XML 161 R134.htm IDEA: XBRL DOCUMENT
v3.22.0.1

Enviromental matters (Details 2) | 12 Months Ended
--- | ---
Dec. 31, 2021 USD ($)
Portland Harbor Site |
Site Contingency [Line Items] |
Environmental matters investigative costs | $ 115,000,000
Environmental matters, estimated costs | 1,000,000,000
Missoula, MT manufactured gas plant site |
Site Contingency [Line Items] |
Total estimated costs for site remediation | 560,000
Environmental Matters Estimated Investigative Costs | 823,000
Environmental matters accrual for site remediation | 419,000
Incurred Costs For Site Remedial Investigation | 505,000
Bremerton, WA manufactured gas plant site |
Site Contingency [Line Items] |
Environmental matters accrual for site remediation | 17,500,000
Total estimated costs for site remedial investigation and feasibility study | 7,600,000
Incurred costs for site remedial investigation and feasibility study | 5,300,000
Environmental matters accrual of investigative costs | 2,300,000
Bellingham, WA manufactured gas plant site |
Site Contingency [Line Items] |
Site contingency, loss exposure not accrued, preferred alternative estimate | 9,300,000
Minimum | Bremerton, WA manufactured gas plant site |
Site Contingency [Line Items] |
Site contingency, loss exposure not accrued, best estimate | 13,600,000
Minimum | Bellingham, WA manufactured gas plant site |
Site Contingency [Line Items] |
Site contingency, loss exposure not accrued, best estimate | 8,000,000
Maximum | Bremerton, WA manufactured gas plant site |
Site Contingency [Line Items] |
Site contingency, loss exposure not accrued, best estimate | 71,000,000
Maximum | Bellingham, WA manufactured gas plant site |
Site Contingency [Line Items] |
Site contingency, loss exposure not accrued, best estimate | $ 20,400,000

X
- Definition Environmental matters accrual for remedial investigation and feasibility study costs. + References No definition available. + Details
Name: | mdu_EnvironmentalMattersAccrualForRemedialInvestigationandFeasibilityStudyCosts
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Environmental matters accrual for site remediation + References No definition available. + Details
Name: | mdu_EnvironmentalMattersAccrualForSiteRemediation
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Environmental matters, estimated costs. + References No definition available. + Details
Name: | mdu_EnvironmentalMattersEstimatedCosts
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Environmental Matters Estimated Investigative Costs + References No definition available. + Details
Name: | mdu_EnvironmentalMattersEstimatedInvestigativeCosts
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Estimated investigative costs. + References No definition available. + Details
Name: | mdu_EnvironmentalMattersInvestigativeCosts
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Incurred Costs For Site Remedial Investigation + References No definition available. + Details
Name: | mdu_IncurredCostsForSiteRemedialInvestigation
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Incurred costs for site remedial investigation and feasibility study + References No definition available. + Details
Name: | mdu_IncurredCostsForSiteRemedialInvestigationAndFeasibilityStudy
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Preferred alternative cost estimate of the loss exposure for reasonably possible environmental contingencies at an individual site + References No definition available. + Details
Name: | mdu_SiteContingencyLossExposureNotAccruedPreferredAlternativeEstimate
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Total estimated costs for site remedial investigation and feasibility study + References No definition available. + Details
Name: | mdu_TotalEstimatedCostsForSiteRemedialInvestigationAndFeasibilityStudy
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Total estimated costs for site remediation + References No definition available. + Details
Name: | mdu_TotalEstimatedCostsForSiteRemediation
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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_SiteContingencyLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Best estimate of the loss exposure for reasonably possible environmental contingencies at an individual site for which no accrual has been recorded. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 30 -Section 50 -Paragraph 10 -Subparagraph (c),(d)(2) -URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13237-110859 Reference 2: http://www.xbrl.org/2003/role/recommendedDisclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 30 -Section 50 -Paragraph 10 -Subparagraph (d)(2) -URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13237-110859 + Details
Name: | us-gaap_SiteContingencyLossExposureNotAccruedBestEstimate
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_EnvironmentalRemediationSiteAxis=mdu_PortlandHarborSiteMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EnvironmentalRemediationSiteAxis=mdu_MissoulaMTmanufacturedgasplantsiteMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EnvironmentalRemediationSiteAxis=mdu_BremertonWAManufacturedGasPlantSiteMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EnvironmentalRemediationSiteAxis=mdu_BellinghamWAManufacturedGasPlantSiteMember
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: |