XML 152 R125.htm IDEA: XBRL DOCUMENT
v3.22.0.1

Multiemployer Plans Participation by Plan (Details 18) - Pension Benefits - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Multiemployer Plans [Line Items] |  |  |
Multiemployer Plan, Pension, Insignificant, Employer Contribution, Cost | $ 23,390 | $ 23,722 | $ 19,598
Multiemployer Plan, Employer Contribution, Cost | $ 82,388 | $ 85,444 | 72,525
Edison Pension Plan |  |  |
Multiemployer Plans [Line Items] |  |  |
Multiemployer Plan, Pension, Significant, Employer Identification Number | 936061681 |  |
Multiemployer Plan, Pension, Significant, Plan Number | 001 |  |
Multiemployer Plan, Pension, Significant, Certified Zone Status [Fixed List] | Green | Green |
Multiemployer Plan, Pension, Significant, Funding Improvement or Rehabilitation Plan, Implementation Status [Fixed List] | No |  |
Multiemployer Plan, Pension, Significant, Employer Contribution, Cost | $ 18,331 | $ 16,121 | 12,252
Multiemployer Plan, Pension, Significant, Surcharge [Fixed List] | No |  |
Multiemployer Plan, Pension, Significant, Collective-Bargaining Arrangement, Expiration Date | Dec. 31, 2023 |  |
IBEW Local 212 Pension Trust |  |  |
Multiemployer Plans [Line Items] |  |  |
Multiemployer Plan, Pension, Significant, Employer Identification Number | 316127280 |  |
Multiemployer Plan, Pension, Significant, Plan Number | 001 |  |
Multiemployer Plan, Pension, Significant, Certified Zone Status [Fixed List] | Green | Green |
Multiemployer Plan, Pension, Significant, Certified Zone Status, Date | Apr. 30, 2021 | Apr. 30, 2020 |
Multiemployer Plan, Pension, Significant, Funding Improvement or Rehabilitation Plan, Implementation Status [Fixed List] | No |  |
Multiemployer Plan, Pension, Significant, Employer Contribution, Cost | $ 1,733 | $ 1,521 | 1,110
Multiemployer Plan, Pension, Significant, Surcharge [Fixed List] | No |  |
Multiemployer Plan, Pension, Significant, Collective-Bargaining Arrangement, Expiration Date | Jun. 01, 2025 |  |
IBEW Local 357 Pension Plan A |  |  |
Multiemployer Plans [Line Items] |  |  |
Multiemployer Plan, Pension, Significant, Employer Identification Number | 886023284 |  |
Multiemployer Plan, Pension, Significant, Plan Number | 001 |  |
Multiemployer Plan, Pension, Significant, Certified Zone Status [Fixed List] | Green | Green |
Multiemployer Plan, Pension, Significant, Funding Improvement or Rehabilitation Plan, Implementation Status [Fixed List] | No |  |
Multiemployer Plan, Pension, Significant, Employer Contribution, Cost | $ 6,485 | $ 9,913 | 10,162
Multiemployer Plan, Pension, Significant, Surcharge [Fixed List] | No |  |
Multiemployer Plan, Pension, Significant, Collective-Bargaining Arrangement, Expiration Date | May 31, 2024 |  |
IBEW Local 82 Pension Plan |  |  |
Multiemployer Plans [Line Items] |  |  |
Multiemployer Plan, Pension, Significant, Employer Identification Number | 316127268 |  |
Multiemployer Plan, Pension, Significant, Plan Number | 001 |  |
Multiemployer Plan, Pension, Significant, Certified Zone Status [Fixed List] | Green | Green |
Multiemployer Plan, Pension, Significant, Certified Zone Status, Date | Jun. 30, 2021 | Jun. 30, 2020 |
Multiemployer Plan, Pension, Significant, Funding Improvement or Rehabilitation Plan, Implementation Status [Fixed List] | No |  |
Multiemployer Plan, Pension, Significant, Employer Contribution, Cost | $ 1,353 | $ 1,373 | 1,662
Multiemployer Plan, Pension, Significant, Surcharge [Fixed List] | No |  |
Multiemployer Plan, Pension, Significant, Collective-Bargaining Arrangement, Expiration Date | Dec. 03, 2023 |  |
Idaho Plumbers and Pipefitters Pension Plan |  |  |
Multiemployer Plans [Line Items] |  |  |
Multiemployer Plan, Pension, Significant, Employer Identification Number | 826010346 |  |
Multiemployer Plan, Pension, Significant, Plan Number | 001 |  |
Multiemployer Plan, Pension, Significant, Certified Zone Status [Fixed List] | Green | Green |
Multiemployer Plan, Pension, Significant, Certified Zone Status, Date | May 31, 2021 | May 31, 2020 |
Multiemployer Plan, Pension, Significant, Funding Improvement or Rehabilitation Plan, Implementation Status [Fixed List] | No |  |
Multiemployer Plan, Pension, Significant, Employer Contribution, Cost | $ 1,528 | $ 1,370 | 1,307
Multiemployer Plan, Pension, Significant, Surcharge [Fixed List] | No |  |
Multiemployer Plan, Pension, Significant, Collective-Bargaining Arrangement, Expiration Date | Mar. 31, 2023 |  |
National Electrical Benefit Fund |  |  |
Multiemployer Plans [Line Items] |  |  |
Multiemployer Plan, Pension, Significant, Employer Identification Number | 530181657 |  |
Multiemployer Plan, Pension, Significant, Plan Number | 001 |  |
Multiemployer Plan, Pension, Significant, Certified Zone Status [Fixed List] | Green | Green |
Multiemployer Plan, Pension, Significant, Funding Improvement or Rehabilitation Plan, Implementation Status [Fixed List] | No |  |
Multiemployer Plan, Pension, Significant, Employer Contribution, Cost | $ 14,361 | $ 14,484 | 12,679
Multiemployer Plan, Pension, Significant, Surcharge [Fixed List] | No |  |
National Electrical Benefit Fund | Minimum |  |  |
Multiemployer Plans [Line Items] |  |  |
Multiemployer Plan, Pension, Significant, Collective-Bargaining Arrangement, Expiration Date | May 31, 2021 |  |
National Electrical Benefit Fund | Maximum |  |  |
Multiemployer Plans [Line Items] |  |  |
Multiemployer Plan, Pension, Significant, Collective-Bargaining Arrangement, Expiration Date | May 31, 2026 |  |
Pension and Retirement Plan of Plumbers and Pipefitters Local 525 |  |  |
Multiemployer Plans [Line Items] |  |  |
Multiemployer Plan, Pension, Significant, Employer Identification Number | 886003864 |  |
Multiemployer Plan, Pension, Significant, Plan Number | 001 |  |
Multiemployer Plan, Pension, Significant, Certified Zone Status [Fixed List] | Green | Green |
Multiemployer Plan, Pension, Significant, Funding Improvement or Rehabilitation Plan, Implementation Status [Fixed List] | No |  |
Multiemployer Plan, Pension, Significant, Employer Contribution, Cost | $ 4,345 | $ 6,266 | 4,747
Multiemployer Plan, Pension, Significant, Surcharge [Fixed List] | No |  |
Multiemployer Plan, Pension, Significant, Collective-Bargaining Arrangement, Expiration Date | Sep. 30, 2024 |  |
Pension Trust Fund for Operating Engineers |  |  |
Multiemployer Plans [Line Items] |  |  |
Multiemployer Plan, Pension, Significant, Employer Identification Number | 946090764 |  |
Multiemployer Plan, Pension, Significant, Plan Number | 001 |  |
Multiemployer Plan, Pension, Significant, Certified Zone Status [Fixed List] | Yellow | Yellow |
Multiemployer Plan, Pension, Significant, Funding Improvement or Rehabilitation Plan, Implementation Status [Fixed List] | Implemented |  |
Multiemployer Plan, Pension, Significant, Employer Contribution, Cost | $ 2,495 | $ 2,680 | 2,598
Multiemployer Plan, Pension, Significant, Surcharge [Fixed List] | No |  |
Pension Trust Fund for Operating Engineers | Minimum |  |  |
Multiemployer Plans [Line Items] |  |  |
Multiemployer Plan, Pension, Significant, Collective-Bargaining Arrangement, Expiration Date | Jun. 15, 2022 |  |
Pension Trust Fund for Operating Engineers | Maximum |  |  |
Multiemployer Plans [Line Items] |  |  |
Multiemployer Plan, Pension, Significant, Collective-Bargaining Arrangement, Expiration Date | Jun. 30, 2023 |  |
Sheet Metal Workers Pension Plan of Southern CA, AZ, and NV |  |  |
Multiemployer Plans [Line Items] |  |  |
Multiemployer Plan, Pension, Significant, Employer Identification Number | 956052257 |  |
Multiemployer Plan, Pension, Significant, Plan Number | 001 |  |
Multiemployer Plan, Pension, Significant, Certified Zone Status [Fixed List] | Yellow | Yellow |
Multiemployer Plan, Pension, Significant, Funding Improvement or Rehabilitation Plan, Implementation Status [Fixed List] | Implemented |  |
Multiemployer Plan, Pension, Significant, Employer Contribution, Cost | $ 2,615 | $ 3,255 | 2,119
Multiemployer Plan, Pension, Significant, Surcharge [Fixed List] | No |  |
Multiemployer Plan, Pension, Significant, Collective-Bargaining Arrangement, Expiration Date | Jun. 30, 2024 |  |
Southern California IBEW-NECA Pension Trust Fund |  |  |
Multiemployer Plans [Line Items] |  |  |
Multiemployer Plan, Pension, Significant, Employer Identification Number | 956392774 |  |
Multiemployer Plan, Pension, Significant, Plan Number | 001 |  |
Multiemployer Plan, Pension, Significant, Certified Zone Status [Fixed List] | Yellow | Yellow |
Multiemployer Plan, Pension, Significant, Certified Zone Status, Date | Jun. 30, 2021 | Jun. 30, 2020 |
Multiemployer Plan, Pension, Significant, Funding Improvement or Rehabilitation Plan, Implementation Status [Fixed List] | Implemented |  |
Multiemployer Plan, Pension, Significant, Employer Contribution, Cost | $ 2,746 | $ 1,714 | 1,477
Multiemployer Plan, Pension, Significant, Surcharge [Fixed List] | No |  |
Southern California IBEW-NECA Pension Trust Fund | Minimum |  |  |
Multiemployer Plans [Line Items] |  |  |
Multiemployer Plan, Pension, Significant, Collective-Bargaining Arrangement, Expiration Date | Jun. 30, 2022 |  |
Southern California IBEW-NECA Pension Trust Fund | Maximum |  |  |
Multiemployer Plans [Line Items] |  |  |
Multiemployer Plan, Pension, Significant, Collective-Bargaining Arrangement, Expiration Date | May 31, 2026 |  |
Western Conference of Teamsters Pension Plan |  |  |
Multiemployer Plans [Line Items] |  |  |
Multiemployer Plan, Pension, Significant, Employer Identification Number | 916145047 |  |
Multiemployer Plan, Pension, Significant, Plan Number | 001 |  |
Multiemployer Plan, Pension, Significant, Certified Zone Status [Fixed List] | Green | Green |
Multiemployer Plan, Pension, Significant, Funding Improvement or Rehabilitation Plan, Implementation Status [Fixed List] | No |  |
Multiemployer Plan, Pension, Significant, Employer Contribution, Cost | $ 3,006 | $ 3,025 | $ 2,814
Multiemployer Plan, Pension, Significant, Surcharge [Fixed List] | No |  |
Western Conference of Teamsters Pension Plan | Minimum |  |  |
Multiemployer Plans [Line Items] |  |  |
Multiemployer Plan, Pension, Significant, Collective-Bargaining Arrangement, Expiration Date | Dec. 31, 2023 |  |
Western Conference of Teamsters Pension Plan | Maximum |  |  |
Multiemployer Plans [Line Items] |  |  |
Multiemployer Plan, Pension, Significant, Collective-Bargaining Arrangement, Expiration Date | Dec. 31, 2025 |  |

X
- Definition Amount of cost for employer contribution to multiemployer plan. Multiemployer plan includes, but is not limited to, pension plan determined to be individually significant and insignificant and other postretirement benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=35742348&loc=SL14450788-114948 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 35 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=29639808&loc=d3e29008-114946 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450702-114947 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 9 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450691-114947 + Details
Name: | us-gaap_MultiemployerPlanEmployerContributionCost
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of cost for employer contribution to multiemployer pension plan determined to be individually insignificant. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450691-114947 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=35742348&loc=SL14450788-114948 Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 5 -Subparagraph (e)(1) -URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450657-114947 + Details
Name: | us-gaap_MultiemployerPlanPensionInsignificantEmployerContributionCost
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Year-end date of plan applicable to certified zone status for multiemployer pension plan determined to be individually significant, in YYYY-MM-DD format. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=35742348&loc=SL14450788-114948 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 5 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450657-114947 + Details
Name: | us-gaap_MultiemployerPlanPensionSignificantCertifiedZoneStatusDate
Namespace Prefix: | us-gaap_
Data Type: | xbrli:dateItemType
Balance Type: | na
Period Type: | duration

X
- Definition Indicates certified zone status of multiemployer pension plan determined to be individually significant. Acceptable values are "Green", "Yellow", "Orange", "Red", "Other", and "NA". + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=35742348&loc=SL14450788-114948 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 5 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450657-114947 + Details
Name: | us-gaap_MultiemployerPlanPensionSignificantCertifiedZoneStatusFixedList
Namespace Prefix: | us-gaap_
Data Type: | us-types:zoneStatusItemType
Balance Type: | na
Period Type: | duration

X
- Definition Expiration date of collective-bargaining arrangement (CBA) requiring contribution to multiemployer pension plan determined to be individually significant, in YYYY-MM-DD format. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=35742348&loc=SL14450788-114948 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 5 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450657-114947 + Details
Name: | us-gaap_MultiemployerPlanPensionSignificantCollectiveBargainingArrangementExpirationDate
Namespace Prefix: | us-gaap_
Data Type: | xbrli:dateItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of cost for employer contribution to multiemployer pension plan determined to be individually significant. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 5 -Subparagraph (e)(1) -URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450657-114947 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=35742348&loc=SL14450788-114948 + Details
Name: | us-gaap_MultiemployerPlanPensionSignificantEmployerContributionCost
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Employer Identification Number (EIN) or Tax Identification Number (TIN) assigned by Internal Revenue Service (IRS) for multiemployer pension plan determined to be individually significant, in nine-digit numeric format. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 5 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450657-114947 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=35742348&loc=SL14450788-114948 + Details
Name: | us-gaap_MultiemployerPlanPensionSignificantEmployerIdentificationNumber
Namespace Prefix: | us-gaap_
Data Type: | us-types:nineDigitItemType
Balance Type: | na
Period Type: | duration

X
- Definition Indicates whether funding improvement plan or rehabilitation plan was implemented or pending for multiemployer pension plan, determined to be individually significant. Acceptable values are "No", "Pending", "Implemented", "Other", and "NA". + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=35742348&loc=SL14450788-114948 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 5 -Subparagraph (f)(1) -URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450657-114947 + Details
Name: | us-gaap_MultiemployerPlanPensionSignificantFundingImprovementOrRehabilitationPlanImplementationStatusFixedList
Namespace Prefix: | us-gaap_
Data Type: | us-types:fundingImprovementAndRehabilitationPlanItemType
Balance Type: | na
Period Type: | duration

X
- Definition Plan number for multiemployer pension plan determined to be individually significant, in three-digit numeric format. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=35742348&loc=SL14450788-114948 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 5 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450657-114947 + Details
Name: | us-gaap_MultiemployerPlanPensionSignificantPlanNumber
Namespace Prefix: | us-gaap_
Data Type: | us-types:threeDigitItemType
Balance Type: | na
Period Type: | duration

X
- Definition Indicates whether employer paid surcharge to multiemployer pension plan determined to be individually significant. Acceptable values are "No", "Yes" and "NA". + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=35742348&loc=SL14450788-114948 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 5 -Subparagraph (f)(2) -URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450657-114947 + Details
Name: | us-gaap_MultiemployerPlanPensionSignificantSurchargeFixedList
Namespace Prefix: | us-gaap_
Data Type: | us-types:surchargeItemType
Balance Type: | na
Period Type: | duration

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

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

X
- Details
Name: | us-gaap_RetirementPlanNameAxis=mdu_EdisonPensionPlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanNameAxis=mdu_LocalUnion212IbewPensionTrustFundMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanNameAxis=mdu_IBEWLocalNo.357PensionPlanAMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanNameAxis=mdu_IbewLocalNo82PensionPlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanNameAxis=mdu_IdahoPlumbersandPipefittersPensionPlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanNameAxis=mdu_NationalElectricalBenefitFundMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

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

X
- Details
Name: | us-gaap_RetirementPlanNameAxis=mdu_PensionAndRetirementPlanOfPlumbersAndPipefittersLocal525Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanNameAxis=mdu_PensionTrustFundforOperatingEngineersMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanNameAxis=mdu_SheetMetalWorkersPensionPlanofSouthernCAAZandNVMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanNameAxis=mdu_SouthernCaliforniaIBEWNECAPensionTrustFundMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanNameAxis=mdu_WesternConferenceOfTeamstersPensionPlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |