XML 52 R52.htm IDEA: XBRL DOCUMENT
v2.4.0.6

Revenue recognition (Details 7) (USD $) In Millions, unless otherwise specified | Dec. 31, 2012 | Dec. 31, 2011
--- | --- | ---
Revenue recognition [Abstract] |  |
Accrued unbilled revenue at Montana-Dakota, Cascade and Intermountain | $ 85.9 | $ 80.2

X
- Details
Name: | us-gaap_RevenueRecognitionAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The amount due for services rendered or products shipped, but not yet billed, recognized in conformity with revenue recognition criteria. This element is distinct from unbilled contracts receivables because this is based on noncontract transactions. + References No definition available. + Details
Name: | us-gaap_UnbilledReceivablesCurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant