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Subsequent events Subsequesnt evenets (Details) - Subsequent event [Member] - USD ($) $ in Millions	Apr. 01, 2017	Apr. 25, 2017
Subsequent Event [Line Items]
Payments for repurchase of redeemable preferred stock	$ 15.9
Cascade Natural Gas Corporation [Member]
Subsequent Event [Line Items]
Line of credit facility, maximum borrowing capacity		$ 75.0
Intermountain Gas Company [Member]
Subsequent Event [Line Items]
Line of credit facility, maximum borrowing capacity		$ 85.0

X

- 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

X

- Definition

The cash outflow for reacquisition of callable preferred stock.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3291-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Financing Activities
-URI http://asc.fasb.org/extlink&oid=6513228

+ Details

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Balance Type:	credit
Period Type:	duration

X

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

+ Details

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Period Type:	duration

X

- Details

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X

- Details

Name:	dei_LegalEntityAxis=mdu_CascadeNaturalGasCorporationMember
Namespace Prefix:
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Balance Type:
Period Type:

X

- Details

Name:	dei_LegalEntityAxis=mdu_IntermountainGasCompanyMember
Namespace Prefix:
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Period Type: