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Long-term debt outstanding (Details 2) - USD ($) $ in Thousands |  | 9 Months Ended |  |
--- | --- | --- | --- | ---
Jun. 09, 2023 | Sep. 30, 2023 | Sep. 30, 2022 | May 31, 2023 | Dec. 31, 2022
Long-term debt outstanding [Line Items] |  |  |  |  |
Repayments of Long-term Debt |  | $ 434,994 | $ 0 |  |
Long-term debt |  | 2,341,147 | 2,278,730 |  | $ 2,365,667
Long-term debt due within one year |  | 61,319 | 86,319 |  | 47,819
Long-term debt |  | 2,279,828 | 2,192,411 |  | 2,317,848
Long-term Debt |  |  |  |  |
Long-term debt outstanding [Line Items] |  |  |  |  |
Unamortized Debt Issuance Costs |  | 6,637 | 5,295 |  | 5,211
Discount |  | 0 | 444 |  | 286
Long-term Debt | Centennial Energy Holdings, Inc. |  |  |  |  |
Long-term debt outstanding [Line Items] |  |  |  |  |
Repayments of Long-term Debt | $ 455,000 |  |  |  |
Revolving Credit Facility | MDU Resources Group, Inc. |  |  |  |  |
Long-term debt outstanding [Line Items] |  |  |  |  |
Long-term debt |  |  |  | $ 200,000 |
Ratio of total debt to total capitalization as specified in debt covenants |  |  |  | 65.00% |
Term Loan Agreement | MDU Resources Group, Inc. |  |  |  |  |
Long-term debt outstanding [Line Items] |  |  |  |  |
Long-term debt |  |  |  | $ 375,000 |
Ratio of total debt to total capitalization as specified in debt covenants |  |  |  | 65.00% |
Senior Notes |  |  |  |  |
Long-term debt outstanding [Line Items] |  |  |  |  |
Long-term debt |  | $ 1,757,000 | 1,847,000 |  | 1,848,500
Weighted Average Interest Rate |  | 4.33% |  |  |
Term Loan Agreements |  |  |  |  |
Long-term debt outstanding [Line Items] |  |  |  |  |
Long-term debt |  | $ 381,300 | 7,000 |  | 7,000
Weighted Average Interest Rate |  | 6.52% |  |  |
Commercial Paper |  |  |  |  |
Long-term debt outstanding [Line Items] |  |  |  |  |
Long-term debt |  | $ 97,700 | 268,272 |  | 349,050
Weighted Average Interest Rate |  | 5.80% |  |  |
Medium-term Notes |  |  |  |  |
Long-term debt outstanding [Line Items] |  |  |  |  |
Long-term debt |  | $ 35,000 | 35,000 |  | 35,000
Weighted Average Interest Rate |  | 7.32% |  |  |
Credit Agreements |  |  |  |  |
Long-term debt outstanding [Line Items] |  |  |  |  |
Long-term debt |  | $ 38,900 | 125,580 |  | 130,000
Weighted Average Interest Rate |  | 8.50% |  |  |
Other Notes |  |  |  |  |
Long-term debt outstanding [Line Items] |  |  |  |  |
Long-term debt |  | $ 37,884 | $ 1,617 |  | $ 1,614
Weighted Average Interest Rate |  | 8.41% |  |  |

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