Debt - Short-Term Debt (Details) - USD ($)			1 Months Ended			12 Months Ended
	Jan. 19, 2024	Dec. 05, 2023	May 31, 2023	Apr. 30, 2023	Mar. 31, 2023	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Jan. 20, 2023
Short-term Debt [Line Items]
Short-term borrowings						$ 0	$ 95,000,000
Repayment of short-term borrowings						$ 95,000,000	433,901,000	$ 0
MDU Resources Group, Inc. | Revolving Credit Facility
Short-term Debt [Line Items]
Short-term borrowings			$ 150,000,000				$ 0
Term Loan Agreement | Cascade Natural Gas
Short-term Debt [Line Items]
Short-term borrowings									$ 150,000,000
Repayment of short-term borrowings	$ 50,000,000	$ 100,000,000
Term Loan Agreement | Intermountain Gas Company
Short-term Debt [Line Items]
Short-term borrowings									$ 125,000,000
Repayment of short-term borrowings	$ 45,000,000		$ 30,000,000	$ 30,000,000	$ 20,000,000