XML 86 R61.htm IDEA: XBRL DOCUMENT
v2.4.0.8

Litigation (Details) (USD $) | Sep. 30, 2013 | Dec. 31, 2012 | Sep. 30, 2012 | Aug. 31, 2011 Litigation related to construction materials [Member] | Jun. 30, 2013 Natural gas gathering operations [Member] | Jun. 30, 2012 Natural gas gathering operations [Member] | Oct. 31, 2010 Natural gas gathering operations [Member] | Sep. 30, 2010 Natural gas gathering operations [Member] | Jan. 13, 2012 Guarantee obligation under construction contract [Member] | Dec. 31, 2009 Guarantee obligation under construction contract [Member]
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |
Potential liabilities related to litigation and environmental matters | $ 30,800,000 | $ 22,500,000 | $ 41,600,000 |  |  |  |  |  |  |
Amount of compensatory damages in LPP's notice of demand |  |  |  |  |  |  |  |  |  | 149,700,000
Arbitration award |  |  |  |  |  |  | 26,600,000 |  | 22,000,000 |
Estimated damages in pending litigation, low estimate |  |  |  |  | 16,100,000 |  |  |  |  |
Estimated damages in pending litigation, high estimate |  |  |  |  | 22,600,000 |  |  |  |  |
Loss contingency, estimate of possible loss |  |  |  | 3,700,000 |  |  |  |  |  |
Additional amount per day of potential penalties |  |  |  | 5,000 |  |  |  |  |  |
Amount of expense (benefit) recorded in operation and maintenance expense related to natural gas gathering contract dispute, before tax |  |  |  |  |  | (24,100,000) |  | 26,600,000 |  |
Amount of expense (benefit) recorded in operation and maintenance expense related to natural gas gathering contract dispute, after tax |  |  |  |  |  | (15,000,000) |  | 16,500,000 |  |
Revised damage calculation |  |  |  |  | $ 1,000,000 |  |  |  |  |

X
- Definition Additional amount per day of potential penalties. + References No definition available. + Details
Name: | mdu_AdditionalAmountPerDayOfPotentialPenalties
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of compensatory damages in notice of demand related to the construction contract litigation. + References No definition available. + Details
Name: | mdu_AmountOfCompensatoryDamagesInDemandNotice
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of expense (benefit) recorded in operation and maintenance expense related to natural gas gathering contract dispute, after tax. + References No definition available. + Details
Name: | mdu_AmountOfExpenseBenefitRecordedInOperationAndMaintenanceExpenseRelatedToNaturalGasGatheringContractDisputeAfterTax
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of expense (benefit) recorded in operation and maintenance expense related to natural gas gathering contract dispute, before tax. + References No definition available. + Details
Name: | mdu_AmountOfExpenseBenefitRecordedInOperationAndMaintenanceExpenseRelatedToNaturalGasGatheringContractDisputeBeforeTax
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Arbitration award. + References No definition available. + Details
Name: | mdu_ArbitrationAward
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The amount accrued for potential liabilities related to litigation and enviromental matters as of the balance sheet date. + References No definition available. + Details
Name: | mdu_PotentialLiabilitiesRelatedToLitigationAndEnvironmentalMatters
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Revised damage calculation. + References No definition available. + Details
Name: | mdu_RevisedDamageCalculation
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

X
- Definition Reflects the estimated amount of loss from the specified contingency as of the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14435-108349 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 9 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14557-108349 + Details
Name: | us-gaap_LossContingencyEstimateOfPossibleLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The estimated maximum amount of possible loss from the contingency. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14435-108349 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 9 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14557-108349 + Details
Name: | us-gaap_LossContingencyRangeOfPossibleLossMaximum
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The estimated minimum amount of possible loss from the contingency. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14435-108349 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 9 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14557-108349 + Details
Name: | us-gaap_LossContingencyRangeOfPossibleLossMinimum
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant