XML 122 R58.htm IDEA: XBRL DOCUMENT
v2.4.0.6

Derivative Instruments (Details) (USD $) | 12 Months Ended
--- | ---
Dec. 31, 2011 MMBTU bbl | Dec. 31, 2010
Derivative Instruments [Line Items] |  |
Natural gas swap agreement with total foward notional volumes | 305,000 |
Change In Fair Value Of Derivative Instruments Not Designated As Hedging Instruments Recorded As Increase Decrease To Regulatory Assets | $ 8,900,000 | $ 18,500,000
Aggregate fair value of Assets Needed for Immediate Settlement if credit-risk related contingent features were triggered | 437,000 |
Derivative instruments with credit-risk-related contingent features, net liability position, aggregate fair value | 437,000 |
Nonmonetary Notional Forward Amount of natural gas swap, collar and/or put agreements in MMBtu, Derivative Instruments Designated as cash flow hedging Instruments | 10,800,000 |
Notional Forward Amount Of Cash Flow Hedge Instruments Natural Gas Basis Swaps | 3,500,000 |
Notional Forward Amount Of Cash Flow Hedge Instruments Oil Swaps And Collars | 4,000,000 |
Notional Amount of Derivatives | 60,000,000 |
Maximum length of time hedged in swap, collar and/or put cash flow hedge agreements (in months) | 24 |
Amount of Hedge Ineffectiveness | 1,800,000 |
Cash flow hedge gain (loss) to be reclassified within twelve months from AOCI into earnings | 8,700,000 |
Derivative Net Liability Position Aggregate Fair Value For Cash Flow Hedging Instruments | 18,400,000 |
Assets Needed For Immediate Settlement Aggregate Fair Value For Cash Flow Hedging Instruments | $ 18,400,000 |

X
- Definition Amount of hedge ineffectiveness + References No definition available. + Details
Name: | mdu_AmountOfHedgeIneffectiveness
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | duration

X
- Definition The aggregate fair value of assets needed to immediately settle the derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period for cash flow hedging instruments + References No definition available. + Details
Name: | mdu_AssetsNeededForImmediateSettlementAggregateFairValueForCashFlowHedingInstruments
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Change in fair value of derivative instruments not designated as hedging instruments recorded as an increase (decrease) to regulatory assets + References No definition available. + Details
Name: | mdu_ChangeInFairValueOfDerivativeInstrumentsNotDesignatedAsHedgingInstrumentsRecordedAsIncreaseDecreaseToRegulatoryAssets
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The aggregate fair value amounts of derivative instruments that contain credit-risk-related contingent features that are in a net liability position at the end of the reporting period. For nonderivative instruments that are designated and qualify as cash flow hedging instruments, the fair value amounts are the carrying value of the nonderivative hedging instrument, including the adjustment for the foreign currency transaction gain or loss on that instrument. + References No definition available. + Details
Name: | mdu_DerivativeNetLiabilityPositionAggregateFairValueForCashFlowHedgingInstruments
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Natural gas swap agreement with total foward notional volumes + References No definition available. + Details
Name: | mdu_NaturalGasSwapAgreementWithTotalFowardNotionalVolumes
Namespace Prefix: | mdu_
Data Type: | num:energyItemType
Balance Type: | na
Period Type: | duration

X
- Definition Nonmonetary notional forward amount of natural gas swap, collar and or put agreements in MMBtu, derivative instruments designated as cash flow hedging instruments + References No definition available. + Details
Name: | mdu_NonmonetaryNotionalForwardAmountOfNaturalGasSwapColarAndOrPutAgreementsInMmbtuDerivativeInstrumentsDesignatedAsCashFlowHedgingInstruments
Namespace Prefix: | mdu_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

X
- Definition Nonmonetary Notional forward Amount of natural gas basis swap agreements in MMBtu, Derivative Instruments Designated as cash flow hedging Instruments + References No definition available. + Details
Name: | mdu_NotionalForwardAmountOfCashFlowHedgeInstrumentsNaturalGasBasisSwaps
Namespace Prefix: | mdu_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

X
- Definition Nonmonetary Notional forward Amount of oil swap, collar and/or put agreements in Bbl, Derivative Instruments Designated as cash flow hedging Instruments + References No definition available. + Details
Name: | mdu_NotionalForwardAmountOfCashFlowHedgeInstrumentsOilSwapsAndCollars
Namespace Prefix: | mdu_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

X
- Definition The aggregate fair value of assets needed to immediately settle the derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4H -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5624258-113959 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 44D -Subparagraph c -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
Name: | us-gaap_AssetsNeededForImmediateSettlementAggregateFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 45 -Subparagraph b(2) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6887037&loc=d3e80748-113994 + Details
Name: | us-gaap_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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

X
- Definition The aggregate fair value amounts of derivative instruments that contain credit-risk-related contingent features that are in a net liability position at the end of the reporting period. For nonderivative instruments that are designated and qualify as hedging instruments, the fair value amounts are the carrying value of the nonderivative hedging instrument, including the adjustment for the foreign currency transaction gain (loss) on that instrument. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4H -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5624258-113959 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 44D -Subparagraph b -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
Name: | us-gaap_DerivativeNetLiabilityPositionAggregateFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Maximum length of time over which the entity is hedging its exposure to the variability in future cash flows for forecasted transactions, excluding those forecasted transactions related to the payment of variable interest on existing financial instruments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 45 -Subparagraph b(3) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=6887037&loc=d3e80748-113994 + Details
Name: | us-gaap_MaximumLengthOfTimeHedgedInCashFlowHedge
Namespace Prefix: | us-gaap_
Data Type: | us-types:durationStringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Aggregate notional amount of interest rate derivatives, which relates to the currency amount specified in the interest rate derivative instruments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1B -URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5580258-113959 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Notional Amount -URI http://asc.fasb.org/extlink&oid=6519104 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1A -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5579245-113959 + Details
Name: | us-gaap_NotionalAmountOfInterestRateDerivatives
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant