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Litigation (Details) (USD $)	0 Months Ended
	Aug. 06, 2012	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Oct. 31, 2010	Aug. 31, 2011	Mar. 12, 2015
Loss Contingencies [Line Items]
Potential liabilities related to litigation and environmental matters		$ 25,800,000us-gaap_LossContingencyAccrualAtCarryingValue	$ 27,600,000us-gaap_LossContingencyAccrualAtCarryingValue	$ 31,400,000us-gaap_LossContingencyAccrualAtCarryingValue
Natural gas gathering operations [Member]
Loss Contingencies [Line Items]
Arbitration award					26,600,000mdu_ArbitrationAward / us-gaap_LitigationCaseAxis = mdu_NaturalGasGatheringOperationsMember
Litigation related to construction materials [Member]
Loss Contingencies [Line Items]
Loss contingency, estimate of possible loss						3,700,000us-gaap_LossContingencyEstimateOfPossibleLoss / us-gaap_LitigationCaseAxis = mdu_LitigationRelatedToConstructionMaterialsMember
Additional amount per day of potential penalties						5,000mdu_AdditionalAmountPerDayOfPotentialPenalties / us-gaap_LitigationCaseAxis = mdu_LitigationRelatedToConstructionMaterialsMember
Former employee litigation [Member]
Loss Contingencies [Line Items]
Plaintiffs request compensatory damages	23,800,000us-gaap_LossContingencyDamagesSoughtValue / us-gaap_LitigationCaseAxis = mdu_FormerEmployeeLitigationMemberMember
Litigation related to construction services [Member]
Loss Contingencies [Line Items]
Damage Repair Estimate							$ 26,000,000mdu_DamageRepairEstimate / us-gaap_LitigationCaseAxis = mdu_LitigationRelatedToConstructionServicesMember

X

- Definition

Additional amount per day of potential penalties.

+ References

No definition available.

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- Definition

Arbitration award.

+ References

No definition available.

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- Definition

Damage repair estimate for alleged defects.

+ References

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- Definition

Amount of loss contingency liability.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349

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- Definition

The value (monetary amount) of the award the plaintiff seeks in the legal matter.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 4

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14435-108349



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 9

-Subparagraph (a)

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- Definition

Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 4

-Subparagraph (b)

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