XML 70 R53.htm IDEA: XBRL DOCUMENT
v2.4.0.6

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

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