XML 111 R90.htm IDEA: XBRL DOCUMENT v2.4.1.9
Income tax expense (benefit) statutory rate versus actual rate (Details 5) (USD $)
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Computed tax at federal statutory rate      
Computed tax at federal statutory rate $ 143,895,000us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate $ 145,466,000us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate $ (15,914,000)us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate
Federal statutory rate (in hundredths) 35.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate 35.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate 35.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate
Increases (reductions) resulting from:      
State income taxes, net of federal income tax 10,483,000us-gaap_IncomeTaxReconciliationStateAndLocalIncomeTaxes 10,524,000us-gaap_IncomeTaxReconciliationStateAndLocalIncomeTaxes 2,469,000us-gaap_IncomeTaxReconciliationStateAndLocalIncomeTaxes
State income tax rate (in hundredths) 2.50%us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes 2.50%us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes (5.40%)us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes
Domestic production activities (5,460,000)us-gaap_IncomeTaxReconciliationDeductionsQualifiedProductionActivities (677,000)us-gaap_IncomeTaxReconciliationDeductionsQualifiedProductionActivities 0us-gaap_IncomeTaxReconciliationDeductionsQualifiedProductionActivities
Domestic production activities (in hundredths) (1.30%)us-gaap_EffectiveIncomeTaxRateReconciliationDeductionsQualifiedProductionActivities (0.20%)us-gaap_EffectiveIncomeTaxRateReconciliationDeductionsQualifiedProductionActivities 0.00%us-gaap_EffectiveIncomeTaxRateReconciliationDeductionsQualifiedProductionActivities
Nonqualified benefit plans (1,624,000)mdu_IncomeTaxReconciliationNonqualifiedBenefitPlans (5,173,000)mdu_IncomeTaxReconciliationNonqualifiedBenefitPlans (2,359,000)mdu_IncomeTaxReconciliationNonqualifiedBenefitPlans
Nonqualified benefit plans (in hundredths) (0.40%)mdu_EffectiveIncomeTaxRateReconciliationNonqualifiedBenefitPlans (1.20%)mdu_EffectiveIncomeTaxRateReconciliationNonqualifiedBenefitPlans 5.20%mdu_EffectiveIncomeTaxRateReconciliationNonqualifiedBenefitPlans
Depletion allowance (4,010,000)us-gaap_IncomeTaxReconciliationNondeductibleExpenseDepletion (3,764,000)us-gaap_IncomeTaxReconciliationNondeductibleExpenseDepletion (3,728,000)us-gaap_IncomeTaxReconciliationNondeductibleExpenseDepletion
Depletion allowance rate (in hundredths) (1.00%)us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseDepletion (0.90%)us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseDepletion 8.20%us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseDepletion
Federal renewable energy credit (3,655,000)us-gaap_IncomeTaxReconciliationTaxCreditsOther (3,404,000)us-gaap_IncomeTaxReconciliationTaxCreditsOther (3,401,000)us-gaap_IncomeTaxReconciliationTaxCreditsOther
Federal renewable energy credit rate (in hundreths) (0.90%)us-gaap_EffectiveIncomeTaxRateReconciliationTaxCreditsOther (0.80%)us-gaap_EffectiveIncomeTaxRateReconciliationTaxCreditsOther 7.50%us-gaap_EffectiveIncomeTaxRateReconciliationTaxCreditsOther
Deductible K-Plan dividends (2,062,000)us-gaap_IncomeTaxReconciliationDeductionsDividends (1,593,000)us-gaap_IncomeTaxReconciliationDeductionsDividends (2,829,000)us-gaap_IncomeTaxReconciliationDeductionsDividends
Deductible K-Plan dividends rate (in hundredths) (0.50%)us-gaap_EffectiveIncomeTaxRateReconciliationDeductionsDividends (0.40%)us-gaap_EffectiveIncomeTaxRateReconciliationDeductionsDividends 6.20%us-gaap_EffectiveIncomeTaxRateReconciliationDeductionsDividends
AFUDC equity (2,031,000)mdu_AfudcEquity (1,074,000)mdu_AfudcEquity (1,500,000)mdu_AfudcEquity
AFUDC equity rate (in hundredths) (0.50%)mdu_AfudcEquityRateInHundredths (0.30%)mdu_AfudcEquityRateInHundredths 3.30%mdu_AfudcEquityRateInHundredths
Resolution of tax matters and uncertain tax positions (7,367,000)us-gaap_IncomeTaxReconciliationTaxSettlements (859,000)us-gaap_IncomeTaxReconciliationTaxSettlements 2,559,000us-gaap_IncomeTaxReconciliationTaxSettlements
Resolution of tax matters and uncertain tax positions rate (in hundredths) (1.80%)us-gaap_EffectiveIncomeTaxRateReconciliationTaxSettlements (0.20%)us-gaap_EffectiveIncomeTaxRateReconciliationTaxSettlements (5.60%)us-gaap_EffectiveIncomeTaxRateReconciliationTaxSettlements
Deferred tax rate changes 9,000mdu_DeferredTaxRateChanges 741,000mdu_DeferredTaxRateChanges (3,083,000)mdu_DeferredTaxRateChanges
Deferred tax rate changes rate (in hundredths) 0.00%mdu_DeferredTaxRateChangesRateInHundredths 0.20%mdu_DeferredTaxRateChangesRateInHundredths 6.80%mdu_DeferredTaxRateChangesRateInHundredths
Other (8,209,000)us-gaap_IncomeTaxReconciliationOtherAdjustments (3,451,000)us-gaap_IncomeTaxReconciliationOtherAdjustments (3,360,000)us-gaap_IncomeTaxReconciliationOtherAdjustments
Other rate (in hundredths) (1.90%)us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments (0.80%)us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments 7.30%us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments
Total income tax expense (benefit) 119,969,000us-gaap_IncomeTaxExpenseBenefit 136,736,000us-gaap_IncomeTaxExpenseBenefit (31,146,000)us-gaap_IncomeTaxExpenseBenefit
Total income tax expense (benefit) rate (in hundredths) 29.20%us-gaap_EffectiveIncomeTaxRateContinuingOperations 32.90%us-gaap_EffectiveIncomeTaxRateContinuingOperations 68.50%us-gaap_EffectiveIncomeTaxRateContinuingOperations
Temporary differences [Abstract]      
Undistributed earnings from foreign operations 3,600,000mdu_UndistributedEarningsFromForeignOperations    
Deferred tax liabilities, undistributed foreign earnings $ 1,400,000us-gaap_DeferredTaxLiabilitiesUndistributedForeignEarnings