Notes to Condensed Financial Statements (Details 4) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Financial Statements, Captions [Line Items]
2015	$ 269,400,000
2016	293,800,000
2017	51,000,000
2018	148,200,000
2019	345,700,000
Thereafter	986,600,000
MDU Resources Group, Inc. [Member]
Condensed Financial Statements, Captions [Line Items]
Long-term debt	508,300,000
2015	100,000
2016	50,100,000
2017	100,000
2018	100,000,000
2019	77,500,000
Thereafter	280,500,000
Cash dividends paid to parent company by consolidated subsidiaries	$ 105,600,000	$ 77,600,000	$ 125,800,000

This element represents disclosure of the aggregate cash dividends paid to the entity by consolidated subsidiaries.

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