XML 140 R107.htm IDEA: XBRL DOCUMENT
v2.4.1.9

Multiemployer other postretirement and defined contribution plans (Details 15) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Multiemployer Plans, Defined Contribution [Member] |  |  |
Multiemployer Plans [Line Items] |  |  |
Multiemployer plan, period contributions | $ 22,000 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_DefinedContributionPlanNameAxis = mdu_MultiemployerPlansDefinedContributionMember | $ 20,600 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_DefinedContributionPlanNameAxis = mdu_MultiemployerPlansDefinedContributionMember | $ 18,700 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_DefinedContributionPlanNameAxis = mdu_MultiemployerPlansDefinedContributionMember
Multiemployer Plans, Postretirement Benefit [Member] |  |  |
Multiemployer Plans [Line Items] |  |  |
Multiemployer plan, period contributions | $ 34,600 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPostretirementBenefitMember | $ 37,100 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPostretirementBenefitMember | $ 31,400 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_MultiemployerPlanTypeAxis = us-gaap_MultiemployerPlansPostretirementBenefitMember

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

X
- Details
Name: | us-gaap_DefinedContributionPlanNameAxis=mdu_MultiemployerPlansDefinedContributionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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