Document And Entity Information - shares	9 Months Ended
	Sep. 30, 2017	Oct. 27, 2017
Entity Information [Line Items]
Entity registrant name	MDU RESOURCES GROUP INC
Entity central index key	0000067716
Current fiscal year end date	--12-31
Entity filer category	Large Accelerated Filer
Document type	10-Q
Document period end date	Sep. 30, 2017
Document fiscal year focus	2017
Document fiscal period focus	Q3
Amendment flag	false
Entity common stock, shares outstanding		195,304,376