Document And Entity Information - shares	6 Months Ended
	Jun. 30, 2018	Jul. 27, 2018
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	Jun. 30, 2018
Document fiscal year focus	2018
Document fiscal period focus	Q2
Amendment flag	false
Entity common stock, shares outstanding		196,018,324