XML 131 R115.htm IDEA: XBRL DOCUMENT
v2.4.0.6

Commitments and Contingencies Variable interest entities (Details) | Dec. 31, 2012
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Entity Information [Line Items] |
Percent of ownership | 25.00%

X
- Details
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Namespace Prefix: | dei_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percent of ownership. + References No definition available. + Details
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Namespace Prefix: | mdu_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant