Condensed Statements of Income and Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Financial Statements, Captions [Line Items]
Operating revenues	$ 1,378,213	$ 1,563,799	$ 1,303,573	$ 1,091,191	$ 1,209,875	$ 1,280,787	$ 1,064,597	$ 976,293	$ 5,336,776	$ 4,531,552	$ 4,443,351
Operating expenses	1,247,992	1,374,329	1,206,262	1,026,973	1,091,524	1,140,783	990,605	906,917	4,855,556	4,129,829	4,019,303
Operating income	130,221	189,470	97,311	64,218	118,351	140,004	73,992	69,376	481,220	401,723	424,048
Other income									15,812	(238)	8,767
Interest expense									98,587	84,614	82,788
Income before income taxes									398,445	316,871	350,027
Income taxes									63,279	47,485	65,041
Net income from continuing operations	$ 94,804	$ 136,128	$ 63,145	$ 41,089	$ 75,982	$ 107,369	$ 44,075	$ 41,960	335,166	269,386	284,986
Loss on redemption of preferred stock									0	0	600
Earnings on common stock									335,453	272,318	280,432
Comprehensive income									331,693	279,269	279,602
MDU Resources Group, Inc. [Member]
Condensed Financial Statements, Captions [Line Items]
Operating revenues									0	628,331	623,693
Operating expenses									0	540,125	520,069
Operating income									0	88,206	103,624
Other income									0	1,504	4,876
Interest expense									0	32,761	31,997
Income before income taxes									0	56,949	76,503
Income taxes									0	(4,259)	13,800
Equity in earnings of subsidiaries from continuing operations									335,166	208,177	222,283
Net income from continuing operations									335,166	269,385	284,986
Equity in earnings (loss) of subsidiaries from discontinued operations									287	2,933	(3,783)
Loss on redemption of preferred stock											600
Dividends declared on preferred stock											171
Earnings on common stock									335,453	272,318	280,432
Comprehensive income									$ 331,693	$ 279,269	$ 279,602