XML 146 R106.htm IDEA: XBRL DOCUMENT
v2.4.1.9

Multiemployer plans (Details 14) (USD $) | 12 Months Ended
--- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Multiemployer Plans [Line Items] |  |  |  |  |
Multiemployer plan red zone status funded percentage, maximum | 65.00%mdu_MultiemployerPlanRedZoneStatusFundedPercentageMaximum |  |  |  |
Multiemployer plan yellow zone status funded percentage, minimum | 65.00%mdu_MultiemployerPlanYellowZoneStatusFundedPercentageMinimum |  |  |  |
Mulitiemployer plan yellow status funded percentage, maximum | 80.00%mdu_MulitiemployerPlanYellowStatusFundedPercentageMaximum |  |  |  |
Multiemployer plan green zone status funded percentage, minimum | 80.00%mdu_MultiemployerPlanGreenZoneStatusFundedPercentageMinimum |  |  |  |
MEPP withdrawal liability, after tax | $ 8,400,000 mdu_EstimatedMultiemployerPlanWithdrawalObligationAfterTax |  |  |  |
Multiemployer plans, pension [Member] |  |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |  |
Multiemployer plan, withdrawal obligation | 14,000,000 us-gaap_MultiemployerPlansWithdrawalObligation / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember |  |  |  |
MEPP withdrawal liability, after tax | 8,400,000 mdu_EstimatedMultiemployerPlanWithdrawalObligationAfterTax / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember |  |  |  |
Multiemployer plan, period contributions | 42,817,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember |  | 39,260,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember |  | 34,779,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember
Edison Pension Plan [Member] | Multiemployer plans, pension [Member] |  |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |  |
Entity tax identification number | 936061681 |  |  |  |
Multiemployer plan number | 001 |  |  |  |
Multiemployer plans, certified zone status | Green |  | Green |  |
Multiemployer plans, certified zone status, date | Dec. 31, 2014 |  | Dec. 31, 2013 |  |
Multiemployer plans, funding improvement plan and rehabilitation plan | No |  |  |  |
Multiemployer plan, period contributions | 9,061,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_EdisonPensionPlanMember |  | 6,358,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_EdisonPensionPlanMember |  | 5,171,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_EdisonPensionPlanMember
Multiemployer plans, surcharge | No |  |  |  |
Multiemployer plans, collective-bargaining arrangement, expiration date | Dec. 31, 2014 | [1] |  |  |
IBEW Local 38 Pension Plan [Member] | Multiemployer plans, pension [Member] |  |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |  |
Entity tax identification number | 346574238 |  |  |  |
Multiemployer plan number | 001 |  |  |  |
Multiemployer plans, certified zone status | Yellow |  | Yellow |  |
Multiemployer plans, certified zone status, date | Apr. 30, 2014 |  | Apr. 30, 2013 |  |
Multiemployer plans, funding improvement plan and rehabilitation plan | Implemented |  |  |  |
Multiemployer plan, period contributions | 777,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_IbewLocal38PensionPlanMember |  | 1,041,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_IbewLocal38PensionPlanMember |  | 2,771,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_IbewLocal38PensionPlanMember
Multiemployer plans, surcharge | No |  |  |  |
Multiemployer plans, collective-bargaining arrangement, expiration date | Apr. 23, 2017 |  |  |  |
IBEW Local No. 82 Pension Plan [Member] | Multiemployer plans, pension [Member] |  |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |  |
Entity tax identification number | 316127268 |  |  |  |
Multiemployer plan number | 001 |  |  |  |
Multiemployer plans, certified zone status | Red |  | Red |  |
Multiemployer plans, certified zone status, date | Jun. 30, 2014 |  | Jun. 30, 2013 |  |
Multiemployer plans, funding improvement plan and rehabilitation plan | Implemented |  |  |  |
Multiemployer plan, period contributions | 1,392,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_IbewLocalNo82PensionPlanMember |  | 1,284,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_IbewLocalNo82PensionPlanMember |  | 1,093,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_IbewLocalNo82PensionPlanMember
Multiemployer plans, surcharge | No |  |  |  |
Multiemployer plans, collective-bargaining arrangement, expiration date | Nov. 29, 2015 |  |  |  |
IBEW Local No. 246 Pension Plan [Member] | Multiemployer plans, pension [Member] |  |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |  |
Entity tax identification number | 346582842 |  |  |  |
Multiemployer plan number | 001 |  |  |  |
Multiemployer plans, certified zone status | Yellow |  | Yellow |  |
Multiemployer plans, certified zone status, date | May 31, 2014 |  | May 31, 2013 |  |
Multiemployer plans, funding improvement plan and rehabilitation plan | Implemented |  |  |  |
Multiemployer plan, period contributions | 694,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_IBEWLocalNo.246PensionPlanMember |  | 1,848,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_IBEWLocalNo.246PensionPlanMember |  | 1,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_IBEWLocalNo.246PensionPlanMember
Multiemployer plans, surcharge | No |  |  |  |
Multiemployer plans, collective-bargaining arrangement, expiration date | Oct. 31, 2017 |  |  |  |
IBEW Local 648 Pension Plan [Member] | Multiemployer plans, pension [Member] |  |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |  |
Entity tax identification number | 316134845 |  |  |  |
Multiemployer plan number | 001 |  |  |  |
Multiemployer plans, certified zone status | Red |  | Red |  |
Multiemployer plans, certified zone status, date | Feb. 28, 2014 |  | Feb. 28, 2013 |  |
Multiemployer plans, funding improvement plan and rehabilitation plan | Implemented |  |  |  |
Multiemployer plan, period contributions | 1,110,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_IbewLocal648PensionPlanMember |  | 1,489,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_IbewLocal648PensionPlanMember |  | 564,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_IbewLocal648PensionPlanMember
Multiemployer plans, surcharge | No |  |  |  |
Multiemployer plans, collective-bargaining arrangement, expiration date | Aug. 31, 2015 |  |  |  |
Laborers Pension Trust Fund for Northern California [Member] | Multiemployer plans, pension [Member] |  |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |  |
Entity tax identification number | 946277608 |  |  |  |
Multiemployer plan number | 001 |  |  |  |
Multiemployer plans, certified zone status | Yellow |  | Yellow |  |
Multiemployer plans, certified zone status, date | May 31, 2014 |  | May 31, 2013 |  |
Multiemployer plans, funding improvement plan and rehabilitation plan | Implemented |  |  |  |
Multiemployer plan, period contributions | 663,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_LaborersPensionTrustFundForNorthernCaliforniaMember |  | 921,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_LaborersPensionTrustFundForNorthernCaliforniaMember |  | 567,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_LaborersPensionTrustFundForNorthernCaliforniaMember
Multiemployer plans, surcharge | No |  |  |  |
Multiemployer plans, collective-bargaining arrangement, expiration date | Jun. 30, 2016 |  |  |  |
National Electrical Benefit Fund [Member] | Multiemployer plans, pension [Member] |  |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |  |
Entity tax identification number | 530181657 |  |  |  |
Multiemployer plan number | 001 |  |  |  |
Multiemployer plans, certified zone status | Green |  | Green |  |
Multiemployer plans, funding improvement plan and rehabilitation plan | No |  |  |  |
Multiemployer plan, period contributions | 6,476,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_NationalElectricalBenefitFundMember |  | 5,883,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_NationalElectricalBenefitFundMember |  | 5,603,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_NationalElectricalBenefitFundMember
Multiemployer plans, surcharge | No |  |  |  |
Multiemployer plans, collective-bargaining arrangement, expiration date | Nov. 30, 2019 |  |  |  |
OE Pension Trust Fund [Member] | Multiemployer plans, pension [Member] |  |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |  |
Entity tax identification number | 946090764 |  |  |  |
Multiemployer plan number | 001 |  |  |  |
Multiemployer plans, certified zone status | Red |  | Yellow |  |
Multiemployer plans, certified zone status, date | Dec. 31, 2014 |  |  |  |
Multiemployer plans, funding improvement plan and rehabilitation plan | Implemented |  |  |  |
Multiemployer plan, period contributions | 1,445,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_OePensionTrustFundMember |  | 1,510,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_OePensionTrustFundMember |  | 1,156,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_OePensionTrustFundMember
Multiemployer plans, surcharge | No |  |  |  |
Multiemployer plans, collective-bargaining arrangement, expiration date, first | Jun. 15, 2015 |  |  |  |
Multiemployer plans, collective-bargaining arrangement, expiration date, last | Jun. 30, 2016 |  |  |  |
Operating Engineers Local 800 and WY Contractors Association Pension Plan for WY [Member] | Multiemployer plans, pension [Member] |  |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |  |
Entity tax identification number | 836011320 | [2] |  |  |
Multiemployer plan number | 001 |  |  |  |
Multiemployer plans, certified zone status | Red |  | Red |  |
Multiemployer plans, certified zone status, date | Dec. 31, 2014 |  | Dec. 31, 2013 |  |
Multiemployer plans, funding improvement plan and rehabilitation plan | Implemented |  |  |  |
Multiemployer plan, period contributions | 68,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_OperatingEngineersLocal800AndWyContractorsAssociationPensionPlanForWyMember |  | 76,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_OperatingEngineersLocal800AndWyContractorsAssociationPensionPlanForWyMember |  | 91,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_OperatingEngineersLocal800AndWyContractorsAssociationPensionPlanForWyMember
Multiemployer plans, surcharge | No |  |  |  |
Multiemployer plans, collective-bargaining arrangement, expiration date |  |  | Oct. 31, 2005 | [1] |
Operating Engineers Pension Trust [Member] | Multiemployer plans, pension [Member] |  |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |  |
Entity tax identification number | 956032478 |  |  |  |
Multiemployer plan number | 001 |  |  |  |
Multiemployer plans, certified zone status | Red |  | Red |  |
Multiemployer plans, certified zone status, date | Jun. 30, 2014 |  | Jun. 30, 2013 |  |
Multiemployer plans, funding improvement plan and rehabilitation plan | Implemented |  |  |  |
Multiemployer plan, period contributions | 612,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_OperatingEngineersPensionTrustMember |  | 493,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_OperatingEngineersPensionTrustMember |  | 761,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_OperatingEngineersPensionTrustMember
Multiemployer plans, surcharge | No |  |  |  |
Multiemployer plans, collective-bargaining arrangement, expiration date | Jul. 01, 2016 |  |  |  |
Sheet Metal Workers Pension Plan of Southern CA, AZ, and NV [Member] | Multiemployer plans, pension [Member] |  |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |  |
Entity tax identification number | 956052257 |  |  |  |
Multiemployer plan number | 001 |  |  |  |
Multiemployer plans, certified zone status | Red |  | Red |  |
Multiemployer plans, certified zone status, date | Dec. 31, 2014 |  | Dec. 31, 2013 |  |
Multiemployer plans, funding improvement plan and rehabilitation plan | Implemented |  |  |  |
Multiemployer plan, period contributions | 676,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_SheetMetalWorkersPensionPlanofSouthernCAAZandNVMember |  | 512,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_SheetMetalWorkersPensionPlanofSouthernCAAZandNVMember |  | 467,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_SheetMetalWorkersPensionPlanofSouthernCAAZandNVMember
Multiemployer plans, surcharge | No |  |  |  |
Multiemployer plans, collective-bargaining arrangement, expiration date | Jun. 30, 2015 |  |  |  |
Southwest Marine Pension Trust [Member] | Multiemployer plans, pension [Member] |  |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |  |
Entity tax identification number | 956123404 |  |  |  |
Multiemployer plan number | 001 |  |  |  |
Multiemployer plans, certified zone status | Red |  | Red |  |
Multiemployer plans, certified zone status, date | Dec. 31, 2014 |  | Dec. 31, 2013 |  |
Multiemployer plans, funding improvement plan and rehabilitation plan | Implemented |  |  |  |
Multiemployer plan, period contributions | 31,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_SouthwestMarinePensionTrustMember |  | 42,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_SouthwestMarinePensionTrustMember |  | 76,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = mdu_SouthwestMarinePensionTrustMember
Multiemployer plans, surcharge | No |  |  |  |
Multiemployer plans, collective-bargaining arrangement, expiration date, first | Jan. 31, 2014 | [1] |  |  |
Multiemployer plans, collective-bargaining arrangement, expiration date, last | Jan. 31, 2019 |  |  |  |
Other funds [Member] | Multiemployer plans, pension [Member] |  |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |  |
Multiemployer plan, period contributions | $ 19,812,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = us-gaap_MultiemployerPlanIndividuallyInsignificantMultiemployerPlansMember |  | $ 17,803,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = us-gaap_MultiemployerPlanIndividuallyInsignificantMultiemployerPlansMember |  | $ 16,458,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPensionMember / mdu_ScheduleOfMultiemployerPlanNameAxis = us-gaap_MultiemployerPlanIndividuallyInsignificantMultiemployerPlansMember
[1] | Plan includes collective bargaining agreements which have expired. The agreements contain provisions that automatically renew the existing contracts in lieu of a new negotiated collective bargaining agreement.
[2] | The Company withdrew from the plan as of October 26, 2014, as discussed below.

X
- Definition The Tax Identification Number (TIN), also known as an Employer Identification Number (EIN), is a unique 9-digit value assigned by the IRS. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation 12B -Number 240 -Section 12b -Subsection 1 + Details
Name: | dei_EntityTaxIdentificationNumber
Namespace Prefix: | dei_
Data Type: | dei:nineDigitItemType
Balance Type: | na
Period Type: | duration

X
- Definition Estimated multiemployer plan, withdrawal obligation, after tax. + References No definition available. + Details
Name: | mdu_EstimatedMultiemployerPlanWithdrawalObligationAfterTax
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Mulitiemployer plan yellow status funded percentage, maximum. + References No definition available. + Details
Name: | mdu_MulitiemployerPlanYellowStatusFundedPercentageMaximum
Namespace Prefix: | mdu_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Multiemployer plan green zone status funded percentage, minimum. + References No definition available. + Details
Name: | mdu_MultiemployerPlanGreenZoneStatusFundedPercentageMinimum
Namespace Prefix: | mdu_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Multiemployer plan red zone status funded percentage, maximum. + References No definition available. + Details
Name: | mdu_MultiemployerPlanRedZoneStatusFundedPercentageMaximum
Namespace Prefix: | mdu_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Multiemployer plan yellow zone status funded percentage, minimum. + References No definition available. + Details
Name: | mdu_MultiemployerPlanYellowZoneStatusFundedPercentageMinimum
Namespace Prefix: | mdu_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Three digit plan number for a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 5 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=35742057&loc=SL14450657-114947 + Details
Name: | us-gaap_MultiemployerPlanNumber
Namespace Prefix: | us-gaap_
Data Type: | us-types:threeDigitItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of contributions made to multiemployer plans by the employer. A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=35742057&loc=SL14450702-114947 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 9 -URI http://asc.fasb.org/extlink&oid=35742057&loc=SL14450691-114947 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 5 -Subparagraph (e)(1) -URI http://asc.fasb.org/extlink&oid=35742057&loc=SL14450657-114947 + Details
Name: | us-gaap_MultiemployerPlanPeriodContributions
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Indicate the multiemployer plan's certified zone status as currently required by the Pension Protection Act of 2006 or a subsequent amendment thereof. The zone status categories are red (critical status), orange (seriously endangered), yellow (endangered), and green (none of the above). The acceptable values are "red", "orange", "yellow", "green", "other", and "NA". A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 5 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=35742057&loc=SL14450657-114947 + Details
Name: | us-gaap_MultiemployerPlansCertifiedZoneStatus
Namespace Prefix: | us-gaap_
Data Type: | us-types:zoneStatusItemType
Balance Type: | na
Period Type: | duration

X
- Definition Date of the multiemployer plan's year end to which the certified zone status relates, in CCYY-MM-DD format. A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 5 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=35742057&loc=SL14450657-114947 + Details
Name: | us-gaap_MultiemployerPlansCertifiedZoneStatusDate
Namespace Prefix: | us-gaap_
Data Type: | xbrli:dateItemType
Balance Type: | na
Period Type: | duration

X
- Definition Expiration date of the collective bargaining arrangement requiring contributions to the multiemployer plan, in CCYY-MM-DD format. A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 5 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=35742057&loc=SL14450657-114947 + Details
Name: | us-gaap_MultiemployerPlansCollectiveBargainingArrangementExpirationDate
Namespace Prefix: | us-gaap_
Data Type: | xbrli:dateItemType
Balance Type: | na
Period Type: | duration

X
- Definition Expiration date of the collective bargaining arrangement requiring contributions to the multiemployer plan that will expire first in a group of associated collective bargaining arrangements, in CCYY-MM-DD format. A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 5 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=35742057&loc=SL14450657-114947 + Details
Name: | us-gaap_MultiemployerPlansCollectiveBargainingArrangementExpirationDateFirst
Namespace Prefix: | us-gaap_
Data Type: | xbrli:dateItemType
Balance Type: | na
Period Type: | duration

X
- Definition Expiration date of the collective bargaining arrangement requiring contributions to the multiemployer plan that will expire last in a group of associated collective bargaining arrangements, in CCYY-MM-DD format. A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 5 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=35742057&loc=SL14450657-114947 + Details
Name: | us-gaap_MultiemployerPlansCollectiveBargainingArrangementExpirationDateLast
Namespace Prefix: | us-gaap_
Data Type: | xbrli:dateItemType
Balance Type: | na
Period Type: | duration

X
- Definition Indicate whether a funding improvement plan or rehabilitation plan has been implemented or is pending for a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. The acceptable values are "no", "pending", "implemented", "other", and "NA". + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 5 -Subparagraph (f)(1) -URI http://asc.fasb.org/extlink&oid=35742057&loc=SL14450657-114947 + Details
Name: | us-gaap_MultiemployerPlansFundingImprovementPlanAndRehabilitationPlan
Namespace Prefix: | us-gaap_
Data Type: | us-types:fundingImprovementAndRehabilitationPlanItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_MultiemployerPlansLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Indicate whether the employer paid a surcharge to the pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. The acceptable values are "no", "yes", and "NA". + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 5 -Subparagraph (f)(2) -URI http://asc.fasb.org/extlink&oid=35742057&loc=SL14450657-114947 + Details
Name: | us-gaap_MultiemployerPlansSurcharge
Namespace Prefix: | us-gaap_
Data Type: | us-types:surchargeItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of the obligation recognized by withdrawing from a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. + References No definition available. + Details
Name: | us-gaap_MultiemployerPlansWithdrawalObligation
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Details
Name: | mdu_ScheduleOfMultiemployerPlanNameAxis=mdu_EdisonPensionPlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | mdu_ScheduleOfMultiemployerPlanNameAxis=mdu_IbewLocal38PensionPlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | mdu_ScheduleOfMultiemployerPlanNameAxis=mdu_IbewLocal648PensionPlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | mdu_ScheduleOfMultiemployerPlanNameAxis=mdu_IBEWLocalNo.246PensionPlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | mdu_ScheduleOfMultiemployerPlanNameAxis=mdu_IbewLocalNo82PensionPlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | mdu_ScheduleOfMultiemployerPlanNameAxis=mdu_LaborersPensionTrustFundForNorthernCaliforniaMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | mdu_ScheduleOfMultiemployerPlanNameAxis=mdu_NationalElectricalBenefitFundMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | mdu_ScheduleOfMultiemployerPlanNameAxis=mdu_OePensionTrustFundMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | mdu_ScheduleOfMultiemployerPlanNameAxis=mdu_OperatingEngineersLocal800AndWyContractorsAssociationPensionPlanForWyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | mdu_ScheduleOfMultiemployerPlanNameAxis=mdu_OperatingEngineersPensionTrustMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | mdu_ScheduleOfMultiemployerPlanNameAxis=mdu_SheetMetalWorkersPensionPlanofSouthernCAAZandNVMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | mdu_ScheduleOfMultiemployerPlanNameAxis=mdu_SouthwestMarinePensionTrustMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | mdu_ScheduleOfMultiemployerPlanNameAxis=us-gaap_MultiemployerPlanIndividuallyInsignificantMultiemployerPlansMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MultiemployerPlanTypeAxis=us-gaap_MultiemployerPlansPensionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |