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Regulatory matters and revenues subject to refund (Details) (MTPSC [Member], USD $) In Millions, unless otherwise specified | Sep. 26, 2012
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MTPSC [Member] |
Regulatory matters and revenues subject to refund [Line Items] |
Total gas rate increase requested | $ 3.5
Percent above current rates requested | 5.90%
Amount of requested interim increase in annual gas rates | $ 1.7
Requested percentage of interim gas rate increase | 2.90%
Number of days to be effective within | 30 days

X
- Definition The amount of requested interim increase in annual gas rates. + References No definition available. + Details
Name: | mdu_AmountOfRequestedInterimIncreaseInAnnualGasRates
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The number of days for interim request to be effective within. + References No definition available. + Details
Name: | mdu_NumberOfDaysToBeEffectiveWithin
Namespace Prefix: | mdu_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | instant

X
- Definition The percentage of the annual increase in rates over current rates requested. + References No definition available. + Details
Name: | mdu_PercentAboveCurrentRatesRequested
Namespace Prefix: | mdu_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | mdu_RegulatoryMattersAndRevenuesSubjectToRefundLineItems
Namespace Prefix: | mdu_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The percentage of interim gas rate increase requested. + References No definition available. + Details
Name: | mdu_RequestedPercentageOfInterimGasRateIncrease
Namespace Prefix: | mdu_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The total amount of the annual increase in gas rates requested. + References No definition available. + Details
Name: | mdu_TotalGasRateIncreaseRequested
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant