Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Feb. 15, 2018	Jun. 30, 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 well-known seasoned issuer	Yes
Entity voluntary filers	No
Entity current reporting status	Yes
Entity filer category	Large Accelerated Filer
Entity public float			$ 5,116,974,651
Entity common stock, shares outstanding		195,304,376
Document fiscal year focus	2017
Document fiscal period focus	FY
Document type	10-K
Amendment flag	false
Document period end date	Dec. 31, 2017