XML 84 R70.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Derivative instruments gains and losses on derivative instruments (Details 9) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2015 USD ($)
Commodity derivatives [Member] | Not designated as hedging instrument [Member] | Exploration and production [Member] |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |
Amount of gain (loss) recognized in discontinued operations, before tax | $ (18.3)

X
- Definition Amount of gain (loss) recognized in earnings in the period from the increase (decrease) in fair value of price risk derivatives not designated as hedging instruments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959 + Details
Name: | us-gaap_GainLossOnPriceRiskDerivativeInstrumentsNotDesignatedAsHedgingInstruments
Namespace Prefix: | us-gaap_
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_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=mdu_CommodityDerivativesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_HedgingDesignationAxis=us-gaap_NondesignatedMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DisposalGroupClassificationAxis=mdu_ExplorationAndProductionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |