Document And Entity Information	3 Months Ended
	Mar. 31, 2015	May 01, 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		194,770,955
Document fiscal year focus	2015
Document fiscal period focus	Q1
Document type	10-Q
Amendment flag	false
Document period end date	Mar. 31, 2015