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Derivative instruments (Details 9)	12 Months Ended
	Dec. 31, 2013
Accounting Policies [Abstract]
Maximum length of time allowed to hedge forecasted sales	42 months
Maximum length of time allowed to hedge interest rate	24 months
Maximum length of time allowed to hedge foreign currency	12-month period
Maximum length of time allowed to hedge forecasted purchases	three years
Maximum period for settlement of all interest rate derivative transactions	90 days
Maximum period for settlement of foreign currency derivative transactions	12-month period

X

- Definition

Maximum length of time over which the entity is hedging its exposure to the variability in future cash flows for forecasted sales transactions, excluding those forecasted transactions related to the payment of variable interest on existing financial instruments.

+ References

No definition available.

+ Details

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Namespace Prefix:	mdu_
Data Type:	us-types:durationStringItemType
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Period Type:	duration

X

- Definition

Maximum length of time over which the entity is hedging its exposure to the variability in future cash flows for forecasted purchase transactions, excluding those forecasted transactions related to the payment of variable interest on existing financial instruments.

+ References

No definition available.

+ Details

Name:	mdu_MaximumLengthOfTimeAllowedToHedgeInCashFlowHedgePurchase
Namespace Prefix:	mdu_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Maximum length of time over which the entity is hedging its exposure to foreign currency.

+ References

No definition available.

+ Details

Name:	mdu_MaximumLengthOfTimeAllowedToHedgeInForeignCurrencyCashFlowHedge
Namespace Prefix:	mdu_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Maximum length of time over which the entity is hedging its exposure to the variability in future cash flows for forecasted transactions, excluding those forecasted transactions related to the payment of variable interest on existing financial instruments.

+ References

No definition available.

+ Details

Name:	mdu_MaximumLengthOfTimeAllowedToHedgeInInterestRateCashFlowHedge
Namespace Prefix:	mdu_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Maximum length of time for the settlement of all interest rate derivative transactions.

+ References

No definition available.

+ Details

Name:	mdu_MaximumPeriodForSettlementOfAllInterestRateDerivativeTransactions
Namespace Prefix:	mdu_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Maximum length of time for the settlement of foreign currency derivative transactions.

+ References

No definition available.

+ Details

Name:	mdu_MaximumPeriodForSettlementOfForeignCurrencyDerivativeTransactions
Namespace Prefix:	mdu_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

X

- Details

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