XML 68 R100.htm IDEA: XBRL DOCUMENT
v2.4.1.9

Fair value (Details 8) | Dec. 31, 2014
--- | ---
Pension Benefits |
Defined Benefit Plan Disclosure [Line Items] |
Number of investment managers of plan assets | 15 mdu_NumberOfInvestmentManagersOfPlanAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember
Other Postretirement Benefits |
Defined Benefit Plan Disclosure [Line Items] |
Number of investment managers of plan assets | 1 mdu_NumberOfInvestmentManagersOfPlanAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember

X
- Definition Number of Investment Managers of Plan Assets + References No definition available. + Details
Name: | mdu_NumberOfInvestmentManagersOfPlanAssets
Namespace Prefix: | mdu_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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

X
- Details
Name: | us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis=us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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