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Subsquent event (Details) (USD $) In Millions, unless otherwise specified | 0 Months Ended
--- | ---
Mar. 31, 2014 | Jan. 28, 2014 The Company [Member] | Apr. 02, 2014 Subsequent event [Member] Centennial Energy Holdings, Inc [Member] | Jul. 15, 2014 Subsequent event [Member] The Company [Member] | Apr. 15, 2014 Subsequent event [Member] The Company [Member]
Subsequent Event [Line Items] |  |  |  |  |
Debt Instrument, Term | 2 years |  | 2 years |  |
Term loan agreement | $ 125.0 |  | $ 125.0 |  |
Note Purchase Agreement |  | 150.0 |  |  |
Senior Notes Issued |  |  |  |  | 50.0
Senior notes remained to be issued |  |  |  | $ 100.0 |
Senior notes weighted average interest rate |  |  |  | 4.30% | 5.20%

X
- Definition Note purchase agreement. + References No definition available. + Details
Name: | mdu_NotePurchaseAgreement
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Describes the event or transaction that occurred between the balance sheet date and the date the financial statements are issued or available to be issued. + References No definition available. + Details
Name: | mdu_SeniorNotesIssued
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | duration

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- Definition Senior notes remained to be issued. + References No definition available. + Details
Name: | mdu_Seniornotesremainedtobeissued
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Describes the event or transaction that occurred between the balance sheet date and the date the financial statements are issued or available to be issued. + References No definition available. + Details
Name: | mdu_SeniorNotesWeightedAverageInterestRate
Namespace Prefix: | mdu_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Term loan agreement. + References No definition available. + Details
Name: | mdu_Termloanagreement
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
Name: | us-gaap_DebtInstrumentTerm
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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