XML 29 R44.htm IDEA: XBRL DOCUMENT
v2.4.0.6

Income taxes (Details) (USD $) | 3 Months Ended
--- | ---
Mar. 31, 2012 | Mar. 31, 2011
Income Tax Disclosure [Abstract] |  |
Income tax expense for unrecognized tax positions | $ 2,200,000 |
Reduction in deferred income tax expense due to deferred income tax rate reduction | 2,500,000 |
Income tax benefit from continuing operations |  | 4,200,000
Unrecognized tax benefits, decreases resulting from settlements with taxing authorities |  | 2,800,000
Interest related to reversal of unrecognized tax benefits previously established for 2004 through 2006 tax years |  | $ 600,000

X
- Definition Income tax benefit from continuing operations resulting from resolution of certain tax matters. + References No definition available. + Details
Name: | mdu_IncomeTaxBenefitFromContinuingOperations
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | duration

X
- Definition Income tax expense for unrecognized tax positions. + References No definition available. + Details
Name: | mdu_IncomeTaxExpenseForUnrecognizedTaxPositions
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | duration

X
- Definition Interest associated with unrecognized tax benefits resulting from settlements with taxing authorities. + References No definition available. + Details
Name: | mdu_InterestRelatedToReversalOfUnrecognizedTaxBenefitsPreviouslyEstablishedFor2004Through2006TaxYears
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Reduction in deferred income tax expense due to deferred income tax rate reduction. + References No definition available. + Details
Name: | mdu_ReductionInDeferredIncomeTaxExpenseDueToDeferredIncomeTaxRateReduction
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | duration

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

X
- Definition The gross amount of decreases in unrecognized tax benefits resulting from settlements with taxing authorities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Interpretation (FIN) -Number 48 -Paragraph 21 -Subparagraph a(3) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319 + Details
Name: | us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration