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Segment Information (Narrative) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2011 | Dec. 31, 2010 | Dec. 31, 2009
Revenue by Geographic Area, Major Customers and Segment Information |  |  |
Upper limit of intersegment sales between the reportable segments | $ 0.1 | $ 0.1 | $ 0.1

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

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- Definition Intersegment Sales Between The Reportable Segments + References No definition available. + Details
Name: | usu_IntersegmentSalesBetweenReportableSegments
Namespace Prefix: | usu_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration