Loans and Allowance for Loan Losses - Schedule of Average Net Investment Impaired Loans and Interest Income Recognized and Received on Impaired Loans (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2015	Dec. 31, 2014
Financing Receivable Impaired [Line Items]
Average Recorded Investment	$ 8,003	$ 14,743
Interest Income Recognized	176	552
Interest Income Received	429	540
Real Estate [Member] \| Construction, Land Development and Other Land Loans [Member]
Financing Receivable Impaired [Line Items]
Average Recorded Investment	1,509	2,769
Interest Income Recognized	31	46
Interest Income Received	33	46
Real Estate [Member] \| Secured by 1-4 Family Residential Properties [Member]
Financing Receivable Impaired [Line Items]
Average Recorded Investment	96	143
Interest Income Recognized		3
Interest Income Received		3
Real Estate [Member] \| Secured by Multi-family Residential Properties [Member]
Financing Receivable Impaired [Line Items]
Average Recorded Investment	2,289	3,565
Interest Income Recognized	48	178
Interest Income Received	69	170
Real Estate [Member] \| Secured by Non-farm, Non-residential Properties [Member]
Financing Receivable Impaired [Line Items]
Average Recorded Investment	3,906	8,186
Interest Income Recognized	79	324
Interest Income Received	309	320
Commercial and Industrial Loans [Member]
Financing Receivable Impaired [Line Items]
Average Recorded Investment	203	80
Interest Income Recognized	18	1
Interest Income Received	$ 18	$ 1

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

+ Details

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

- Definition

Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 15

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5212-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 17

-URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5258-111524

+ Details

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

- Definition

Amount of interest income recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of interest income recognized on a cash-basis method of accounting that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=usbi_RealEstatePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=usbi_ConstructionLandDevelopmentAndOtherLandLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=usbi_SecuredByOneToFourFamilyResidentialPropertiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=usbi_SecuredByMultiFamilyResidentialPropertiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=usbi_SecuredByNonfarmNonresidentialPropertiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: