Debt (Tables)

12 Months Ended

Dec. 31, 2020

Debt Disclosure [Abstract]

Outstanding credit facilities

The following table summarizes the outstanding revolving credit facilities of the Company's subsidiaries:

Company	Facility	Facility Limit			Amount Outstanding at December 31, 2020		Amount Outstanding at December 31,  2019		Letters of Credit at December 31, 2020			Expiration Date
		(In millions)
Montana-Dakota Utilities Co.	Commercial paper/Revolving credit agreement (a)	$	175.0		$	87.7	$	118.6	$	—		12/19/24
Cascade Natural Gas Corporation	Revolving credit agreement	$	100.0	(b)	$	54.0	$	64.6	$	2.2	(c)	6/7/24
Intermountain Gas Company	Revolving credit agreement	$	85.0	(d)	$	41.9	$	24.5	$	—		6/7/24
Centennial Energy Holdings, Inc.	Commercial paper/Revolving credit agreement (e)	$	600.0		$	37.9	$	104.3	$	—		12/19/24

(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 $225.0 million). There were no amounts outstanding under the revolving credit agreement.

(b)    Certain provisions allow for increased borrowings, up to a maximum of $125.0 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 $110.0 million.

(e)    The commercial paper program is supported by a revolving credit agreement with various banks (provisions allow for increased borrowings, at the option of Centennial on stated conditions, up to a maximum of $700.0 million). There were no amounts outstanding under the revolving credit agreement.

Long term debt outstanding

Long-term debt outstanding was as follows:

	Weighted Average Interest Rate at December 31, 2020		2020		2019
			(In thousands)
Senior Notes due on dates ranging from October 22, 2022 to October 30, 2060	4.40	%	$	1,950,000	$	1,850,000
Commercial paper supported by revolving credit agreements	.28	%	125,600		222,900
Credit agreements due on June 7, 2024	1.88	%	95,900		89,050
Medium-Term Notes due on dates ranging from September 15, 2027 to March 16, 2029	7.32	%	35,000		50,000
Term Loan Agreement due on September 3, 2032	2.00	%	8,400		9,100
Other notes due on dates ranging from July 15, 2021 to November 30, 2038	.75	%	4,034		29,117
Less unamortized debt issuance costs			5,803		7,010
Less discount			1		50
Total long-term debt			2,213,130		2,243,107
Less current maturities			1,555		16,540
Net long-term debt			$	2,211,575	$	2,226,567

Schedule of debt maturities

Long-term debt maturities, which excludes unamortized debt issuance costs and discount, for the five years and thereafter following December 31, 2020, were as follows:

	2021		2022		2023		2024		2025		Thereafter
	(In thousands)
Long-term debt maturities	$	1,555	$	148,021	$	77,921	$	282,922	$	177,802	$	1,530,713