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%