Public Utilities, Approved Rate Increase (Decrease) For Excess Deferred Income Taxes, Amount

No definition available.

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

- Definition

Public Utilities, Approved Rate Increase (Decrease) For Tax Benefits, Amount

+ References

No definition available.

+ Details

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

- Definition

Amount of public utility's approved rate increase (decrease) by regulatory agency.

+ References

No definition available.

+ Details

Name:	us-gaap_PublicUtilitiesApprovedRateIncreaseDecreaseAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Percentage of public utility's approved rate increase (decrease) by regulatory agency.

+ References

No definition available.

+ Details

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

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

- Definition

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

+ References

No definition available.

+ Details

Name:	us-gaap_PublicUtilitiesRequestedRateIncreaseDecreaseAmendedAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

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

+ References

No definition available.

+ Details

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

- Definition

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

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_RegulatoryAgencyAxis=mdu_WUTCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PublicUtilitiesRegulatoryProceedingAxis=mdu_NaturalgasrateproceedingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeTaxAuthorityAxis=mdu_TaxCutsandJobsActMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PublicUtilitiesRegulatoryProceedingAxis=mdu_PipelineReplacementCostRecoveryMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Washington Utilities and Transportation Commission (WUTC) (Details 5) - WUTC - USD ($) $ in Millions	Oct. 11, 2018	Jul. 20, 2018	Jun. 01, 2018	Mar. 23, 2018	Aug. 31, 2017
Natural gas rate proceeding
Public Utilities, General Disclosures [Line Items]
Public utilities, requested rate increase (decrease), amount					$ 5.9
Public utilities, requested rate increase (decrease), percentage					2.70%
Natural gas rate proceeding \| Tax Cuts and Jobs Act
Public Utilities, General Disclosures [Line Items]
Public utilities, requested rate increase (decrease), amended, amount				$ (1.7)
Public Utilities, Approved Rate Increase (Decrease), Amount		$ (2.9)
Public utilities, approved rate increase (decrease), percentage		(1.40%)
Public Utilities, Approved Rate Increase (Decrease) For Excess Deferred Income Taxes, Amount		$ (2.5)
Public Utilities, Approved Rate Increase (Decrease) For Tax Benefits, Amount		$ (1.6)
Pipeline replacement cost recovery
Public Utilities, General Disclosures [Line Items]
Public utilities, requested rate increase (decrease), amount			$ 2.3
Public utilities, requested rate increase (decrease), percentage			1.10%
Pipeline replacement cost recovery \| Subsequent Event
Public Utilities, General Disclosures [Line Items]
Public utilities, requested rate increase (decrease), amount	$ 2.1
Public utilities, requested rate increase (decrease), percentage	1.00%