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Short-term Debt (Details 1) - USD ($) $ in Thousands |  |  |  | 9 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
May 31, 2023 | Apr. 30, 2023 | Mar. 31, 2023 | Sep. 30, 2023 | Sep. 30, 2022 | May 01, 2023 | Mar. 17, 2023 | Jan. 20, 2023 | Dec. 31, 2022 | Dec. 19, 2022
Short-Term Debt [Line Items] |  |  |  |  |  |  |  |  |  |
Short-term borrowings |  |  |  | $ 306,400 | $ 0 |  |  |  | $ 38,500 |
Repayment of short-term borrowings |  |  |  | 193,500 | $ 0 |  |  |  |  |
Term Loan Agreement | Cascade Natural Gas [Member] |  |  |  |  |  |  |  |  |  |
Short-Term Debt [Line Items] |  |  |  |  |  |  |  |  |  |
Short-term borrowings |  |  |  |  |  |  |  | $ 150,000 |  |
Ratio of total debt to total capitalization as specified in debt covenants |  |  |  |  |  |  |  | 65.00% |  |
Term Loan Agreement | Intermountain Gas Company |  |  |  |  |  |  |  |  |  |
Short-Term Debt [Line Items] |  |  |  |  |  |  |  |  |  |
Short-term borrowings |  |  |  |  |  |  |  | $ 125,000 |  |
Ratio of total debt to total capitalization as specified in debt covenants |  |  |  |  |  |  |  | 65.00% |  |
Repayment of short-term borrowings | $ 30,000 | $ 30,000 | $ 20,000 |  |  |  |  |  |  |
Term Loan Agreement | Centennial Energy Holdings, Inc. |  |  |  |  |  |  |  |  |  |
Short-Term Debt [Line Items] |  |  |  |  |  |  |  |  |  |
Short-term borrowings |  |  |  |  |  |  | $ 100,000 |  |  | $ 135,000
Term Loan Agreement | Centennial Energy Holdings, Inc. | Maximum [Member] |  |  |  |  |  |  |  |  |  |
Short-Term Debt [Line Items] |  |  |  |  |  |  |  |  |  |
Repayment of short-term borrowings | 135,000 |  |  |  |  |  |  |  |  |
Term Loan Agreement | Centennial Energy Holdings, Inc. | Minimum [Member] |  |  |  |  |  |  |  |  |  |
Short-Term Debt [Line Items] |  |  |  |  |  |  |  |  |  |
Repayment of short-term borrowings | 100,000 |  |  |  |  |  |  |  |  |
Term Loan Agreement | MDU Resources Group, Inc. |  |  |  |  |  |  |  |  |  |
Short-Term Debt [Line Items] |  |  |  |  |  |  |  |  |  |
Short-term borrowings |  |  |  |  |  | $ 75,000 |  |  |  |
Repayment of short-term borrowings | 75,000 |  |  |  |  |  |  |  |  |
Revolving Credit Facility | MDU Resources Group, Inc. |  |  |  |  |  |  |  |  |  |
Short-Term Debt [Line Items] |  |  |  |  |  |  |  |  |  |
Short-term borrowings | $ 150,000 |  |  |  |  |  |  |  |  |
Ratio of total debt to total capitalization as specified in debt covenants | 65.00% |  |  |  |  |  |  |  |  |
Revolving Credit Agreement, Amount Outstanding | MDU Resources Group, Inc. |  |  |  |  |  |  |  |  |  |
Short-Term Debt [Line Items] |  |  |  |  |  |  |  |  |  |
Short-term borrowings |  |  |  | $ 111,400 |  |  |  |  |  |

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