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

Approximate annual increase in revenues based on adjusted base period volumes.

No definition available.

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

Increased investments covered by change application.

No definition available.

The percentage of interim gas rate increase requested.

No definition available.

Name:	mdu_RequestedPercentageOfInterimGasRateIncrease
Namespace Prefix:	mdu_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

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
Balance Type:	credit
Period Type:	duration

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

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
Balance Type:	credit
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

Regulatory matters and revenues subject to refund (Details) (USD $)	0 Months Ended
	Jul. 10, 2014 NDPSC [Member]	Feb. 27, 2014 NDPSC [Member]	Aug. 11, 2014 MTPSC [Member]	Oct. 31, 2013 FERC [Member]	Oct. 03, 2014 Subsequent event [Member] WYPSC [Member]
Regulatory matters and revenues subject to refund [Line Items]
Annual amount recovered	$ 8,600,000
Rate increase requested		7,400,000	3,000,000		788,000
Percent above current rates requested		4.60%	3.60%		4.10%
Interim rate increase (decrease), amount			2,200,000
Interim rate increase, percent			2.60%
Increased expenditures covered by change application				312,000,000
Approximate annual increase in revenues				$ 11,500,000