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Equity method investments (Details) | Aug. 31, 2013 | Aug. 31, 2012 | Nov. 30, 2011 | Nov. 30, 2010
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ECTE [Member] |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Percentage ownership interest in equity method investment sold |  |  |  | 59.96%mdu_PercentageOwnershipInterestInEquityMethodInvestmentSold / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = mdu_EcteMember
Portion of remaining interest sold | 25.00%mdu_RemainingInterest / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = mdu_EcteMember | 25.00%mdu_RemainingInterest / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = mdu_EcteMember | 25.00%mdu_RemainingInterest / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = mdu_EcteMember |
ENTE [Member] |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Percentage ownership interest in equity method investment sold |  |  |  | 100.00%mdu_PercentageOwnershipInterestInEquityMethodInvestmentSold / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = mdu_EnteMember
ERTE [Member] |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Percentage ownership interest in equity method investment sold |  |  |  | 100.00%mdu_PercentageOwnershipInterestInEquityMethodInvestmentSold / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = mdu_ErteMember

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- Definition Percentage ownership interest in equity method investment sold. + References No definition available. + Details
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Namespace Prefix: | mdu_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition Amount of remaining ownership interest sold. + References No definition available. + Details
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Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Details
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- Details
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- Details
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X
- Details
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