XML 130 R92.htm IDEA: XBRL DOCUMENT
v2.4.1.9

Business segment data (Details) (USD $) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2014 | Sep. 30, 2014 | Jun. 30, 2014 | Mar. 31, 2014 | Dec. 31, 2013 | Sep. 30, 2013 | Jun. 30, 2013 | Mar. 31, 2013 | Dec. 31, 2012 | Sep. 30, 2012 | Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Business segment data [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
External operating revenues | $ 1,163,204,000 us-gaap_Revenues |  | $ 1,370,455,000 us-gaap_Revenues | $ 1,094,046,000 us-gaap_Revenues | $ 1,042,853,000 us-gaap_Revenues | $ 1,184,423,000 us-gaap_Revenues |  | $ 1,285,782,000 us-gaap_Revenues | $ 1,060,595,000 us-gaap_Revenues | $ 931,604,000 us-gaap_Revenues |  |  |  | $ 4,670,558,000 us-gaap_Revenues |  | $ 4,462,404,000 us-gaap_Revenues |  | $ 4,075,431,000 us-gaap_Revenues |
Intersegment operating revenues |  |  |  |  |  |  |  |  |  |  |  |  |  | 0 mdu_Intersegmentoperatingrevenues |  | 0 mdu_Intersegmentoperatingrevenues |  | 0 mdu_Intersegmentoperatingrevenues |
Depreciation, depletion and amortization |  |  |  |  |  |  |  |  |  |  |  |  |  | 401,368,000 us-gaap_DepreciationDepletionAndAmortization |  | 386,856,000 us-gaap_DepreciationDepletionAndAmortization |  | 359,205,000 us-gaap_DepreciationDepletionAndAmortization |
Interest expense |  |  |  |  |  |  |  |  |  |  |  |  |  | 87,016,000 us-gaap_InterestExpense |  | 83,917,000 us-gaap_InterestExpense |  | 76,699,000 us-gaap_InterestExpense |
Income taxes |  |  |  |  |  |  |  |  |  |  |  |  |  | 119,969,000 us-gaap_IncomeTaxExpenseBenefit |  | 136,736,000 us-gaap_IncomeTaxExpenseBenefit |  | (31,146,000)us-gaap_IncomeTaxExpenseBenefit |
Earnings (loss) on common stock before income (loss) from discontinued operations |  |  |  |  |  |  |  |  |  |  |  |  |  | 294,371,000 mdu_Earningslossoncommonstockbeforeincomelossfromdiscontinuedoperations |  | 278,560,000 mdu_Earningslossoncommonstockbeforeincomelossfromdiscontinuedoperations |  | (15,006,000)mdu_Earningslossoncommonstockbeforeincomelossfromdiscontinuedoperations |
Income (loss) from discontinued operations, net of tax | 2,672,000 us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax |  | 3,000 us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax | 547,000 us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax | (45,000)us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax | (58,000)us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax |  | (118,000)us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax | (59,000)us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax | (77,000)us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax |  |  |  | 3,177,000 us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax | [1] | (312,000)us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax | [1] | 13,567,000 us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax | [1]
Total earnings (loss) on common stock |  |  |  |  |  |  |  |  |  |  |  |  |  | 297,548,000 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic |  | 278,248,000 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic |  | (1,439,000)us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic |
Net proceeds from sale or disposition of property and other |  |  |  |  |  |  |  |  |  |  |  |  |  | (306,994,000)us-gaap_PropertyPlantAndEquipmentDisposals |  | (112,131,000)us-gaap_PropertyPlantAndEquipmentDisposals |  | (57,460,000)us-gaap_PropertyPlantAndEquipmentDisposals |
Total net capital expenditures |  |  |  |  |  |  |  |  |  |  |  |  |  | 843,690,000 us-gaap_PropertyPlantAndEquipmentGrossPeriodIncreaseDecrease |  | 728,070,000 us-gaap_PropertyPlantAndEquipmentGrossPeriodIncreaseDecrease |  | 933,777,000 us-gaap_PropertyPlantAndEquipmentGrossPeriodIncreaseDecrease |
Total assets | 7,809,978,000 us-gaap_Assets |  |  |  |  | 7,061,332,000 us-gaap_Assets |  |  |  |  | 6,682,491,000 us-gaap_Assets |  |  | 7,809,978,000 us-gaap_Assets |  | 7,061,332,000 us-gaap_Assets |  | 6,682,491,000 us-gaap_Assets |
Property, plant and equipment | 9,693,171,000 us-gaap_PropertyPlantAndEquipmentGross |  |  |  |  | 8,803,866,000 us-gaap_PropertyPlantAndEquipmentGross |  |  |  |  |  |  |  | 9,693,171,000 us-gaap_PropertyPlantAndEquipmentGross |  | 8,803,866,000 us-gaap_PropertyPlantAndEquipmentGross |  |  |
Less accumulated depreciation, depletion and amortization | 4,166,407,000 us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment |  |  |  |  | 3,872,487,000 us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment |  |  |  |  | 3,608,912,000 us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment |  |  | 4,166,407,000 us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment |  | 3,872,487,000 us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment |  | 3,608,912,000 us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment |
Net property, plant and equipment | 5,526,764,000 us-gaap_PropertyPlantAndEquipmentNet |  |  |  |  | 4,931,379,000 us-gaap_PropertyPlantAndEquipmentNet |  |  |  |  | 4,498,839,000 us-gaap_PropertyPlantAndEquipmentNet |  |  | 5,526,764,000 us-gaap_PropertyPlantAndEquipmentNet |  | 4,931,379,000 us-gaap_PropertyPlantAndEquipmentNet |  | 4,498,839,000 us-gaap_PropertyPlantAndEquipmentNet |
Additional information [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Write-downs of oil and natural gas properties |  |  |  |  |  |  |  |  |  |  | 231,700,000 us-gaap_ImpairmentOfOilAndGasProperties |  | 160,100,000 us-gaap_ImpairmentOfOilAndGasProperties | 0 us-gaap_ImpairmentOfOilAndGasProperties |  | 0 us-gaap_ImpairmentOfOilAndGasProperties |  | 391,800,000 us-gaap_ImpairmentOfOilAndGasProperties |
Noncash write-down of natural gas and oil properties, after tax |  |  |  |  |  |  |  |  |  |  | 145,900,000 mdu_ImpairmentOfOilAndGasPropertiesAfterTax |  | 100,900,000 mdu_ImpairmentOfOilAndGasPropertiesAfterTax |  |  |  |  | 246,800,000 mdu_ImpairmentOfOilAndGasPropertiesAfterTax |
Asset impairment charges |  |  |  |  |  |  |  |  | 9,000,000 us-gaap_AssetImpairmentCharges |  |  |  |  |  |  | 9,000,000 us-gaap_AssetImpairmentCharges |  | 1,700,000 us-gaap_AssetImpairmentCharges |
Reversal of an arbitration charge after tax |  |  |  |  |  | 1,500,000 mdu_ReversalOfArbitrationChargeAfterTax |  |  |  |  |  |  |  |  |  | 1,500,000 mdu_ReversalOfArbitrationChargeAfterTax |  | 15,000,000 mdu_ReversalOfArbitrationChargeAfterTax |
Net noncash inclusion of acct pay and NCI exclusion of capital expenditures |  |  |  |  |  |  |  |  |  |  |  |  |  | (61,200,000)mdu_NetNoncashInclusionofAcctPayandNCIExclusionsofCapitalExpenditures |  | (56,800,000)mdu_NetNoncashInclusionofAcctPayandNCIExclusionsofCapitalExpenditures |  | 33,700,000 mdu_NetNoncashInclusionofAcctPayandNCIExclusionsofCapitalExpenditures |
Electric: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business segment data [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
External operating revenues |  |  |  |  |  |  |  |  |  |  |  |  |  | 277,874,000 us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = mdu_ElectricMember |  | 257,260,000 us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = mdu_ElectricMember |  | 236,895,000 us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = mdu_ElectricMember |
Intersegment operating revenues |  |  |  |  |  |  |  |  |  |  |  |  |  | 0 mdu_Intersegmentoperatingrevenues / us-gaap_StatementBusinessSegmentsAxis = mdu_ElectricMember |  | 0 mdu_Intersegmentoperatingrevenues / us-gaap_StatementBusinessSegmentsAxis = mdu_ElectricMember |  | 0 mdu_Intersegmentoperatingrevenues / us-gaap_StatementBusinessSegmentsAxis = mdu_ElectricMember |
Depreciation, depletion and amortization |  |  |  |  |  |  |  |  |  |  |  |  |  | 35,008,000 us-gaap_DepreciationDepletionAndAmortization / us-gaap_StatementBusinessSegmentsAxis = mdu_ElectricMember |  | 32,789,000 us-gaap_DepreciationDepletionAndAmortization / us-gaap_StatementBusinessSegmentsAxis = mdu_ElectricMember |  | 32,509,000 us-gaap_DepreciationDepletionAndAmortization / us-gaap_StatementBusinessSegmentsAxis = mdu_ElectricMember |
Interest expense |  |  |  |  |  |  |  |  |  |  |  |  |  | 15,595,000 us-gaap_InterestExpense / us-gaap_StatementBusinessSegmentsAxis = mdu_ElectricMember |  | 12,590,000 us-gaap_InterestExpense / us-gaap_StatementBusinessSegmentsAxis = mdu_ElectricMember |  | 12,421,000 us-gaap_InterestExpense / us-gaap_StatementBusinessSegmentsAxis = mdu_ElectricMember |
Income taxes |  |  |  |  |  |  |  |  |  |  |  |  |  | 12,442,000 us-gaap_IncomeTaxExpenseBenefit / us-gaap_StatementBusinessSegmentsAxis = mdu_ElectricMember |  | 9,683,000 us-gaap_IncomeTaxExpenseBenefit / us-gaap_StatementBusinessSegmentsAxis = mdu_ElectricMember |  | 8,975,000 us-gaap_IncomeTaxExpenseBenefit / us-gaap_StatementBusinessSegmentsAxis = mdu_ElectricMember |
Earnings (loss) on common stock before income (loss) from discontinued operations |  |  |  |  |  |  |  |  |  |  |  |  |  | 36,731,000 mdu_Earningslossoncommonstockbeforeincomelossfromdiscontinuedoperations / us-gaap_StatementBusinessSegmentsAxis = mdu_ElectricMember |  | 34,837,000 mdu_Earningslossoncommonstockbeforeincomelossfromdiscontinuedoperations / us-gaap_StatementBusinessSegmentsAxis = mdu_ElectricMember |  | 30,634,000 mdu_Earningslossoncommonstockbeforeincomelossfromdiscontinuedoperations / us-gaap_StatementBusinessSegmentsAxis = mdu_ElectricMember |
Capital expenditures |  |  |  |  |  |  |  |  |  |  |  |  |  | 185,121,000 us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_StatementBusinessSegmentsAxis = mdu_ElectricMember |  | 168,557,000 us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_StatementBusinessSegmentsAxis = mdu_ElectricMember |  | 112,035,000 us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_StatementBusinessSegmentsAxis = mdu_ElectricMember |
Total assets | 1,030,611,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_ElectricMember | [2] |  |  |  | 884,283,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_ElectricMember | [2] |  |  |  | 760,324,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_ElectricMember | [2] |  | 1,030,611,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_ElectricMember | [2] | 884,283,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_ElectricMember | [2] | 760,324,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_ElectricMember | [2]
Property, plant and equipment | 1,457,101,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_ElectricMember | [2] |  |  |  | 1,315,822,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_ElectricMember | [2] |  |  |  | 1,150,584,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_ElectricMember | [2] |  | 1,457,101,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_ElectricMember | [2] | 1,315,822,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_ElectricMember | [2] | 1,150,584,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_ElectricMember | [2]
Natural gas distribution: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business segment data [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
External operating revenues |  |  |  |  |  |  |  |  |  |  |  |  |  | 921,986,000 us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = mdu_NaturalGasDistributionMember |  | 851,945,000 us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = mdu_NaturalGasDistributionMember |  | 754,848,000 us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = mdu_NaturalGasDistributionMember |
Intersegment operating revenues |  |  |  |  |  |  |  |  |  |  |  |  |  | 0 mdu_Intersegmentoperatingrevenues / us-gaap_StatementBusinessSegmentsAxis = mdu_NaturalGasDistributionMember |  | 0 mdu_Intersegmentoperatingrevenues / us-gaap_StatementBusinessSegmentsAxis = mdu_NaturalGasDistributionMember |  | 0 mdu_Intersegmentoperatingrevenues / us-gaap_StatementBusinessSegmentsAxis = mdu_NaturalGasDistributionMember |
Depreciation, depletion and amortization |  |  |  |  |  |  |  |  |  |  |  |  |  | 54,700,000 us-gaap_DepreciationDepletionAndAmortization / us-gaap_StatementBusinessSegmentsAxis = mdu_NaturalGasDistributionMember |  | 50,031,000 us-gaap_DepreciationDepletionAndAmortization / us-gaap_StatementBusinessSegmentsAxis = mdu_NaturalGasDistributionMember |  | 45,731,000 us-gaap_DepreciationDepletionAndAmortization / us-gaap_StatementBusinessSegmentsAxis = mdu_NaturalGasDistributionMember |
Interest expense |  |  |  |  |  |  |  |  |  |  |  |  |  | 27,217,000 us-gaap_InterestExpense / us-gaap_StatementBusinessSegmentsAxis = mdu_NaturalGasDistributionMember |  | 25,123,000 us-gaap_InterestExpense / us-gaap_StatementBusinessSegmentsAxis = mdu_NaturalGasDistributionMember |  | 28,726,000 us-gaap_InterestExpense / us-gaap_StatementBusinessSegmentsAxis = mdu_NaturalGasDistributionMember |
Income taxes |  |  |  |  |  |  |  |  |  |  |  |  |  | 11,350,000 us-gaap_IncomeTaxExpenseBenefit / us-gaap_StatementBusinessSegmentsAxis = mdu_NaturalGasDistributionMember |  | 16,633,000 us-gaap_IncomeTaxExpenseBenefit / us-gaap_StatementBusinessSegmentsAxis = mdu_NaturalGasDistributionMember |  | 12,005,000 us-gaap_IncomeTaxExpenseBenefit / us-gaap_StatementBusinessSegmentsAxis = mdu_NaturalGasDistributionMember |
Earnings (loss) on common stock before income (loss) from discontinued operations |  |  |  |  |  |  |  |  |  |  |  |  |  | 30,484,000 mdu_Earningslossoncommonstockbeforeincomelossfromdiscontinuedoperations / us-gaap_StatementBusinessSegmentsAxis = mdu_NaturalGasDistributionMember |  | 37,656,000 mdu_Earningslossoncommonstockbeforeincomelossfromdiscontinuedoperations / us-gaap_StatementBusinessSegmentsAxis = mdu_NaturalGasDistributionMember |  | 29,409,000 mdu_Earningslossoncommonstockbeforeincomelossfromdiscontinuedoperations / us-gaap_StatementBusinessSegmentsAxis = mdu_NaturalGasDistributionMember |
Capital expenditures |  |  |  |  |  |  |  |  |  |  |  |  |  | 120,613,000 us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_StatementBusinessSegmentsAxis = mdu_NaturalGasDistributionMember |  | 101,279,000 us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_StatementBusinessSegmentsAxis = mdu_NaturalGasDistributionMember |  | 130,178,000 us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_StatementBusinessSegmentsAxis = mdu_NaturalGasDistributionMember |
Total assets | 1,931,908,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_NaturalGasDistributionMember | [2] |  |  |  | 1,786,068,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_NaturalGasDistributionMember | [2] |  |  |  | 1,703,459,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_NaturalGasDistributionMember | [2] |  | 1,931,908,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_NaturalGasDistributionMember | [2] | 1,786,068,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_NaturalGasDistributionMember | [2] | 1,703,459,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_NaturalGasDistributionMember | [2]
Property, plant and equipment | 1,904,759,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_NaturalGasDistributionMember | [2] |  |  |  | 1,776,901,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_NaturalGasDistributionMember | [2] |  |  |  | 1,689,950,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_NaturalGasDistributionMember | [2] |  | 1,904,759,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_NaturalGasDistributionMember | [2] | 1,776,901,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_NaturalGasDistributionMember | [2] | 1,689,950,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_NaturalGasDistributionMember | [2]
Pipeline and energy services: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business segment data [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
External operating revenues |  |  |  |  |  |  |  |  |  |  |  |  |  | 166,496,000 us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = mdu_PipelineAndEnergyServicesMember |  | 155,369,000 us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = mdu_PipelineAndEnergyServicesMember |  | 139,883,000 us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = mdu_PipelineAndEnergyServicesMember |
Intersegment operating revenues |  |  |  |  |  |  |  |  |  |  |  |  |  | 49,372,000 mdu_Intersegmentoperatingrevenues / us-gaap_StatementBusinessSegmentsAxis = mdu_PipelineAndEnergyServicesMember |  | 46,699,000 mdu_Intersegmentoperatingrevenues / us-gaap_StatementBusinessSegmentsAxis = mdu_PipelineAndEnergyServicesMember |  | 53,274,000 mdu_Intersegmentoperatingrevenues / us-gaap_StatementBusinessSegmentsAxis = mdu_PipelineAndEnergyServicesMember |
Depreciation, depletion and amortization |  |  |  |  |  |  |  |  |  |  |  |  |  | 30,645,000 us-gaap_DepreciationDepletionAndAmortization / us-gaap_StatementBusinessSegmentsAxis = mdu_PipelineAndEnergyServicesMember |  | 29,119,000 us-gaap_DepreciationDepletionAndAmortization / us-gaap_StatementBusinessSegmentsAxis = mdu_PipelineAndEnergyServicesMember |  | 27,684,000 us-gaap_DepreciationDepletionAndAmortization / us-gaap_StatementBusinessSegmentsAxis = mdu_PipelineAndEnergyServicesMember |
Interest expense |  |  |  |  |  |  |  |  |  |  |  |  |  | 10,048,000 us-gaap_InterestExpense / us-gaap_StatementBusinessSegmentsAxis = mdu_PipelineAndEnergyServicesMember |  | 10,330,000 us-gaap_InterestExpense / us-gaap_StatementBusinessSegmentsAxis = mdu_PipelineAndEnergyServicesMember |  | 7,742,000 us-gaap_InterestExpense / us-gaap_StatementBusinessSegmentsAxis = mdu_PipelineAndEnergyServicesMember |
Income taxes |  |  |  |  |  |  |  |  |  |  |  |  |  | 9,699,000 us-gaap_IncomeTaxExpenseBenefit / us-gaap_StatementBusinessSegmentsAxis = mdu_PipelineAndEnergyServicesMember |  | 3,390,000 us-gaap_IncomeTaxExpenseBenefit / us-gaap_StatementBusinessSegmentsAxis = mdu_PipelineAndEnergyServicesMember |  | 15,291,000 us-gaap_IncomeTaxExpenseBenefit / us-gaap_StatementBusinessSegmentsAxis = mdu_PipelineAndEnergyServicesMember |
Earnings (loss) on common stock before income (loss) from discontinued operations |  |  |  |  |  |  |  |  |  |  |  |  |  | 22,628,000 mdu_Earningslossoncommonstockbeforeincomelossfromdiscontinuedoperations / us-gaap_StatementBusinessSegmentsAxis = mdu_PipelineAndEnergyServicesMember |  | 7,629,000 mdu_Earningslossoncommonstockbeforeincomelossfromdiscontinuedoperations / us-gaap_StatementBusinessSegmentsAxis = mdu_PipelineAndEnergyServicesMember |  | 26,588,000 mdu_Earningslossoncommonstockbeforeincomelossfromdiscontinuedoperations / us-gaap_StatementBusinessSegmentsAxis = mdu_PipelineAndEnergyServicesMember |
Capital expenditures |  |  |  |  |  |  |  |  |  |  |  |  |  | 177,409,000 us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_StatementBusinessSegmentsAxis = mdu_PipelineAndEnergyServicesMember |  | 127,092,000 us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_StatementBusinessSegmentsAxis = mdu_PipelineAndEnergyServicesMember |  | 133,787,000 us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_StatementBusinessSegmentsAxis = mdu_PipelineAndEnergyServicesMember |
Total assets | 1,081,902,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_PipelineAndEnergyServicesMember |  |  |  |  | 798,701,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_PipelineAndEnergyServicesMember |  |  |  |  | 622,470,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_PipelineAndEnergyServicesMember |  |  | 1,081,902,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_PipelineAndEnergyServicesMember |  | 798,701,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_PipelineAndEnergyServicesMember |  | 622,470,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_PipelineAndEnergyServicesMember |
Property, plant and equipment | 1,220,233,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_PipelineAndEnergyServicesMember |  |  |  |  | 962,172,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_PipelineAndEnergyServicesMember |  |  |  |  | 816,533,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_PipelineAndEnergyServicesMember |  |  | 1,220,233,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_PipelineAndEnergyServicesMember |  | 962,172,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_PipelineAndEnergyServicesMember |  | 816,533,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_PipelineAndEnergyServicesMember |
Exploration and production: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business segment data [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
External operating revenues |  |  |  |  |  |  |  |  |  |  |  |  |  | 500,526,000 us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = mdu_ExplorationAndProductionMember |  | 490,924,000 us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = mdu_ExplorationAndProductionMember |  | 412,651,000 us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = mdu_ExplorationAndProductionMember |
Intersegment operating revenues |  |  |  |  |  |  |  |  |  |  |  |  |  | 47,045,000 mdu_Intersegmentoperatingrevenues / us-gaap_StatementBusinessSegmentsAxis = mdu_ExplorationAndProductionMember |  | 45,099,000 mdu_Intersegmentoperatingrevenues / us-gaap_StatementBusinessSegmentsAxis = mdu_ExplorationAndProductionMember |  | 35,966,000 mdu_Intersegmentoperatingrevenues / us-gaap_StatementBusinessSegmentsAxis = mdu_ExplorationAndProductionMember |
Depreciation, depletion and amortization |  |  |  |  |  |  |  |  |  |  |  |  |  | 198,199,000 us-gaap_DepreciationDepletionAndAmortization / us-gaap_StatementBusinessSegmentsAxis = mdu_ExplorationAndProductionMember |  | 186,458,000 us-gaap_DepreciationDepletionAndAmortization / us-gaap_StatementBusinessSegmentsAxis = mdu_ExplorationAndProductionMember |  | 160,681,000 us-gaap_DepreciationDepletionAndAmortization / us-gaap_StatementBusinessSegmentsAxis = mdu_ExplorationAndProductionMember |
Interest expense |  |  |  |  |  |  |  |  |  |  |  |  |  | 13,834,000 us-gaap_InterestExpense / us-gaap_StatementBusinessSegmentsAxis = mdu_ExplorationAndProductionMember |  | 14,315,000 us-gaap_InterestExpense / us-gaap_StatementBusinessSegmentsAxis = mdu_ExplorationAndProductionMember |  | 9,018,000 us-gaap_InterestExpense / us-gaap_StatementBusinessSegmentsAxis = mdu_ExplorationAndProductionMember |
Income taxes |  |  |  |  |  |  |  |  |  |  |  |  |  | 47,739,000 us-gaap_IncomeTaxExpenseBenefit / us-gaap_StatementBusinessSegmentsAxis = mdu_ExplorationAndProductionMember |  | 53,197,000 us-gaap_IncomeTaxExpenseBenefit / us-gaap_StatementBusinessSegmentsAxis = mdu_ExplorationAndProductionMember |  | (108,264,000)us-gaap_IncomeTaxExpenseBenefit / us-gaap_StatementBusinessSegmentsAxis = mdu_ExplorationAndProductionMember |
Earnings (loss) on common stock before income (loss) from discontinued operations |  |  |  |  |  |  |  |  |  |  |  |  |  | 96,733,000 mdu_Earningslossoncommonstockbeforeincomelossfromdiscontinuedoperations / us-gaap_StatementBusinessSegmentsAxis = mdu_ExplorationAndProductionMember |  | 94,450,000 mdu_Earningslossoncommonstockbeforeincomelossfromdiscontinuedoperations / us-gaap_StatementBusinessSegmentsAxis = mdu_ExplorationAndProductionMember |  | (177,283,000)mdu_Earningslossoncommonstockbeforeincomelossfromdiscontinuedoperations / us-gaap_StatementBusinessSegmentsAxis = mdu_ExplorationAndProductionMember |
Capital expenditures |  |  |  |  |  |  |  |  |  |  |  |  |  | 600,572,000 us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_StatementBusinessSegmentsAxis = mdu_ExplorationAndProductionMember |  | 391,315,000 us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_StatementBusinessSegmentsAxis = mdu_ExplorationAndProductionMember |  | 554,528,000 us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_StatementBusinessSegmentsAxis = mdu_ExplorationAndProductionMember |
Total assets | 1,738,064,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_ExplorationAndProductionMember |  |  |  |  | 1,616,131,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_ExplorationAndProductionMember |  |  |  |  | 1,539,017,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_ExplorationAndProductionMember |  |  | 1,738,064,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_ExplorationAndProductionMember |  | 1,616,131,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_ExplorationAndProductionMember |  | 1,539,017,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_ExplorationAndProductionMember |
Property, plant and equipment | 3,402,879,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_ExplorationAndProductionMember |  |  |  |  | 3,060,848,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_ExplorationAndProductionMember |  |  |  |  | 2,764,560,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_ExplorationAndProductionMember |  |  | 3,402,879,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_ExplorationAndProductionMember |  | 3,060,848,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_ExplorationAndProductionMember |  | 2,764,560,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_ExplorationAndProductionMember |
Construction materials and contracting: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business segment data [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
External operating revenues |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,740,089,000 us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionMaterialsAndContractingMember |  | 1,675,444,000 us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionMaterialsAndContractingMember |  | 1,597,257,000 us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionMaterialsAndContractingMember |
Intersegment operating revenues |  |  |  |  |  |  |  |  |  |  |  |  |  | 25,241,000 mdu_Intersegmentoperatingrevenues / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionMaterialsAndContractingMember |  | 36,693,000 mdu_Intersegmentoperatingrevenues / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionMaterialsAndContractingMember |  | 20,168,000 mdu_Intersegmentoperatingrevenues / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionMaterialsAndContractingMember |
Depreciation, depletion and amortization |  |  |  |  |  |  |  |  |  |  |  |  |  | 68,557,000 us-gaap_DepreciationDepletionAndAmortization / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionMaterialsAndContractingMember |  | 74,470,000 us-gaap_DepreciationDepletionAndAmortization / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionMaterialsAndContractingMember |  | 79,527,000 us-gaap_DepreciationDepletionAndAmortization / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionMaterialsAndContractingMember |
Interest expense |  |  |  |  |  |  |  |  |  |  |  |  |  | 16,368,000 us-gaap_InterestExpense / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionMaterialsAndContractingMember |  | 17,394,000 us-gaap_InterestExpense / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionMaterialsAndContractingMember |  | 15,211,000 us-gaap_InterestExpense / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionMaterialsAndContractingMember |
Income taxes |  |  |  |  |  |  |  |  |  |  |  |  |  | 18,586,000 us-gaap_IncomeTaxExpenseBenefit / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionMaterialsAndContractingMember |  | 24,765,000 us-gaap_IncomeTaxExpenseBenefit / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionMaterialsAndContractingMember |  | 14,099,000 us-gaap_IncomeTaxExpenseBenefit / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionMaterialsAndContractingMember |
Earnings (loss) on common stock before income (loss) from discontinued operations |  |  |  |  |  |  |  |  |  |  |  |  |  | 51,510,000 mdu_Earningslossoncommonstockbeforeincomelossfromdiscontinuedoperations / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionMaterialsAndContractingMember |  | 50,946,000 mdu_Earningslossoncommonstockbeforeincomelossfromdiscontinuedoperations / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionMaterialsAndContractingMember |  | 32,420,000 mdu_Earningslossoncommonstockbeforeincomelossfromdiscontinuedoperations / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionMaterialsAndContractingMember |
Capital expenditures |  |  |  |  |  |  |  |  |  |  |  |  |  | 37,896,000 us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionMaterialsAndContractingMember |  | 34,607,000 us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionMaterialsAndContractingMember |  | 45,083,000 us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionMaterialsAndContractingMember |
Total assets | 1,272,231,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionMaterialsAndContractingMember |  |  |  |  | 1,305,808,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionMaterialsAndContractingMember |  |  |  |  | 1,371,252,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionMaterialsAndContractingMember |  |  | 1,272,231,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionMaterialsAndContractingMember |  | 1,305,808,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionMaterialsAndContractingMember |  | 1,371,252,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionMaterialsAndContractingMember |
Property, plant and equipment | 1,529,942,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionMaterialsAndContractingMember |  |  |  |  | 1,510,355,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionMaterialsAndContractingMember |  |  |  |  | 1,504,981,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionMaterialsAndContractingMember |  |  | 1,529,942,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionMaterialsAndContractingMember |  | 1,510,355,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionMaterialsAndContractingMember |  | 1,504,981,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionMaterialsAndContractingMember |
Construction services: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business segment data [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
External operating revenues |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,062,055,000 us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionServicesMember |  | 1,029,909,000 us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionServicesMember |  | 932,013,000 us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionServicesMember |
Intersegment operating revenues |  |  |  |  |  |  |  |  |  |  |  |  |  | 57,474,000 mdu_Intersegmentoperatingrevenues / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionServicesMember |  | 9,930,000 mdu_Intersegmentoperatingrevenues / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionServicesMember |  | 6,545,000 mdu_Intersegmentoperatingrevenues / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionServicesMember |
Depreciation, depletion and amortization |  |  |  |  |  |  |  |  |  |  |  |  |  | 12,874,000 us-gaap_DepreciationDepletionAndAmortization / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionServicesMember |  | 11,939,000 us-gaap_DepreciationDepletionAndAmortization / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionServicesMember |  | 11,063,000 us-gaap_DepreciationDepletionAndAmortization / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionServicesMember |
Interest expense |  |  |  |  |  |  |  |  |  |  |  |  |  | 4,176,000 us-gaap_InterestExpense / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionServicesMember |  | 4,306,000 us-gaap_InterestExpense / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionServicesMember |  | 4,435,000 us-gaap_InterestExpense / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionServicesMember |
Income taxes |  |  |  |  |  |  |  |  |  |  |  |  |  | 24,753,000 us-gaap_IncomeTaxExpenseBenefit / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionServicesMember |  | 29,504,000 us-gaap_IncomeTaxExpenseBenefit / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionServicesMember |  | 24,128,000 us-gaap_IncomeTaxExpenseBenefit / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionServicesMember |
Earnings (loss) on common stock before income (loss) from discontinued operations |  |  |  |  |  |  |  |  |  |  |  |  |  | 54,432,000 mdu_Earningslossoncommonstockbeforeincomelossfromdiscontinuedoperations / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionServicesMember |  | 52,213,000 mdu_Earningslossoncommonstockbeforeincomelossfromdiscontinuedoperations / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionServicesMember |  | 38,429,000 mdu_Earningslossoncommonstockbeforeincomelossfromdiscontinuedoperations / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionServicesMember |
Capital expenditures |  |  |  |  |  |  |  |  |  |  |  |  |  | 26,942,000 us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionServicesMember |  | 15,102,000 us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionServicesMember |  | 14,835,000 us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionServicesMember |
Total assets | 454,602,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionServicesMember |  |  |  |  | 450,614,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionServicesMember |  |  |  |  | 429,547,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionServicesMember |  |  | 454,602,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionServicesMember |  | 450,614,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionServicesMember |  | 429,547,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionServicesMember |
Property, plant and equipment | 144,395,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionServicesMember |  |  |  |  | 134,948,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionServicesMember |  |  |  |  | 130,624,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionServicesMember |  |  | 144,395,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionServicesMember |  | 134,948,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionServicesMember |  | 130,624,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = mdu_ConstructionServicesMember |
Other |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business segment data [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
External operating revenues |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,532,000 us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember |  | 1,553,000 us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember |  | 1,884,000 us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember |
Intersegment operating revenues |  |  |  |  |  |  |  |  |  |  |  |  |  | 7,832,000 mdu_Intersegmentoperatingrevenues / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember |  | 8,067,000 mdu_Intersegmentoperatingrevenues / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember |  | 8,486,000 mdu_Intersegmentoperatingrevenues / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember |
Depreciation, depletion and amortization |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,196,000 us-gaap_DepreciationDepletionAndAmortization / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember |  | 2,050,000 us-gaap_DepreciationDepletionAndAmortization / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember |  | 2,010,000 us-gaap_DepreciationDepletionAndAmortization / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember |
Interest expense |  |  |  |  |  |  |  |  |  |  |  |  |  | 15,000 us-gaap_InterestExpense / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember |  | 15,000 us-gaap_InterestExpense / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember |  | 13,000 us-gaap_InterestExpense / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember |
Income taxes |  |  |  |  |  |  |  |  |  |  |  |  |  | (1,119,000)us-gaap_IncomeTaxExpenseBenefit / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember |  | 2,433,000 us-gaap_IncomeTaxExpenseBenefit / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember |  | 2,620,000 us-gaap_IncomeTaxExpenseBenefit / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember |
Earnings (loss) on common stock before income (loss) from discontinued operations |  |  |  |  |  |  |  |  |  |  |  |  |  | 7,461,000 mdu_Earningslossoncommonstockbeforeincomelossfromdiscontinuedoperations / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember |  | 5,136,000 mdu_Earningslossoncommonstockbeforeincomelossfromdiscontinuedoperations / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember |  | 4,797,000 mdu_Earningslossoncommonstockbeforeincomelossfromdiscontinuedoperations / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember |
Capital expenditures |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,131,000 us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember |  | 2,249,000 us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember |  | 791,000 us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember |
Total assets | 300,660,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember | [3] |  |  |  | 219,727,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember | [3] |  |  |  | 256,422,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember | [3] |  | 300,660,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember | [3] | 219,727,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember | [3] | 256,422,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember | [3]
Property, plant and equipment | 50,937,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember |  |  |  |  | 49,997,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember |  |  |  |  | 50,519,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember |  |  | 50,937,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember |  | 49,997,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember |  | 50,519,000 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember |
Eliminations |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business segment data [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Intersegment operating revenues |  |  |  |  |  |  |  |  |  |  |  |  |  | (186,964,000)mdu_Intersegmentoperatingrevenues / us-gaap_StatementBusinessSegmentsAxis = us-gaap_IntersegmentEliminationMember |  | (146,488,000)mdu_Intersegmentoperatingrevenues / us-gaap_StatementBusinessSegmentsAxis = us-gaap_IntersegmentEliminationMember |  | (124,439,000)mdu_Intersegmentoperatingrevenues / us-gaap_StatementBusinessSegmentsAxis = us-gaap_IntersegmentEliminationMember |
Depreciation, depletion and amortization |  |  |  |  |  |  |  |  |  |  |  |  |  | (811,000)us-gaap_DepreciationDepletionAndAmortization / us-gaap_StatementBusinessSegmentsAxis = us-gaap_IntersegmentEliminationMember |  | 0 us-gaap_DepreciationDepletionAndAmortization / us-gaap_StatementBusinessSegmentsAxis = us-gaap_IntersegmentEliminationMember |  | 0 us-gaap_DepreciationDepletionAndAmortization / us-gaap_StatementBusinessSegmentsAxis = us-gaap_IntersegmentEliminationMember |
Interest expense |  |  |  |  |  |  |  |  |  |  |  |  |  | (237,000)us-gaap_InterestExpense / us-gaap_StatementBusinessSegmentsAxis = us-gaap_IntersegmentEliminationMember |  | (156,000)us-gaap_InterestExpense / us-gaap_StatementBusinessSegmentsAxis = us-gaap_IntersegmentEliminationMember |  | (867,000)us-gaap_InterestExpense / us-gaap_StatementBusinessSegmentsAxis = us-gaap_IntersegmentEliminationMember |
Income taxes |  |  |  |  |  |  |  |  |  |  |  |  |  | (3,481,000)us-gaap_IncomeTaxExpenseBenefit / us-gaap_StatementBusinessSegmentsAxis = us-gaap_IntersegmentEliminationMember |  | (2,869,000)us-gaap_IncomeTaxExpenseBenefit / us-gaap_StatementBusinessSegmentsAxis = us-gaap_IntersegmentEliminationMember |  | 0 us-gaap_IncomeTaxExpenseBenefit / us-gaap_StatementBusinessSegmentsAxis = us-gaap_IntersegmentEliminationMember |
Earnings (loss) on common stock before income (loss) from discontinued operations |  |  |  |  |  |  |  |  |  |  |  |  |  | (5,608,000)mdu_Earningslossoncommonstockbeforeincomelossfromdiscontinuedoperations / us-gaap_StatementBusinessSegmentsAxis = us-gaap_IntersegmentEliminationMember |  | (4,307,000)mdu_Earningslossoncommonstockbeforeincomelossfromdiscontinuedoperations / us-gaap_StatementBusinessSegmentsAxis = us-gaap_IntersegmentEliminationMember |  | 0 mdu_Earningslossoncommonstockbeforeincomelossfromdiscontinuedoperations / us-gaap_StatementBusinessSegmentsAxis = us-gaap_IntersegmentEliminationMember |
Property, plant and equipment | (17,075,000)us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = us-gaap_IntersegmentEliminationMember |  |  |  |  | (7,177,000)us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = us-gaap_IntersegmentEliminationMember |  |  |  |  | 0 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = us-gaap_IntersegmentEliminationMember |  |  | (17,075,000)us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = us-gaap_IntersegmentEliminationMember |  | (7,177,000)us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = us-gaap_IntersegmentEliminationMember |  | 0 us-gaap_PropertyPlantAndEquipmentGross / us-gaap_StatementBusinessSegmentsAxis = us-gaap_IntersegmentEliminationMember |
Regulated: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business segment data [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
External operating revenues |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,366,356,000 us-gaap_Revenues / us-gaap_PublicUtilityRegulatedOrUnregulatedStatusAxis = us-gaap_RegulatedOperationMember |  | 1,264,574,000 us-gaap_Revenues / us-gaap_PublicUtilityRegulatedOrUnregulatedStatusAxis = us-gaap_RegulatedOperationMember |  | 1,131,626,000 us-gaap_Revenues / us-gaap_PublicUtilityRegulatedOrUnregulatedStatusAxis = us-gaap_RegulatedOperationMember |
Nonregulated: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business segment data [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
External operating revenues |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 3,304,202,000 us-gaap_Revenues / us-gaap_PublicUtilityRegulatedOrUnregulatedStatusAxis = us-gaap_UnregulatedOperationMember |  | $ 3,197,830,000 us-gaap_Revenues / us-gaap_PublicUtilityRegulatedOrUnregulatedStatusAxis = us-gaap_UnregulatedOperationMember |  | $ 2,943,805,000 us-gaap_Revenues / us-gaap_PublicUtilityRegulatedOrUnregulatedStatusAxis = us-gaap_UnregulatedOperationMember |
[1] | Reflected in the Other category.
[2] | Includes allocations of common utility property.
[3] | Includes assets not directly assignable to a business (i.e. cash and cash equivalents, certain accounts receivable, certain investments and other miscellaneous current and deferred assets).

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