Debt - Long-Term Debt (Details) $ in Thousands			12 Months Ended
	Nov. 15, 2023 USD ($)	Jun. 09, 2023 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Nov. 29, 2023 USD ($)	Oct. 18, 2023 USD ($)	May 31, 2023 USD ($)
Long-term debt outstanding [Line Items]
Long-term debt			$ 2,298,223	$ 2,365,667
Repayments of long-term debt			$ 792,998	65,764	$ 24,758
Montana-Dakota Utilities Co.
Long-term debt outstanding [Line Items]
Ratio of total debt to total capitalization			0.51
Revolving Credit Facility | Montana-Dakota Utilities Co.
Long-term debt outstanding [Line Items]
Line of credit facility, maximum borrowing capacity							$ 200,000
Ratio of funded debt to total capitalization as specified in debt covenants			0.65
Revolving Credit Facility | Cascade Natural Gas
Long-term debt outstanding [Line Items]
Ratio of total debt to total capitalization			0.65
Revolving Credit Facility | Intermountain Gas Company
Long-term debt outstanding [Line Items]
Ratio of total debt to total capitalization			0.65
Revolving Credit Facility | MDU Resources Group, Inc.
Long-term debt outstanding [Line Items]
Ratio of total debt to total capitalization			0.65
Long-term debt								$ 200,000
Senior Notes
Long-term debt outstanding [Line Items]
Long-term debt, gross			$ 1,882,000	$ 1,848,500
Senior Notes | Cascade Natural Gas
Long-term debt outstanding [Line Items]
Ratio of total debt to total capitalization			0.65
Long-term debt						$ 100,000
Interest rate, stated percentage						6.39%
Total debt to total capitalization			0.54
Senior Notes | Intermountain Gas Company
Long-term debt outstanding [Line Items]
Ratio of total debt to total capitalization			0.65
Long-term debt						$ 25,000
Interest rate, stated percentage						6.19%
Total debt to total capitalization			0.57
Senior Notes | Centennial Energy Holdings, Inc.
Long-term debt outstanding [Line Items]
Repayments of long-term debt		$ 455,000
Term Loan Agreement | MDU Resources Group, Inc.
Long-term debt outstanding [Line Items]
Ratio of total debt to total capitalization			65
Long-term debt								$ 375,000
Repayments of long-term debt	$ 185,000
Uncommitted Note Purchase And Private Shelf Agreement | WBI Energy Transmission
Long-term debt outstanding [Line Items]
Line of credit facility, maximum borrowing capacity			$ 350,000
Ratio of total debt to total capitalization			0.55
Total debt to total capitalization			0.41
Long-term debt, gross			$ 235,000
Line of credit facility, remaining borrowing capacity			$ 115,000