Debt (Tables)

12 Months Ended

Dec. 31, 2024

Debt Disclosure [Abstract]

Schedule of Line of Credit Facilities

The following table summarizes the outstanding revolving credit facilities of the Company and its subsidiaries:

Company	Facility	Facility Limit			Amount Outstanding at December 31, 2024		Amount Outstanding at December 31, 2023		Letters of Credit at December 31, 2024			Expiration Date
		(In millions)
Montana-Dakota Utilities Co.	Commercial paper/Revolving credit agreement (a)	$	200.0		$	81.4	$	144.2	$	—		10/18/28
Cascade Natural Gas Corporation	Revolving credit agreement	$	175.0	(b)	$	64.6	$	15.4	$	2.2	(c)	6/20/29
Intermountain Gas Company	Revolving credit agreement	$	175.0	(b)	$	105.1	$	30.7	$	—		6/20/29
MDU Resources Group, Inc.	Revolving credit agreement	$	200.0	(d)	$	—	$	—	$	12.1	(c)	5/31/28

(a)The commercial paper program is supported by a revolving credit agreement with various banks (provisions allow for increased borrowings, at the option of Montana-Dakota on stated conditions, up to a maximum of $250.0 million). At December 31, 2024 and 2023, there were no amounts outstanding under the revolving credit agreement.

(b)Certain provisions allow for increased borrowings, up to a maximum of $225.0 million.

(c)Outstanding letter(s) of credit reduce the amount available under the credit agreement.

(d)Certain provisions allow for increased borrowings, up to a maximum of $250.0 million.

Schedule of Long-Term Debt

Long-term debt outstanding was as follows:

	Weighted Average Interest Rate at December 31, 2024		2024		2023
			(In thousands)
Senior notes due on dates ranging from August 23, 2025 to June 15, 2062	4.57	%	$	1,947,000	$	1,882,000
Credit agreements due on June 20, 2029	5.79	%	169,700		46,100
Commercial paper supported by revolving credit agreement	4.76	%	81,400		144,200
Term loan agreements due on dates ranging from September 3, 2032 to April 1, 2039	4.44	%	65,600		64,300
Medium-term notes due on dates ranging from September 15, 2027 to March 16, 2029	7.32	%	35,000		35,000
Other notes due on dates ranging from May 31, 2028 to November 30, 2038	6.00	%	346		980
Less unamortized debt issuance costs			6,436		6,357
Total long-term debt			2,292,610		2,166,223
Less current maturities			161,700		61,319
Net long-term debt			$	2,130,910	$	2,104,904

Schedule of Maturities of Long-Term Debt

Long-term debt maturities, which excludes unamortized debt issuance costs and discount, for the five years and thereafter following December 31, 2024, were as follows:

	2025		2026		2027		2028		2029		Thereafter
	(In thousands)
Long-term debt maturities	$	161,700	$	144,700	$	24,700	$	161,100	$	244,400	$	1,562,446