XML 84 R126.htm IDEA: XBRL DOCUMENT
v3.19.3.a.u2

Nonqualified Benefit Plans Investments (Details 6) - Supplemental Employee Retirement Plan - Unfunded Plan - USD ($) $ in Thousands | Dec. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |
Investments in nonqualified benefit plans | $ 134,118 | $ 121,930
Equity Securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Investments in nonqualified benefit plans | 87,009 | 73,838
Life insurance carried on plan participants |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Investments in nonqualified benefit plans | 38,659 | 37,274
Other Investments |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Investments in nonqualified benefit plans | $ 8,450 | $ 10,818

X
- Definition Investments in nonqualified benefit plans + References No definition available. + Details
Name: | mdu_InvestmentsInNonqualifiedBenefitPlans
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

X
- Details
Name: | us-gaap_RetirementPlanTypeAxis=us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanFundingStatusAxis=us-gaap_UnfundedPlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_EquitySecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=mdu_LifeInsuranceCarriedOnPlanParticipantsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_OtherInvestmentsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |