| In millions, except per share items | Jun-30-23 | Mar-31-23 | Dec-31-22 | Sep-30-22 | Jun-30-22 | Mar-31-22 | Dec-31-21 | Sep-30-21 |
| | 10-Q | 10-Q | 8-K | 10-Q | 10-Q | 10-Q | 10-K | 10-Q |
| Operating revenues: | | | | | | | | |
| Regulated operations revenues | 487.9 | 950.0 | | 367.1 | 440.0 | 743.5 | 451.2 | 255.8 |
| Utility infrastructure services revenues | 805.8 | 653.3 | | 758.5 | 706.1 | 523.9 | 633.2 | 632.8 |
| Total operating revenues | 1,293.6 | 1,603.3 | 138.1 | 1,125.6 | 1,146.1 | 1,267.4 | 429.6 | 888.7 |
| Total operating revenues growth | 12.9% | 26.5% | -67.9% | 26.7% | 39.5% | 43.1% | 15.4% | 337.6% |
| Operating expenses: | | | | | | | | |
| Net cost of gas sold | 231.1 | 507.5 | | 101.0 | 147.9 | 298.9 | 134.7 | 63.7 |
| Operations and maintenance | 128.8 | 148.9 | | 154.2 | 175.8 | 149.3 | 138.7 | 122.9 |
| Depreciation and amortization | 111.7 | 112.5 | | 116.9 | 108.0 | 122.6 | 103.4 | 91.4 |
| Taxes other than income taxes | 21.6 | 24.2 | 20.8 | 23.4 | 22.6 | 24.8 | 20.2 | 20.1 |
| Utility infrastructure services expenses | 715.7 | 603.7 | | 680.1 | 646.2 | 503.2 | 573.9 | 567.3 |
| Goodwill impairment and loss on sale | | 71.2 | | | | | | |
| Total operating expenses | 1,208.9 | 1,468.1 | 20.8 | 1,075.7 | 1,100.5 | 1,098.9 | 970.9 | 865.4 |
| Operating income (loss) | 84.8 | 135.2 | 117.3 | 49.9 | 45.7 | 168.5 | 113.5 | 23.3 |
| Operating margin | 6.6% | 8.4% | 85.0% | 4.4% | 4.0% | 13.3% | 26.4% | 2.6% |
| |
| Other income and (expenses): | | | | | | | | |
| Net interest deductions | -69.3 | -77.3 | | -64.4 | -53.2 | -48.4 | -38.0 | -31.3 |
| Other income (deductions) | 19.6 | 18.5 | | 1.6 | -2.8 | 1.2 | 0.5 | -3.1 |
| Total other income and (expenses) | -49.7 | -58.9 | | -62.8 | -56.0 | -47.1 | -37.5 | -34.4 |
| Income (loss) before income taxes | 35.0 | 76.3 | | -12.8 | -10.4 | 121.4 | 76.0 | -11.1 |
| Income tax expense (benefit) | 4.8 | 28.7 | | -1.5 | -4.3 | 24.1 | 4.8 | -1.8 |
| Net income (loss) | 30.3 | 47.7 | -280.6 | -11.3 | -6.1 | 97.3 | 71.2 | -9.3 |
| Net income attributable to noncontrolling interests | 1.4 | 1.7 | | 1.0 | 0.5 | 1.1 | 1.2 | 2.3 |
| Net income (loss) attributable to Southwest Gas Holdings, Inc. | 28.9 | 45.9 | | -12.3 | -6.6 | 96.2 | 69.9 | -11.6 |
| |
| Earnings (loss) per share: | | | | | | | | |
| Basic (in USD per share) | $0.40 | $0.67 | | ($0.18) | ($0.10) | $1.58 | $1.16 | ($0.19) |
| Diluted (in USD per share) | $0.40 | $0.67 | | ($0.18) | ($0.10) | $1.58 | $1.16 | ($0.19) |
| |
| Weighted average shares: | | | | | | | | |
| Basic (in shares) | 71.5 | 68.3 | 67.2 | 67.2 | 67.0 | 60.7 | 59.1 | 59.7 |
| Diluted (in shares) | 71.7 | 68.4 | 67.2 | 67.3 | 67.0 | 60.9 | 59.3 | 59.8 |