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Segment Information (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Segment Information
Upper limit of intersegment sales between the reportable segments	$ 0.1	$ 0.1

X

- Details

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

X

- 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