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v3.5.0.2

Guarantees (Details 3) | Sep. 30, 2016 USD ($)
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Guarantor Obligations [Line Items] |
Guarantor obligations, maximum exposure, undiscounted | $ 110,000,000
Fixed maximum amounts guaranteed by year 2016 | 4,200,000
Fixed maximum amounts guaranteed by year 2017 | 30,300,000
Fixed maximum amounts guaranteed by year 2018 | 12,000,000
Fixed maximum amounts guaranteed by year 2019 | 59,500,000
No scheduled maturity date | 4,000,000
Amount outstanding under guarantees that is reflected on balance sheet | 0
Letters of credit | 34,900,000
Letters of credit set to expire - 2016 | 2,900,000
Letters of credit set to expire - 2017 | 32,000,000
Outstanding letters of credit | 0
Amount of surety bonds outstanding | 560,700,000
Financial guarantee [Member] |
Guarantor Obligations [Line Items] |
Guarantor obligations, maximum exposure, undiscounted | $ 64,900,000

X
- Definition Amount of surety bonds outstanding related to construction contracts and reclamation obligations. + References No definition available. + Details
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Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The amount outstanding under gurantees that is reflected on the balance sheet. + References No definition available. + Details
Name: | mdu_AmountOutstandingUnderGuaranteesThatIsReflectedOnBalanceSheet
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Fixed maximum amounts guaranteed by year four. + References No definition available. + Details
Name: | mdu_FixedMaximumAmountsGuaranteedByYearFour
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Fixed maximum amounts guaranteed with no maturity date. + References No definition available. + Details
Name: | mdu_FixedMaximumAmountsGuaranteedByYearNoMaturityDate
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Fixed maximum amounts guaranteed by year one. + References No definition available. + Details
Name: | mdu_FixedMaximumAmountsGuaranteedByYearOne
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Fixed maximum amounts guaranteed by year three. + References No definition available. + Details
Name: | mdu_FixedMaximumAmountsGuaranteedByYearThree
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Fixed maximum amounts guaranteed by year two. + References No definition available. + Details
Name: | mdu_FixedMaximumAmountsGuaranteedByYearTwo
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
- Definition Letters of credit set to expire current year. + References No definition available. + Details
Name: | mdu_LettersofCreditSettoExpireCurrentYear
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Letters of credit set to expire in next fiscal year. + References No definition available. + Details
Name: | mdu_LettersofCreditSettoExpireinNextFiscalYear
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- 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_GuaranteeObligationsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 460 -SubTopic 10 -Section 50 -Paragraph 4 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=6851643&loc=d3e12069-110248 + Details
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Period Type: | instant

X
- Definition The total amount of the contingent obligation under letters of credit outstanding as of the reporting date. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
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Period Type: | instant

X
- Details
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