Insurance (Details 11) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012
Maximum amount of deductibles for workers' compensation insurance per occurrence	$ 1
Maximum amount of deductibles for automobile liability and general liability insurance per accident or occurrence	$ 1

Maximum amount of risk retained by the entity before the automobile and general liability insurance arrangement begins to provide coverage.

No definition available.

Name:	mdu_MaximumAmountOfDeductiblesForAutomobileLiabilityAndGeneralLiabilityInsurancePerAccidentOrOccurrence
Namespace Prefix:	mdu_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant