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Fair Value of Financial Instruments - Additional Information (Detail) - USD ($) | Jun. 30, 2015 | Dec. 31, 2014
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Recurring Fair Value Measurements [Member] |  |
Fair Value Measurement [Line Items] |  |
Liabilities measured at fair value on recurring basis | $ 0 | $ 0

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- Definition Fair value of financial and nonfinancial obligations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
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Balance Type: | credit
Period Type: | instant

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- Definition Fair value measurement. + References No definition available. + Details
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Namespace Prefix: | usbi_
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Balance Type: | na
Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
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