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Employee Benefit Plans - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Contribution on participant's elective deferrals	100.00%us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch	100.00%us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch
Discretionary contributions on behalf of participants	2.00%usbi_DefinedContributionPlanDiscretionaryContributionPercent
Contributions to the Plan	$ 0.3us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount	$ 0.3us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount
Shares held	292,989us-gaap_DefinedBenefitPlanNumberOfSharesOfEquitySecuritiesIssuedByEmployerAndRelatedPartiesIncludedInPlanAssets	321,814us-gaap_DefinedBenefitPlanNumberOfSharesOfEquitySecuritiesIssuedByEmployerAndRelatedPartiesIncludedInPlanAssets
Maximum investment in incoming contributions	20.00%us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeePercent
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Maximum participant's eligible compensation	4.00%us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent / us-gaap_RangeAxis = us-gaap_MaximumMember	4.00%us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent / us-gaap_RangeAxis = us-gaap_MaximumMember

X

- Definition

Defined contribution plan discretionary contribution percent.

+ References

No definition available.

+ Details

Name:	usbi_DefinedContributionPlanDiscretionaryContributionPercent
Namespace Prefix:	usbi_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Details

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

X

- Definition

The number of employer shares or related party shares included in plan assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (n)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

+ Details

Name:	us-gaap_DefinedBenefitPlanNumberOfSharesOfEquitySecuritiesIssuedByEmployerAndRelatedPartiesIncludedInPlanAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Amount of discretionary contributions made by an employer to a defined contribution plan.

+ References

No definition available.

+ Details

Name:	us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

+ References

No definition available.

+ Details

Name:	us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Percentage employer matches of the employee's percentage contribution matched.

+ References

No definition available.

+ Details

Name:	us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Maximum percentage of employee gross pay the employee may contribute to a defined contribution plan.

+ References

No definition available.

+ Details

Name:	us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeePercent
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: