XML 59 R62.htm IDEA: XBRL DOCUMENT
v2.4.0.6

Discontinued operations (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2011
Arbitration charge related to a guarantee |  |  | $ 21.0
Arbitration charge after tax | $ (13.0) | $ 13.0 | $ 13.0

X
- Definition Arbitration charge after tax + References No definition available. + Details
Name: | mdu_ArbitrationChargeAfterTax
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Arbitration charge related to a guarantee + References No definition available. + Details
Name: | mdu_ArbitrationChargeRelatedToGuarantee
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration