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Long-term borrowings (Details 3) (Long-term debt [Member], USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Sep. 12, 2013
MDU Resources Group, Inc [Member] | Commercial paper revolving credit agreement [Member]
Debt instrument [Line Items]
Ratio of funded debt to capitalization - Company alone, as specified in debt convenants	65.00%
Ratio of funded debt to total capitalization as specified in debt convenants	65.00%
MDU Energy Capital, LLC [Member] | Master shelf agreement member [Member]
Debt instrument [Line Items]
Ratio of total debt to adjusted total capitalization as specified in debt convenants	70.00%
Ratio of subsidiary debt to subsidiary capitalization as specified in debt convenants	65.00%
Ratio of total debt to total capitalization as specified in debt convenants.	65.00%
Ratio - EBIT to interest expense	150.00%
MDU Energy Capital, LLC [Member] | Note purchase agreement [Member]
Debt instrument [Line Items]
Weighted average interest rate	5.30%
Contracted issuance of senior notes	$ 30.0
Intermountain Gas Company [Member] | Revolving credit agreement [Member]
Debt instrument [Line Items]
Ratio of total debt to total capitalization as specified in debt convenants.	65.00%
Centennial Energy Holdings, Inc [Member] | Revolving credit agreement [Member]
Debt instrument [Line Items]
Ratio of total debt to total capitalization as specified in debt convenants.	65.00%
Centennial Energy Holdings, Inc [Member] | Master shelf agreement member [Member]
Debt instrument [Line Items]
Ratio of total debt to total capitalization as specified in debt convenants.	60.00%
Ratio of EBITDA to interest expense	175.00%
WBI Energy Transmission, Inc. [Member] | Uncommitted long-term private shelf agreement [Member]
Debt instrument [Line Items]
Ratio of total debt to total capitalization as specified in debt convenants.	55.00%
Long-term private shelf agreement		175
Notes outstanding	$ 100.0

X

- Definition

Contracted issuance of senior notes.

+ References

No definition available.

+ Details

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X

- Definition

Long-term private shelf agreement.

+ References

No definition available.

+ Details

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X

- Definition

Notes outstanding which reduce capacity under the uncommitted private shelf agreement.

+ References

No definition available.

+ Details

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Balance Type:	credit
Period Type:	instant

X

- Definition

Ratio - EBITDA to interest expense.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	instant

X

- Definition

Ratio - EBIT to interest expense.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	instant

X

- Definition

Ratio of funded debt capitalization - Company alone, as specified in debt convenants.

+ References

No definition available.

+ Details

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X

- Definition

Ratio of funded debt to total capitalization as specified in debt convenants.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	instant

X

- Definition

Ratio of subsidiary debt to subsidiary capitalization as specified in debt convenants.

+ References

No definition available.

+ Details

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Namespace Prefix:	mdu_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Ratio of total debt to adjusted total capitalization as specified in debt convenants.

+ References

No definition available.

+ Details

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X

- Definition

Ratio of total debt to total capitalization as specified in debt convenants.

+ References

No definition available.

+ Details

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- Details

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X

- Definition

Weighted average interest rate of long-term debt outstanding.

+ References

No definition available.

+ Details

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