Notes to Condensed Financial Statements (Details 4) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Condensed Financial Statements, Captions [Line Items]
2014	$ 12,300,000
2015	269,400,000
2016	293,800,000
2017	204,900,000
2018	130,200,000
Thereafter	944,000,000
MDU Resources Group, Inc. [Member]
Condensed Financial Statements, Captions [Line Items]
Long-term debt	434,700,000
2014	100,000
2015	100,000
2016	50,100,000
2017	79,000,000
2018	100,000,000
Thereafter	205,400,000
Cash dividends paid to parent company by consolidated subsidiaries	$ 77,600,000	$ 125,800,000	$ 96,100,000