Fair value measurements Assets (Details 4) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022	Jun. 30, 2022
Concentration risks, percentage [Abstract]
Percentage in fixed-income and other investments	67.00%	63.00%	64.00%
Percentage investment in common stock of large-cap companies	14.00%	15.00%	15.00%
Percentage investment in common stock of mid-cap companies	7.00%	8.00%	7.00%
Percentage investment in common stock of small-cap companies	6.00%	6.00%	6.00%
Percentage investment in target date investments	4.00%	6.00%	6.00%
Percentage investment in cash and cash equivalents	2.00%	2.00%	2.00%
Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	$ 346,840	$ 93,701	$ 94,256
Fair Value, Inputs, Level 1 \| Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	246,063
Fair value, inputs, level 2 \| Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	100,777	93,701	94,256
Investment in Knife River \| Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	246,063
Investment in Knife River \| Fair Value, Inputs, Level 1 \| Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	246,063
Money market funds \| Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	5,737	4,913	5,976
Money market funds \| Fair value, inputs, level 2 \| Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	5,737	4,913	5,976
Insurance contracts* \| Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	84,099	77,958	77,529
Insurance contracts* \| Fair value, inputs, level 2 \| Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	84,099	77,958	77,529
Mortgage-backed securities \| Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	7,891	8,294	7,709
Mortgage-backed securities \| Fair value, inputs, level 2 \| Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	7,891	8,294	7,709
U.S. Treasury securities \| Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	3,050	2,536	3,042
U.S. Treasury securities \| Fair value, inputs, level 2 \| Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	$ 3,050	$ 2,536	$ 3,042

Concentration Risks, Percentage

No definition available.

Name:	mdu_ConcentrationRisksPercentageAbstract
Namespace Prefix:	mdu_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The percentage of insurance contracts in fixed-income and other investments.

+ References

No definition available.

+ Details

Name:	mdu_PercentageInFixedIncomeAndOtherInvestments
Namespace Prefix:	mdu_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The percentage of insurance contracts in common stock of large-cap companies.

+ References

No definition available.

+ Details

Name:	mdu_PercentageInvestmentInCommonStockOfLargeCapCompanies
Namespace Prefix:	mdu_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The percentage of insurance contracts in common stock of mid-cap companies.

+ References

No definition available.

+ Details

Name:	mdu_PercentageInvestmentInCommonStockOfMidCapCompanies
Namespace Prefix:	mdu_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The percentage of insurance contracts in common stock of small-cap companies.

+ References

No definition available.

+ Details

Name:	mdu_PercentageInvestmentInCommonStockOfSmallCapCompanies
Namespace Prefix:	mdu_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of insurance contracts in cash and cash equivalents.

+ References

No definition available.

+ Details

Name:	mdu_PercentageInvestmentinCashandCashEquivalents
Namespace Prefix:	mdu_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The percentage of insurance contracts in target date investments.

+ References

No definition available.

+ Details

Name:	mdu_PercentageInvestmentinTargetDateInvestments
Namespace Prefix:	mdu_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-2

+ Details

Name:	us-gaap_AssetsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-2

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-3

+ Details

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

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsRecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=mdu_RetainedSharesInKnifeRiverMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_MoneyMarketFundsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_CashSurrenderValueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_MortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_USTreasurySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: