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Income Taxes (Details) (USD $) In Millions, unless otherwise specified | 6 Months Ended
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Jun. 30, 2013
Income Tax Expense (Benefit) [Abstract] |
Interim temporary timing difference in income tax calculation | $ 31.8

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- Details
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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
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Namespace Prefix: | usu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration