XML 152 R74.htm IDEA: XBRL DOCUMENT
v2.4.1.9

Fair value measurements (Details 2) (USD $) | Dec. 31, 2014 | Dec. 31, 2013 | Jun. 30, 2013
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Concentration risks, percentage [Abstract] |  |  |  |  |
Percentage investment in common stock of mid-cap companies | 20.00%mdu_PercentageInvestmentInCommonStockOfMidCapCompanies |  | 29.00%mdu_PercentageInvestmentInCommonStockOfMidCapCompanies |  |
Percentage investment in common stock of small-cap companies | 18.00%mdu_PercentageInvestmentInCommonStockOfSmallCapCompanies |  | 28.00%mdu_PercentageInvestmentInCommonStockOfSmallCapCompanies |  |
Percentage investment in common stock of large-cap companies | 29.00%mdu_PercentageInvestmentInCommonStockOfLargeCapCompanies |  | 28.00%mdu_PercentageInvestmentInCommonStockOfLargeCapCompanies |  |
Percentage in fixed-income investments | 32.00%mdu_PercentageInFixedIncomeAndOtherInvestments |  | 15.00%mdu_PercentageInFixedIncomeAndOtherInvestments |  |
Percentage investment in cash and cash equivalents | 1.00%mdu_PercentageInvestmentinCashandCashEquivalents |  |  |  |
Assets, fair value disclosure, nonrecurring |  |  |  |  | $ 9,700,000 us-gaap_AssetsFairValueDisclosureNonrecurring
Fair value, measurements, recurring [Member] |  |  |  |  |
Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items] |  |  |  |  |
Assets: | 112,830,000 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 93,657,000 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  |
Liabilities: |  |  | 7,483,000 us-gaap_LiabilitiesFairValueDisclosure / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  |
Fair value, measurements, recurring [Member] | Commodity derivative instruments |  |  |  |  |
Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items] |  |  |  |  |
Liabilities: |  |  | 7,483,000 us-gaap_LiabilitiesFairValueDisclosure / us-gaap_FairValueByLiabilityClassAxis = us-gaap_CommodityMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  |
Fair value, measurements, recurring [Member] | Money market funds |  |  |  |  |
Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items] |  |  |  |  |
Assets: | 18,473,000 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_MoneyMarketFundsMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 19,227,000 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_MoneyMarketFundsMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  |
Fair value, measurements, recurring [Member] | Insurance contract [Member] |  |  |  |  |
Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items] |  |  |  |  |
Assets: | 65,831,000 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = mdu_InsuranceInvestmentContractMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [1] | 62,370,000 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = mdu_InsuranceInvestmentContractMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [2] |
Fair value, measurements, recurring [Member] | Mortgage-backed securities |  |  |  |  |
Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items] |  |  |  |  |
Assets: | 6,636,000 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 8,193,000 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  |
Fair value, measurements, recurring [Member] | U.S. Government securities [Member] |  |  |  |  |
Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items] |  |  |  |  |
Assets: | 3,555,000 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_USTreasurySecuritiesMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 1,917,000 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_USTreasurySecuritiesMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  |
Fair value, measurements, recurring [Member] | Commodity derivative instruments |  |  |  |  |
Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items] |  |  |  |  |
Assets: | 18,335,000 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_DerivativeFinancialInstrumentsAssetsMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 1,950,000 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_DerivativeFinancialInstrumentsAssetsMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  |
Fair value, measurements, recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) |  |  |  |  |
Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items] |  |  |  |  |
Assets: | 0 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  |
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Fair value, measurements, recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Commodity derivative instruments |  |  |  |  |
Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items] |  |  |  |  |
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Fair value, measurements, recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Money market funds |  |  |  |  |
Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items] |  |  |  |  |
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Fair value, measurements, recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Insurance contract [Member] |  |  |  |  |
Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items] |  |  |  |  |
Assets: | 0 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = mdu_InsuranceInvestmentContractMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [1] | 0 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = mdu_InsuranceInvestmentContractMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [2] |
Fair value, measurements, recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Mortgage-backed securities |  |  |  |  |
Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items] |  |  |  |  |
Assets: | 0 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  |
Fair value, measurements, recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Government securities [Member] |  |  |  |  |
Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items] |  |  |  |  |
Assets: | 0 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_USTreasurySecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_USTreasurySecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  |
Fair value, measurements, recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Commodity derivative instruments |  |  |  |  |
Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items] |  |  |  |  |
Assets: | 0 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_DerivativeFinancialInstrumentsAssetsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_DerivativeFinancialInstrumentsAssetsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  |
Fair value, measurements, recurring [Member] | Significant Other Observable Inputs (Level 2) |  |  |  |  |
Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items] |  |  |  |  |
Assets: | 112,830,000 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 93,657,000 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  |
Liabilities: |  |  | 7,483,000 us-gaap_LiabilitiesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  |
Fair value, measurements, recurring [Member] | Significant Other Observable Inputs (Level 2) | Commodity derivative instruments |  |  |  |  |
Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items] |  |  |  |  |
Liabilities: |  |  | 7,483,000 us-gaap_LiabilitiesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByLiabilityClassAxis = us-gaap_CommodityMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  |
Fair value, measurements, recurring [Member] | Significant Other Observable Inputs (Level 2) | Money market funds |  |  |  |  |
Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items] |  |  |  |  |
Assets: | 18,473,000 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_MoneyMarketFundsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 19,227,000 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_MoneyMarketFundsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  |
Fair value, measurements, recurring [Member] | Significant Other Observable Inputs (Level 2) | Insurance contract [Member] |  |  |  |  |
Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items] |  |  |  |  |
Assets: | 65,831,000 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = mdu_InsuranceInvestmentContractMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [1] | 62,370,000 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = mdu_InsuranceInvestmentContractMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [2] |
Fair value, measurements, recurring [Member] | Significant Other Observable Inputs (Level 2) | Mortgage-backed securities |  |  |  |  |
Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items] |  |  |  |  |
Assets: | 6,636,000 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 8,193,000 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  |
Fair value, measurements, recurring [Member] | Significant Other Observable Inputs (Level 2) | U.S. Government securities [Member] |  |  |  |  |
Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items] |  |  |  |  |
Assets: | 3,555,000 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_USTreasurySecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 1,917,000 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_USTreasurySecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  |
Fair value, measurements, recurring [Member] | Significant Other Observable Inputs (Level 2) | Commodity derivative instruments |  |  |  |  |
Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items] |  |  |  |  |
Assets: | 18,335,000 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_DerivativeFinancialInstrumentsAssetsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 1,950,000 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_DerivativeFinancialInstrumentsAssetsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  |
Fair value, measurements, recurring [Member] | Significant Unobservable Inputs (Level 3) |  |  |  |  |
Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items] |  |  |  |  |
Assets: | 0 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  |
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Fair value, measurements, recurring [Member] | Significant Unobservable Inputs (Level 3) | Commodity derivative instruments |  |  |  |  |
Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items] |  |  |  |  |
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Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items] |  |  |  |  |
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Fair value, measurements, recurring [Member] | Significant Unobservable Inputs (Level 3) | Insurance contract [Member] |  |  |  |  |
Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items] |  |  |  |  |
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Fair value, measurements, recurring [Member] | Significant Unobservable Inputs (Level 3) | Mortgage-backed securities |  |  |  |  |
Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items] |  |  |  |  |
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Fair value, measurements, recurring [Member] | Significant Unobservable Inputs (Level 3) | U.S. Government securities [Member] |  |  |  |  |
Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items] |  |  |  |  |
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Fair value, measurements, recurring [Member] | Significant Unobservable Inputs (Level 3) | Commodity derivative instruments |  |  |  |  |
Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items] |  |  |  |  |
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[1] | The insurance contract invests approximately 20 percent in common stock of mid-cap companies, 18 percent in common stock of small-cap companies, 29 percent in common stock of large-cap companies, 32 percent in fixed-income investments and 1 percent in cash equivalents.
[2] | The insurance contract invests approximately 29 percent in common stock of mid-cap companies, 28 percent in common stock of small-cap companies, 28 percent in common stock of large-cap companies and 15 percent in fixed-income investments.

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- Definition Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
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- Definition Fair value of financial and nonfinancial obligations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
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