XML 140 R116.htm IDEA: XBRL DOCUMENT
v3.3.1.900

Variable interest entities (Details 6) - USD ($) | Dec. 31, 2015 | Sep. 30, 2015 | Dec. 31, 2014 | Dec. 01, 2014
--- | --- | --- | --- | ---
Dakota Prairie Refining, LLC [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Percent of ownership | 50.00% |  |  |
Total project costs | $ 300,000,000 |  |  |
Portion of capital commitment | 150,000,000 |  |  |
Partner portion of capital commitment | 75,000,000 |  |  |
Excess capital commitments | 300,000,000 |  |  |
Term loan for project debt financing | 75,000,000 |  |  |
Facility limit, maximum borrowing capacity |  | $ 75,000,000 |  | $ 50,000,000.0
Fuel contract [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Variable interest entity, reporting entity involvement, maximum loss exposure, amount | 40,100,000 |  |  |
Centennial Energy Holdings, Inc [Member] | Dakota Prairie Refining, LLC [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Percent of credit agreement guaranteed |  | 50.00% |  |
WBI Holdings [Member] | Dakota Prairie Refining, LLC [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Cumulative capital contributions, net of distributions | 230,400,000 |  |  |
Noncontrolling interest | Dakota Prairie Refining, LLC [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Cumulative capital contributions, net of distributions | 163,600,000 |  |  |
Percent of credit agreement guaranteed |  | 50.00% |  |
Cash and cash equivalents [Member] | Dakota Prairie Refining, LLC [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Variable interest entity, consolidated, carrying amount, assets | 851,000 |  | $ 21,376,000 |
Accounts receivable [Member] | Dakota Prairie Refining, LLC [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Variable interest entity, consolidated, carrying amount, assets | 7,693,000 |  | 2,759,000 |
Inventories [Member] | Dakota Prairie Refining, LLC [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Variable interest entity, consolidated, carrying amount, assets | 13,176,000 |  | 5,311,000 |
Other current assets [Member] | Dakota Prairie Refining, LLC [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Variable interest entity, consolidated, carrying amount, assets | 6,215,000 |  | 4,019,000 |
Total current assets [Member] | Dakota Prairie Refining, LLC [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Variable interest entity, consolidated, carrying amount, assets | 27,935,000 |  | 33,465,000 |
Net property, plant and equipment [Member] | Dakota Prairie Refining, LLC [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Variable interest entity, consolidated, carrying amount, assets | 425,123,000 |  | 398,984,000 |
Other [Member] | Dakota Prairie Refining, LLC [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Variable interest entity, consolidated, carrying amount, assets | 9,626,000 |  | 3,400,000 |
Total deferred charges and other assets [Member] | Dakota Prairie Refining, LLC [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Variable interest entity, consolidated, carrying amount, assets | 9,626,000 |  | 3,400,000 |
Total assets [Member] | Dakota Prairie Refining, LLC [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Variable interest entity, consolidated, carrying amount, assets | 462,684,000 |  | 435,849,000 |
Short-term borrowings [Member] | Dakota Prairie Refining, LLC [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Variable interest entity, consolidated, carrying amount, liabilities | 45,500,000 |  | 0 |
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 | 5,250,000 |  | 3,000,000 |
Accounts payable [Member] | Dakota Prairie Refining, LLC [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Variable interest entity, consolidated, carrying amount, liabilities | 24,766,000 |  | 55,089,000 |
Taxes payable [Member] | Dakota Prairie Refining, LLC [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Variable interest entity, consolidated, carrying amount, liabilities | 1,391,000 |  | 648,000 |
Accrued compensation [Member] | Dakota Prairie Refining, LLC [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Variable interest entity, consolidated, carrying amount, liabilities | 938,000 |  | 727,000 |
Other accrued liabilities [Member] | Dakota Prairie Refining, LLC [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Variable interest entity, consolidated, carrying amount, liabilities | 4,953,000 |  | 899,000 |
Total current liabilities [Member] | Dakota Prairie Refining, LLC [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Variable interest entity, consolidated, carrying amount, liabilities | 82,798,000 |  | 60,363,000 |
Long-term debt [Member] | Dakota Prairie Refining, LLC [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Variable interest entity, consolidated, carrying amount, liabilities | 63,750,000 |  | 69,000,000 |
Total liabilities [Member] | Dakota Prairie Refining, LLC [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Variable interest entity, consolidated, carrying amount, liabilities | $ 146,548,000 |  | $ 129,363,000 |

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 General partners capital contributions, net of distributions. + References No definition available. + Details
Name: | mdu_GeneralPartnersCapitalContributionsNetofDistributions
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 ownership. + References No definition available. + Details
Name: | mdu_PercentOfOwnership
Namespace Prefix: | mdu_
Data Type: | num:percentItemType
Balance Type: | na
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 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 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 + 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=52262685&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=52262685&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=52262685&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=52262685&loc=d3e5747-111685 + Details
Name: | us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount
Namespace Prefix: | us-gaap_
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_VariableInterestEntityLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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: |

X
- Details
Name: | us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=mdu_CentennialEnergyHoldingsIncMember
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_BalanceSheetLocationAxis=us-gaap_CashAndCashEquivalentsMember
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_InventoriesMember
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=mdu_TotalCurrentAssetsMember
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=us-gaap_OtherNoncurrentAssetsMember
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=us-gaap_AssetsTotalMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_BalanceSheetLocationAxis=us-gaap_ShortTermDebtMember
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=us-gaap_AccountsPayableMember
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_AccruedCompensationMember
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_TotalcurrentliabilitiesMember
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=mdu_TotalLiabilitiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |