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Debt - Long-Term Debt (Details) - USD ($) $ in Thousands | Jun. 30, 2024 | Jun. 20, 2024 | Jun. 19, 2024 | Apr. 01, 2024 | Dec. 31, 2023 | Jun. 30, 2023
--- | --- | --- | --- | --- | --- | ---
Long-term debt outstanding [Line Items] |  |  |  |  |  |
Long-term debt | $ 2,400,617 |  |  |  | $ 2,298,223 | $ 2,247,422
Revolving Credit Facility | Cascade Natural Gas |  |  |  |  |  |
Long-term debt outstanding [Line Items] |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity |  | $ 175,000 | $ 100,000 |  |  |
Ratio of total debt to total capitalization |  | 65.00% |  |  |  |
Revolving Credit Facility | Intermountain Gas Company |  |  |  |  |  |
Long-term debt outstanding [Line Items] |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity |  | $ 175,000 | $ 100,000 |  |  |
Ratio of total debt to total capitalization |  | 65.00% |  |  |  |
Term Loan Agreement | WBI Energy Transmission |  |  |  |  |  |
Long-term debt outstanding [Line Items] |  |  |  |  |  |
Ratio of total debt to total capitalization |  |  |  | 65.00% |  |
Long-term debt |  |  |  | $ 60,000 |  |
Interest rate, stated percentage |  |  |  | 4.52% |  |
Debt instrument, annual principal payment |  |  |  | $ 4,000 |  |

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