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Document and Entity Information (USD $)
 12 Months Ended
Dec. 31, 2013
Feb. 14, 2014
Jun. 30, 2013
Document and entity information [Abstract]      
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     $ 4,892,599,006
Entity Common Stock, Shares Outstanding   189,370,016  
Document Fiscal Year Focus 2013    
Document Fiscal Period Focus FY    
Document Type 10-K    
Amendment Flag false    
Document Period End Date Dec. 31, 2013