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Long-term borrowings (Details 2) - Long-term debt $ in Millions | Dec. 31, 2018 USD ($)
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MDU Resources Group, Inc. | Revolving credit facility |
Debt instrument [Line Items] |
Ratio of funded debt to total capitalization as specified in debt covenants | 65.00%
Ratio of funded debt to capitalization - Company alone, as specified in debt convenants | 65.00%
Ratio of total debt to total capitalization | 45.00%
Cascade Natural Gas Corporation | Revolving credit facility |
Debt instrument [Line Items] |
Ratio of total debt to total capitalization as specified in debt covenants | 65.00%
Ratio of total debt to total capitalization | 51.00%
Intermountain Gas Company | Revolving credit facility |
Debt instrument [Line Items] |
Ratio of total debt to total capitalization as specified in debt covenants | 65.00%
Ratio of total debt to total capitalization | 49.00%
Centennial Energy Holdings, Inc. | Revolving credit facility |
Debt instrument [Line Items] |
Ratio of total debt to total capitalization as specified in debt covenants | 65.00%
Ratio of total debt to total capitalization | 38.00%
WBI Energy Transmission, Inc. | Uncommitted long term private shelf agreement |
Debt instrument [Line Items] |
Long-term private shelf agreement issuance capacity | $ 200.0
Notes outstanding | 140.0
Remaining capacity under uncommitted private shelf agreement | $ 60.0
Ratio of total debt to total capitalization as specified in debt covenants | 55.00%
Ratio of total debt to total capitalization | 40.00%

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