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Percentage of assets sold (Details) | Nov. 21, 2016
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Pronghorn assets held for sale [Member] |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |
Percent of ownership to sell | 50.00%

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- Definition Percent of ownership to sell. + References No definition available. + Details
Name: | mdu_PercentofOwnershipToSell
Namespace Prefix: | mdu_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_DisposalGroupClassificationAxis=mdu_PronghornAssetsHeldforSaleMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |