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Short-term borrowings (Details 2) (Short-term debt [Member], Cascade Natural Gas Corporation [Member], Revolving credit agreement [Member])	Dec. 31, 2013
Short-term debt [Member] | Cascade Natural Gas Corporation [Member] | Revolving credit agreement [Member]
Short-term debt [Line Items]
Weighted average interest rate	3.30%
Ratio of total debt to total capitalization as specified in debt convenants.	65.00%

X

- Definition

Ratio of total debt to total capitalization as specified in debt convenants.

+ References

No definition available.

+ Details

Name:	mdu_RatioOfTotalDebtToTotalCapitalizationAsSpecifiedInDebtConvenants
Namespace Prefix:	mdu_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Weighted average interest rate of debt outstanding.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtWeightedAverageInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Details

Name:	us-gaap_ShortTermDebtLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration