XML 134 R115.htm IDEA: XBRL DOCUMENT v2.4.1.9

Variable interest entities (Details 6) (USD $)	Dec. 31, 2014	Dec. 01, 2014	Dec. 31, 2013
Dakota Prairie Refining, LLC [Member]
Variable Interest Entities [Line Items]
Percent of ownership	50.00%mdu_PercentOfOwnership / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember
Total project costs	$ 300,000,000mdu_Totalprojectcosts / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember
Portion of capital commitment	150,000,000mdu_PortionOfCapitalCommitment / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember
Partner portion of capital commitment	75,000,000mdu_PartnerPortionOfCapitalCommitment / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember
Excess capital commitments	300,000,000mdu_ExcessCapitalCommitments / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember
Estimated project cost	400,000,000mdu_ProjectCostEstimate / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember
Term loan for project debt financing	75,000,000mdu_TermLoanForProjectDebtFinancing / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember
Facility limit, maximum borrowing capacity		50,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember
Fuel contract [Member]
Variable Interest Entities [Line Items]
Variable interest entity, reporting entity involvement, maximum loss exposure, amount	15,800,000us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_FuelContractMember
WBI Holdings [Member] | Dakota Prairie Refining, LLC [Member]
Variable Interest Entities [Line Items]
Percent of credit agreement guaranteed		50.00%mdu_PercentofCreditAgreementGuaranteed / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = mdu_WBIHoldingsMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember
Noncontrolling interest | Dakota Prairie Refining, LLC [Member]
Variable Interest Entities [Line Items]
Percent of credit agreement guaranteed		50.00%mdu_PercentofCreditAgreementGuaranteed / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = us-gaap_NoncontrollingInterestMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember
Cash and cash equivalents [Member] | Dakota Prairie Refining, LLC [Member]
Variable Interest Entities [Line Items]
Variable interest entity, consolidated, carrying amount, assets	21,376,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets / us-gaap_BalanceSheetLocationAxis = us-gaap_CashAndCashEquivalentsMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember		4,774,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets / us-gaap_BalanceSheetLocationAxis = us-gaap_CashAndCashEquivalentsMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember
Accounts receivable [Member] | Dakota Prairie Refining, LLC [Member]
Variable Interest Entities [Line Items]
Variable interest entity, consolidated, carrying amount, assets	2,759,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets / us-gaap_BalanceSheetLocationAxis = us-gaap_AccountsReceivableMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember		0us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets / us-gaap_BalanceSheetLocationAxis = us-gaap_AccountsReceivableMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember
Inventories [Member] | Dakota Prairie Refining, LLC [Member]
Variable Interest Entities [Line Items]
Variable interest entity, consolidated, carrying amount, assets	5,311,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets / us-gaap_BalanceSheetLocationAxis = us-gaap_InventoriesMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember		0us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets / us-gaap_BalanceSheetLocationAxis = us-gaap_InventoriesMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember
Other current assets [Member] | Dakota Prairie Refining, LLC [Member]
Variable Interest Entities [Line Items]
Variable interest entity, consolidated, carrying amount, assets	4,019,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherCurrentAssetsMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember		26,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherCurrentAssetsMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember
Total current assets [Member] | Dakota Prairie Refining, LLC [Member]
Variable Interest Entities [Line Items]
Variable interest entity, consolidated, carrying amount, assets	33,465,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets / us-gaap_BalanceSheetLocationAxis = mdu_TotalCurrentAssetsMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember		4,800,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets / us-gaap_BalanceSheetLocationAxis = mdu_TotalCurrentAssetsMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember
Net property, plant and equipment [Member] | Dakota Prairie Refining, LLC [Member]
Variable Interest Entities [Line Items]
Variable interest entity, consolidated, carrying amount, assets	398,984,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets / us-gaap_BalanceSheetLocationAxis = mdu_NetPropertyPlantAndEquipmentMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember		172,073,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets / us-gaap_BalanceSheetLocationAxis = mdu_NetPropertyPlantAndEquipmentMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember
Other [Member] | Dakota Prairie Refining, LLC [Member]
Variable Interest Entities [Line Items]
Variable interest entity, consolidated, carrying amount, assets	3,400,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherNoncurrentAssetsMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember		0us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherNoncurrentAssetsMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember
Total deferred charges and other assets [Member] | Dakota Prairie Refining, LLC [Member]
Variable Interest Entities [Line Items]
Variable interest entity, consolidated, carrying amount, assets	3,400,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets / us-gaap_BalanceSheetLocationAxis = mdu_TotalDeferredChargesandOtherAssetsMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember		0us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets / us-gaap_BalanceSheetLocationAxis = mdu_TotalDeferredChargesandOtherAssetsMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember
Total assets [Member] | Dakota Prairie Refining, LLC [Member]
Variable Interest Entities [Line Items]
Variable interest entity, consolidated, carrying amount, assets	435,849,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets / us-gaap_BalanceSheetLocationAxis = us-gaap_AssetsTotalMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember		176,873,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets / us-gaap_BalanceSheetLocationAxis = us-gaap_AssetsTotalMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember
Long-term debt due within one year [Member] | Dakota Prairie Refining, LLC [Member]
Variable Interest Entities [Line Items]
Variable interest entity, consolidated, carrying amount, liabilities	3,000,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountLiabilities / us-gaap_BalanceSheetLocationAxis = mdu_LongtermdebtduewithinoneyearMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember		3,000,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountLiabilities / us-gaap_BalanceSheetLocationAxis = mdu_LongtermdebtduewithinoneyearMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember
Accounts payable [Member] | Dakota Prairie Refining, LLC [Member]
Variable Interest Entities [Line Items]
Variable interest entity, consolidated, carrying amount, liabilities	55,089,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountLiabilities / us-gaap_BalanceSheetLocationAxis = us-gaap_AccountsPayableMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember		8,904,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountLiabilities / us-gaap_BalanceSheetLocationAxis = us-gaap_AccountsPayableMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember
Taxes payable [Member] | Dakota Prairie Refining, LLC [Member]
Variable Interest Entities [Line Items]
Variable interest entity, consolidated, carrying amount, liabilities	648,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountLiabilities / us-gaap_BalanceSheetLocationAxis = mdu_TaxesPayableMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember		5,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountLiabilities / us-gaap_BalanceSheetLocationAxis = mdu_TaxesPayableMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember
Accrued compensation [Member] | Dakota Prairie Refining, LLC [Member]
Variable Interest Entities [Line Items]
Variable interest entity, consolidated, carrying amount, liabilities	727,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountLiabilities / us-gaap_BalanceSheetLocationAxis = mdu_AccruedCompensationMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember		26,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountLiabilities / us-gaap_BalanceSheetLocationAxis = mdu_AccruedCompensationMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember
Other accrued liabilities [Member] | Dakota Prairie Refining, LLC [Member]
Variable Interest Entities [Line Items]
Variable interest entity, consolidated, carrying amount, liabilities	899,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountLiabilities / us-gaap_BalanceSheetLocationAxis = mdu_OtherAccruedLiabilitiesMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember		461,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountLiabilities / us-gaap_BalanceSheetLocationAxis = mdu_OtherAccruedLiabilitiesMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember
Total current liabilities [Member] | Dakota Prairie Refining, LLC [Member]
Variable Interest Entities [Line Items]
Variable interest entity, consolidated, carrying amount, liabilities	60,363,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountLiabilities / us-gaap_BalanceSheetLocationAxis = mdu_TotalcurrentliabilitiesMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember		12,396,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountLiabilities / us-gaap_BalanceSheetLocationAxis = mdu_TotalcurrentliabilitiesMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember
Long-term debt [Member] | Dakota Prairie Refining, LLC [Member]
Variable Interest Entities [Line Items]
Variable interest entity, consolidated, carrying amount, liabilities	69,000,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountLiabilities / us-gaap_BalanceSheetLocationAxis = us-gaap_LongTermDebtMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember		72,000,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountLiabilities / us-gaap_BalanceSheetLocationAxis = us-gaap_LongTermDebtMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember
Total liabilities [Member] | Dakota Prairie Refining, LLC [Member]
Variable Interest Entities [Line Items]
Variable interest entity, consolidated, carrying amount, liabilities	$ 129,363,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountLiabilities / us-gaap_BalanceSheetLocationAxis = mdu_TotalLiabilitiesMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember		$ 84,396,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountLiabilities / us-gaap_BalanceSheetLocationAxis = mdu_TotalLiabilitiesMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = mdu_DakotaPrairieRefiningLlcMember

X

- Definition

Excess capital commitments above this amount will be shared equally.

+ References

No definition available.

+ Details

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

X

- Definition

Partner portion of capital commitment.

+ References

No definition available.

+ Details

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

X

- Definition

Percent of credit agreement guaranteed.

+ References

No definition available.

+ Details

Name:	mdu_PercentofCreditAgreementGuaranteed
Namespace Prefix:	mdu_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Percent of ownership.

+ References

No definition available.

+ Details

Name:	mdu_PercentOfOwnership
Namespace Prefix:	mdu_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Portion of capital commitment.

+ References

No definition available.

+ Details

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

X

- Definition

Project cost estimate

+ References

No definition available.

+ Details

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

X

- Definition

Amount of term loan entered into to finance the project.

+ References

No definition available.

+ Details

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

X

- Definition

Total project costs.

+ References

No definition available.

+ Details

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

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



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

+ Details

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

X

- Definition

The carrying amount of the consolidated Variable Interest Entity's assets included in the reporting entity's statement of financial position.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 810

-SubTopic 10

-Section 50

-Paragraph 3

-Subparagraph (bb)

-URI http://asc.fasb.org/extlink&oid=28200181&loc=d3e5710-111685

+ Details

Name:	us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

The carrying amount of the consolidated Variable Interest Entity's liabilities included in the reporting entity's statement of financial position.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 810

-SubTopic 10

-Section 50

-Paragraph 3

-Subparagraph (bb)

-URI http://asc.fasb.org/extlink&oid=28200181&loc=d3e5710-111685

+ Details

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

X

- Definition

The reporting entity's maximum amount of exposure to loss as a result of its involvement with the Variable Interest Entity (VIE).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 810

-SubTopic 10

-Section 50

-Paragraph 4

-Subparagraph b

-URI http://asc.fasb.org/extlink&oid=28200181&loc=d3e5728-111685



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 810

-SubTopic 10

-Section 50

-Paragraph 6

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=28200181&loc=d3e5747-111685

+ Details

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

X

- Details

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

X

- Details

Name:	us-gaap_BalanceSheetLocationAxis=mdu_AccruedCompensationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_BalanceSheetLocationAxis=mdu_LongtermdebtduewithinoneyearMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_BalanceSheetLocationAxis=mdu_NetPropertyPlantAndEquipmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_BalanceSheetLocationAxis=mdu_OtherAccruedLiabilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_BalanceSheetLocationAxis=mdu_TaxesPayableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_BalanceSheetLocationAxis=mdu_TotalCurrentAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_BalanceSheetLocationAxis=mdu_TotalcurrentliabilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_BalanceSheetLocationAxis=mdu_TotalDeferredChargesandOtherAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_BalanceSheetLocationAxis=mdu_TotalLiabilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_AccountsPayableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_AccountsReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_AssetsTotalMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_CashAndCashEquivalentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_InventoriesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_LongTermDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherCurrentAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherNoncurrentAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=mdu_WBIHoldingsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=us-gaap_NoncontrollingInterestMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis=mdu_DakotaPrairieRefiningLlcMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis=mdu_FuelContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: