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Preferred Stocks (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Class of Stock [Line Items]
Preferred stock redemption price upon liquidation (in dollars per share)	$ 100us-gaap_PreferredStockRedemptionPricePerShare
Preferred stocks	$ 15,000us-gaap_PreferredStockValue	$ 15,000us-gaap_PreferredStockValue
Cumulative Preferred Stock, Par Value $100 Issuable in Series [Member]
Class of Stock [Line Items]
Authorized preferred cumulative shares (in shares)	500,000us-gaap_PreferredStockSharesAuthorized / us-gaap_StatementClassOfStockAxis = mdu_PreferredStockWithParValueMember	500,000us-gaap_PreferredStockSharesAuthorized / us-gaap_StatementClassOfStockAxis = mdu_PreferredStockWithParValueMember
Cumulative preferred shares, par value (in dollars per share)	$ 100.00us-gaap_PreferredStockParOrStatedValuePerShare / us-gaap_StatementClassOfStockAxis = mdu_PreferredStockWithParValueMember	$ 100.00us-gaap_PreferredStockParOrStatedValuePerShare / us-gaap_StatementClassOfStockAxis = mdu_PreferredStockWithParValueMember
Preferred stock, series 4.50% [Member]
Class of Stock [Line Items]
Preferred stock redemption price at the option of the company (in dollars per share)	$ 105mdu_PreferredStockRedemptionPriceOptionOfCompany / us-gaap_StatementClassOfStockAxis = mdu_PreferredStockSeries45Member
Preferred stocks	10,000us-gaap_PreferredStockValue / us-gaap_StatementClassOfStockAxis = mdu_PreferredStockSeries45Member	10,000us-gaap_PreferredStockValue / us-gaap_StatementClassOfStockAxis = mdu_PreferredStockSeries45Member
Preferred shares outstanding (in shares)	100,000us-gaap_PreferredStockSharesOutstanding / us-gaap_StatementClassOfStockAxis = mdu_PreferredStockSeries45Member	100,000us-gaap_PreferredStockSharesOutstanding / us-gaap_StatementClassOfStockAxis = mdu_PreferredStockSeries45Member
Preferred stock, $100 par value	4.50%us-gaap_PreferredStockDividendRatePercentage / us-gaap_StatementClassOfStockAxis = mdu_PreferredStockSeries45Member	4.50%us-gaap_PreferredStockDividendRatePercentage / us-gaap_StatementClassOfStockAxis = mdu_PreferredStockSeries45Member	4.50%us-gaap_PreferredStockDividendRatePercentage / us-gaap_StatementClassOfStockAxis = mdu_PreferredStockSeries45Member
Preferred stock, dividends per share, declared	$ 4.50us-gaap_PreferredStockDividendsPerShareDeclared / us-gaap_StatementClassOfStockAxis = mdu_PreferredStockSeries45Member	$ 4.50us-gaap_PreferredStockDividendsPerShareDeclared / us-gaap_StatementClassOfStockAxis = mdu_PreferredStockSeries45Member	$ 4.50us-gaap_PreferredStockDividendsPerShareDeclared / us-gaap_StatementClassOfStockAxis = mdu_PreferredStockSeries45Member
Preferred stock, series 4.70% [Member]
Class of Stock [Line Items]
Preferred stock redemption price at the option of the company (in dollars per share)	$ 102mdu_PreferredStockRedemptionPriceOptionOfCompany / us-gaap_StatementClassOfStockAxis = mdu_PreferredStockSeries470Member
Preferred stocks	$ 5,000us-gaap_PreferredStockValue / us-gaap_StatementClassOfStockAxis = mdu_PreferredStockSeries470Member	$ 5,000us-gaap_PreferredStockValue / us-gaap_StatementClassOfStockAxis = mdu_PreferredStockSeries470Member
Preferred shares outstanding (in shares)	50,000us-gaap_PreferredStockSharesOutstanding / us-gaap_StatementClassOfStockAxis = mdu_PreferredStockSeries470Member	50,000us-gaap_PreferredStockSharesOutstanding / us-gaap_StatementClassOfStockAxis = mdu_PreferredStockSeries470Member
Preferred stock, $100 par value	4.70%us-gaap_PreferredStockDividendRatePercentage / us-gaap_StatementClassOfStockAxis = mdu_PreferredStockSeries470Member	4.70%us-gaap_PreferredStockDividendRatePercentage / us-gaap_StatementClassOfStockAxis = mdu_PreferredStockSeries470Member	4.70%us-gaap_PreferredStockDividendRatePercentage / us-gaap_StatementClassOfStockAxis = mdu_PreferredStockSeries470Member
Preferred stock, dividends per share, declared	$ 4.70us-gaap_PreferredStockDividendsPerShareDeclared / us-gaap_StatementClassOfStockAxis = mdu_PreferredStockSeries470Member	$ 4.70us-gaap_PreferredStockDividendsPerShareDeclared / us-gaap_StatementClassOfStockAxis = mdu_PreferredStockSeries470Member	$ 4.70us-gaap_PreferredStockDividendsPerShareDeclared / us-gaap_StatementClassOfStockAxis = mdu_PreferredStockSeries470Member
Cumulative preferred stock A, without par value, issuable in series [Member]
Class of Stock [Line Items]
Authorized preferred cumulative shares (in shares)	1,000,000us-gaap_PreferredStockSharesAuthorized / us-gaap_StatementClassOfStockAxis = us-gaap_PreferredClassAMember	1,000,000us-gaap_PreferredStockSharesAuthorized / us-gaap_StatementClassOfStockAxis = us-gaap_PreferredClassAMember
Cumulative preference stock , without par value, issuable in series [Member]
Class of Stock [Line Items]
Authorized preferred cumulative shares (in shares)	500,000us-gaap_PreferredStockSharesAuthorized / us-gaap_StatementClassOfStockAxis = mdu_PreferenceStockMember	500,000us-gaap_PreferredStockSharesAuthorized / us-gaap_StatementClassOfStockAxis = mdu_PreferenceStockMember

X

- Definition

The redemption price per share at which the preferred stock of an entity that has priority over common stock in the distribution of dividends may be redeemed at the option of the company with certain limitation

+ References

No definition available.

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- Definition

The percentage rate used to calculate dividend payments on preferred stock.

+ References

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- Definition

Aggregate dividends declared during the period for each share of preferred stock outstanding.

+ References

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- Definition

Face amount or stated value per share of preferred stock nonredeemable or redeemable solely at the option of the issuer.

+ 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 210.5-02.28)

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-Section 02

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- Definition

The price per share at which the preferred stock of an entity that has priority over common stock in the distribution of dividends and in the event of liquidation of the entity is redeemed or may be called at. The redemption features of this preferred stock are solely within the control of the issuer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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-SubTopic 10

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- Definition

The maximum number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) permitted to be issued by an entity's charter and bylaws.

+ References

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- Definition

Aggregate share number for all nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) held by stockholders. Does not include preferred shares that have been repurchased.

+ References

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- Definition

Aggregate par or stated value of issued nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer). This item includes treasury stock repurchased by the entity. Note: elements for number of nonredeemable preferred shares, par value and other disclosure concepts are in another section within stockholders' equity.

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