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Income Taxes (Details) (USD $) In Millions, unless otherwise specified | 9 Months Ended
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Sep. 30, 2013
Income Tax Disclosure [Abstract] |
Interim temporary timing difference in income tax calculation | $ 14.9

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

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- Definition Interim temporary timing difference in income tax calculation + References No definition available. + Details
Name: | usu_InterimTemporaryTimingDifferenceInIncomeTaxCalculation
Namespace Prefix: | usu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration