q | 10-K |
| Revenue: | | | | | | | | |
| Total revenue | 106.7 | 73.4 | 74.7 | 85.7 | 79.4 | 70.3 | 64.6 | 62.7 |
| Total revenue growth | 34.5% | 4.4% | 15.7% | 36.7% | 67.4% | 98.5% | 239.9% | 119.9% |
| Operating expenses: | | | | | | | | |
| Lease operating | 18.8 | 15.4 | | | 25.1 | 19.9 | | |
| Production and ad valorem taxes | 7.4 | 5.5 | 5.5 | 1.7 | 6.6 | 5.6 | 6.0 | 4.0 |
| Depletion, depreciation and amortization | 33.0 | 23.5 | 23.5 | | 25.5 | 22.3 | 16.0 | |
| General and administrative | 10.2 | 15.9 | 21.1 | 19.1 | 9.5 | 9.5 | 10.4 | 9.0 |
| Cash-settled incentive awards | 11.5 | 0.0 | 11.3 | 7.2 | 5.0 | -1.4 | 5.4 | 16.7 |
| Total operating expenses | 80.9 | 60.2 | 73.2 | 72.1 | 71.7 | 55.8 | 56.2 | 64.0 |
| Income from operations | 25.8 | 13.2 | 1.6 | 13.6 | 7.6 | 14.4 | 8.4 | -1.4 |
| Operating margin | 24.2% | 17.9% | 2.1% | 15.9% | 9.6% | 20.5% | 13.0% | -2.2% |
| |
| Other income (expense): | | | | | | | | |
| Interest expense, net | -10.0 | -26.5 | -7.6 | -8.4 | -8.5 | -23.5 | -17.7 | -11.4 |
| Commodity derivative instruments gain (loss) | -32.6 | -12.1 | -9.4 | -10.2 | -13.7 | 7.5 | 10.8 | -8.0 |
| Contingent payment derivative instrument gain | 2.4 | 3.7 | 2.6 | | | | | |
| Other income (expense) | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.1 | -0.1 | 0.2 |
| Total other expense | -40.1 | -16.9 | -14.4 | -15.2 | -22.3 | -1.2 | -6.9 | -19.2 |
| Income (loss) before income taxes | -14.3 | | -12.9 | -1.6 | -14.6 | | 1.5 | -20.6 |
| Income tax benefit | | | | 0.3 | 0.0 | | | |
| Net income (loss) | -14.3 | -3.7 | -12.9 | -1.3 | -14.6 | 13.2 | 1.5 | -20.6 |
| Preferred stock dividends | -1.3 | -1.3 | -1.3 | -2.5 | | -2.5 | -1.4 | |
| Net loss available to common stockholders | -15.6 | -5.0 | -14.1 | -3.9 | -14.6 | 10.7 | 0.1 | -20.6 |
| |
| Net loss per common share: | | | | | | | | |
| Basic and diluted | ($0.70) | ($0.22) | ($0.64) | ($0.13) | ($0.71) | $0.49 | $0.01 | ($1.00) |
| |
| Weighted average common shares outstanding: | | | | | | | | |
| Basic and diluted | 22.3 | | | 0.0 | 21.9 | | | 0.6 |