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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

X

- 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

X

- Details

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