XML 82 R70.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Montana Public Service Commission (MTPSC) (Details 2) - MTPSC - Natural gas rate proceeding - USD ($) | Apr. 24, 2018 | Feb. 23, 2018 | Jan. 12, 2018 | Sep. 25, 2017
--- | --- | --- | --- | ---
Public Utilities, General Disclosures [Line Items] |  |  |  |
Public utilities, requested rate increase (decrease), amount |  | $ 2,800,000 |  | $ 2,800,000
Public utilities, requested rate increase (decrease), percentage |  |  |  | 4.10%
Public utilities, interim rate increase (decrease), amount |  |  |  | $ 1,600,000
Public utilities, interim rate increase (decrease), percentage |  |  |  | 2.30%
Tax Cuts and Jobs Act |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |
Public utilities, requested rate increase (decrease), amended, amount |  | $ 1,600,000 |  |
Public utilities interm rate increase (decrese) revised |  |  | $ 764,000 |
Subsequent Event | Tax Cuts and Jobs Act |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |
Public utilities, requested rate increase (decrease), amended, amount | $ 975,000 |  |  |
Public utilities, requested rate increase (decrease), amended, percentage | 1.40% |  |  |

X
- Definition Public utilities interim rate increase (decrease), revised + References No definition available. + Details
Name: | mdu_PublicUtilitiesIntermRateIncreaseDecreseRevised
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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_PublicUtilitiesGeneralDisclosuresLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of public utility's interim rate increase (decrease) allowed while waiting final decision of regulatory agency. + References No definition available. + Details
Name: | us-gaap_PublicUtilitiesInterimRateIncreaseDecreaseAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Percentage of public utility's interim rate increase (decrease) allowed while waiting final decision of regulatory agency. + References No definition available. + Details
Name: | us-gaap_PublicUtilitiesInterimRateIncreaseDecreasePercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of public utility's amended requested rate increase (decrease) with regulatory agency. + References No definition available. + Details
Name: | us-gaap_PublicUtilitiesRequestedRateIncreaseDecreaseAmendedAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Percentage of public utility's amended requested rate increase (decrease) with regulatory agency. + References No definition available. + Details
Name: | us-gaap_PublicUtilitiesRequestedRateIncreaseDecreaseAmendedPercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of public utility's requested rate increase (decrease) with regulatory agency. + References No definition available. + Details
Name: | us-gaap_PublicUtilitiesRequestedRateIncreaseDecreaseAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Percentage of public utility's requested rate increase (decrease) with regulatory agency. + References No definition available. + Details
Name: | us-gaap_PublicUtilitiesRequestedRateIncreaseDecreasePercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_RegulatoryAgencyAxis=mdu_MtpscMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PublicUtilitiesRegulatoryProceedingAxis=mdu_NaturalgasrateproceedingMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_IncomeTaxAuthorityAxis=mdu_TaxCutsandJobsActMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |