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v3.19.3.a.u2

Goodwill (Details 4) | 3 Months Ended
--- | ---
Dec. 31, 2019
Risk adjusted capital cost | Minimum |
Goodwill [Line Items] |
Rates used to value goodwill | 4.00%
Risk adjusted capital cost | Maximum |
Goodwill [Line Items] |
Rates used to value goodwill | 9.00%
Long-term growth rate | Minimum |
Goodwill [Line Items] |
Rates used to value goodwill | 2.00%
Long-term growth rate | Maximum |
Goodwill [Line Items] |
Rates used to value goodwill | 3.00%

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- Definition Rates used to value goodwill. + References No definition available. + Details
Name: | mdu_RatesUsedtoValueGoodwill
Namespace Prefix: | mdu_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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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_GoodwillLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |