The amount of requested interim increase in annual gas rates.

No definition available.

Name:	mdu_AmountOfRequestedInterimIncreaseInAnnualGasRates
Namespace Prefix:	mdu_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

The percentage of interim gas rate increase requested.

No definition available.

Name:	mdu_RequestedPercentageOfInterimGasRateIncrease
Namespace Prefix:	mdu_
Data Type:	num:percentItemType
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Amount of public utility's approved rate increase (decrease) by regulatory agency.

No definition available.

Name:	us-gaap_PublicUtilitiesApprovedRateIncreaseDecreaseAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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Amount of public utility's interim rate increase (decrease) allowed while waiting final decision of regulatory agency.

No definition available.

Name:	us-gaap_PublicUtilitiesInterimRateIncreaseDecreaseAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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Percentage of public utility's interim rate increase (decrease) allowed while waiting final decision of regulatory agency.

No definition available.

Name:	us-gaap_PublicUtilitiesInterimRateIncreaseDecreasePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
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Amount of public utility's requested rate increase (decrease) with regulatory agency.

No definition available.

Name:	us-gaap_PublicUtilitiesRequestedRateIncreaseDecreaseAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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Period Type:	duration

Percentage of public utility's requested rate increase (decrease) with regulatory agency.

No definition available.

Name:	us-gaap_PublicUtilitiesRequestedRateIncreaseDecreasePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

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Regulatory matters and revenues subject to refund (Details) (USD $)	0 Months Ended
	Aug. 11, 2014	Oct. 03, 2014	Feb. 03, 2015	Jan. 07, 2015	Feb. 06, 2015
MTPSC [Member]
Regulatory matters and revenues subject to refund [Line Items]
Total gas rate increase requested	$ 3,000,000
Percent above current rates requested	3.60%
WYPSC [Member]
Regulatory matters and revenues subject to refund [Line Items]
Total gas rate increase requested		788,000
Percent above current rates requested		4.10%
Subsequent Event [Member] \| MTPSC [Member]
Regulatory matters and revenues subject to refund [Line Items]
Interim rate increase (decrease), amount			2,000,000
Interim rate increase (decrease), percent			2.30%
Subsequent Event [Member] \| NDPSC-Generation [Member]
Regulatory matters and revenues subject to refund [Line Items]
Approved rate adjustment increase (decrease), amount				5,300,000
Subsequent Event [Member] \| NDPSC [Member]
Regulatory matters and revenues subject to refund [Line Items]
Total gas rate increase requested					4,300,000
Percent above current rates requested					3.40%
Amount of requested interim increase in annual gas rates					$ 4,300,000
Requested percentage of interim gas rate increase					3.40%