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Net Income Per Share (Options and Warrants Excluded From the Calculation) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified | 12 Months Ended
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Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010
Stock Options [Member] |  |  |
Options excluded from diluted earnings per share | 2.5 | 3.1 | 2.5
Warrants [Member] |  |  |
Warrants excluded from diluted earnings per share | 6.3 | 6.3 | 2.1
Maximum [Member] | Stock Options [Member] |  |  |
Exercise price of excluded options | 14.28 | 14.28 | 14.28
Minimum [Member] | Stock Options [Member] |  |  |
Exercise price of excluded options | 3.72 | 3.72 | 5.18

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- Definition Exercise price of the option. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Footnote 5 + Details
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- Definition Options with exercise price greater than market price + References No definition available. + Details
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Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

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- Definition Warrants with exercise price greater than market price + References No definition available. + Details
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Namespace Prefix: | usu_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration