Schedule I - Condensed Financial Information of Registrant - Notes to Condensed Financial Statements (Details)			12 Months Ended
	Nov. 01, 2024 USD ($)	Nov. 15, 2023 USD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	May 31, 2023 USD ($)
Condensed Financial Statements, Captions [Line Items]
Short-term borrowings			$ 0	$ 95,000,000
Long-term debt			2,292,610,000	2,166,223,000
Repayments of long-term debt			182,135,000	568,883,000	$ 38,764,000
Repayment of short-term borrowings			95,000,000	433,901,000	0
Long-term debt, maturities year two			$ 144,700,000
MDU Resources Group, Inc. | Term Loan Agreement
Condensed Financial Statements, Captions [Line Items]
Long-term debt						$ 375,000,000
Repayments of long-term debt	$ 190,000,000	$ 185,000,000
MDU Resources Group, Inc. | Revolving Credit Facility
Condensed Financial Statements, Captions [Line Items]
Ratio of total debt to total capitalization			0.65
Long-term debt						200,000,000
MDU Resources Group, Inc. | Revolving Credit Facility
Condensed Financial Statements, Captions [Line Items]
Short-term borrowings				0		$ 150,000,000
MDU Resources Group, Inc.
Condensed Financial Statements, Captions [Line Items]
Repayments of long-term debt			$ 58,000,000	385,000,000	0
Repayment of short-term borrowings			0	242,401,000	0
Long-term debt, maturities year two			0
Cash dividends paid to parent company by consolidated subsidiaries			$ 418,300,000	$ 165,500,000	$ 242,100,000