Document And Entity Information - shares	6 Months Ended
	Jun. 30, 2015	Jul. 28, 2015
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
Entity common stock, shares outstanding		195,063,757
Document fiscal year focus	2015
Document fiscal period focus	Q2
Document type	10-Q
Amendment flag	false
Document period end date	Jun. 30, 2015