Debt (Tables)

12 Months Ended

Dec. 31, 2016

Debt Disclosure [Abstract]

Outstanding 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, 2016			Amount Outstanding at December 31,  2015			Letters of Credit at December 31, 2016			Expiration Date
			(In millions)
MDU Resources Group, Inc.	Commercial paper/Revolving credit agreement	(a)	$	175.0		$	111.0	(b)	$	44.5	(b)	$	—		5/8/19
Cascade Natural Gas Corporation	Revolving credit agreement		$	50.0	(c)	$	—		$	—		$	2.2	(d)	7/9/18
Intermountain Gas Company	Revolving credit agreement		$	65.0	(e)	$	20.9		$	47.9		$	—		7/13/18
Centennial Energy Holdings, Inc.	Commercial paper/Revolving credit agreement	(f)	$	500.0		$	151.0	(b)	$	18.0	(b)	$	—		9/23/21

(a) The commercial paper program is supported by a revolving credit agreement with various banks (provisions allow for increased borrowings, at the option of the Company on stated conditions, up to a maximum of $225.0 million). There were no amounts outstanding under the credit agreement.

(b) Amount outstanding under commercial paper program.

(c) Certain provisions allow for increased borrowings, up to a maximum of $75.0 million.

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

(e) Certain provisions allow for increased borrowings, up to a maximum of $90.0 million.

(f) 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 $600.0 million). There were no amounts outstanding under the credit agreement.

Long term debt outstanding

Long-term debt outstanding at December 31 was as follows:

	2016			2015
	(In thousands)
Senior Notes at a weighted average rate of 4.87%, due on dates ranging from August 31, 2017 to January 15, 2055	$	1,437,831		$	1,616,246
Commercial paper at a weighted average rate of 1.27%, supported by revolving credit agreements	262,000			62,500
Medium-Term Notes at a weighted average rate of 6.68%, due on dates ranging from September 1, 2020 to March 16, 2029	50,000			50,000
Other notes at a weighted average rate of 5.25%, due on February 1, 2035	24,471			24,589
Credit agreements at a weighted average rate of 3.14%, due on dates ranging from July 13, 2018 to November 30, 2038	21,793			48,906
Unamortized debt issuance costs	(5,832		)	(6,069		)
Discount	(104		)	(9		)
Total long-term debt	1,790,159			1,796,163
Less current maturities	43,598			238,539
Net long-term debt	$	1,746,561		$	1,557,624

Schedule of debt maturities

Schedule of Debt Maturities Long-term debt maturities for the five years and thereafter following December 31, 2016, were as follows:

	2017		2018		2019		2020		2021		Thereafter
	(In thousands)
Long-term debt maturities	$	43,598	$	169,449	$	162,154	$	15,021	$	151,013	$	1,254,860