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Commitments and contingencies - Guarantees (Details)	Mar. 31, 2025 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Letters of credit	$ 14,000,000
Outstanding letters of credit	0
Amount of surety bonds outstanding	$ 15,600,000

X

- Definition

Amount of surety bonds outstanding related to construction contracts and reclamation obligations.

+ References

No definition available.

+ Details

Name:	mdu_AmountOfSuretyBondsOutstanding
Namespace Prefix:	mdu_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Letters of credit.

+ References

No definition available.

+ Details

Name:	mdu_LettersOfCredit
Namespace Prefix:	mdu_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- References

No definition available.

+ Details

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

X

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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