XML 129 R105.htm IDEA: XBRL DOCUMENT
v3.3.1.900

Defined contribution plans (Details 12) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Nonqualified Defined Contribution Plan [Member] |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Defined contribution plan, cost recognized | $ 207,000 | $ 104,000 | $ 25,000
Defined Contribution Plan [Member] |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Defined contribution plan, cost recognized | $ 36,800,000 | $ 34,400,000 | $ 33,200,000

X
- Definition The amount of the cost recognized during the period for defined contribution plans. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942 + Details
Name: | us-gaap_DefinedContributionPlanCostRecognized
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_DefinedContributionPlanDisclosureLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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

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