Condensed Statements of Income and Comprehensive Income (Details 2) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Financial Statements, Captions [Line Items]
Operating revenues	$ 1,016,099	$ 1,208,567	$ 1,043,948	$ 860,214	$ 1,016,826	$ 1,198,342	$ 938,039	$ 860,845	$ 4,128,828	$ 4,014,052	$ 4,115,073
Operating expenses	904,613	1,061,883	954,983	798,229	934,896	1,070,514	878,330	810,537	3,719,708	3,694,277	3,787,891
Operating income	$ 111,486	$ 146,684	$ 88,965	$ 61,985	$ 81,930	$ 127,828	$ 59,709	$ 50,308	409,120	319,775	327,182
Other income									4,956	18,457	9,138
Interest expense									87,848	91,179	86,871
Income before income taxes									326,228	247,053	249,449
Income taxes									93,132	70,664	64,422
Earnings (loss) on common stock									63,748	(623,120)	297,548
Comprehensive income (loss)									65,848	(617,480)	294,335
MDU Resources Group, Inc. [Member]
Condensed Financial Statements, Captions [Line Items]
Operating revenues									561,266	556,112	628,578
Operating expenses									469,062	478,198	547,820
Operating income									92,204	77,914	80,758
Other income									1,491	8,318	5,271
Interest expense									31,519	23,562	21,055
Income before income taxes									62,176	62,670	64,974
Income taxes									6,355	15,882	16,819
Equity in earnings of subsidiaries from continuing operations									177,275	129,601	136,872
Net income from continuing operations									233,096	176,389	185,027
Equity in earnings (loss) of subsidiaries from discontinued operations attributable to the company									(168,663)	(798,824)	113,206
Dividends declared on preferred stocks									685	685	685
Earnings (loss) on common stock									63,748	(623,120)	297,548
Comprehensive income (loss)									$ 65,848	$ (617,480)	$ 294,335