Long-term debt (Details) - Centennial Energy Holdings, Inc [Member] $ in Millions	Sep. 23, 2016 USD ($)
Line of Credit Facility [Line Items]
Facility, decrease borrowing capacity	$ 150.0
Facility, maximum borrowing capacity	$ 500.0
Ratio of total debt to total capitalization as specified in debt convenants.	65.00%

Decrease in maximum borrowing capacity for debt instruments.

No definition available.

Name:	mdu_LineofCreditFacilityDecreaseBorrowingCapacity
Namespace Prefix:	mdu_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- 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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	dei_LegalEntityAxis=mdu_CentennialEnergyHoldingsIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: