Income Taxes - Additional Information (Detail) - USD ($) $ in Millions |
6 Months Ended | 12 Months Ended | |||
|---|---|---|---|---|---|
Jun. 30, 2026 |
Jun. 30, 2025 |
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2017 |
|
| Income Taxes [Line Items] | |||||
| U.S. Federal Statutory Tax Rate Percent | 21.00% | 21.00% | 21.00% | ||
| Regulatory Liability | $ 99.5 | $ 73.5 | $ 80.8 | ||
| Regulatory liability, expected flow back to customers | $ 47.1 | ||||
| State Taxes Credit to Offset Future Taxes | 1.8 | ||||
| Net Operating Loss Carryforwards Utilized For Income Taxes | $ 5.6 | ||||
| Federal tax credit carryforward | $ 1.0 | ||||
| Gas Ratepayers | Massachusetts And Maine [Member] | |||||
| Income Taxes [Line Items] | |||||
| Regulatory liability, expected flow back to customers | 15.1 | ||||
| Income Tax Related Liabilities | |||||
| Income Taxes [Line Items] | |||||
| Regulatory Liability | $ 53.4 | $ 49.7 | $ 51.1 | $ 48.9 | |