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Regulatory matters and revenues subject to refund (Details) (USD $) | 3 Months Ended
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Mar. 31, 2012
Regulatory matters and revenues subject to refund [Abstract] |
Estimated project cost of the natural gas turbine and associated facilities | $ 85,600,000
Annual reduction in rates | $ 250,000

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- Definition Annual reduction in rates. + References No definition available. + Details
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Period Type: | duration

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- Definition Estimated project cost of the natural gas turbine and associated facilities. + References No definition available. + Details
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Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Details
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Namespace Prefix: | mdu_
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