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