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Loans and Allowance for Loan Losses - Additional Information (Detail) (USD $)
 3 Months Ended 12 Months Ended
Mar. 31, 2015
Segment
Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Number of portfolio segments 8usbi_NumberOfPortfolioSegments  
Related party loans and commitments $ 3,000,000us-gaap_LoansAndLeasesReceivableRelatedParties $ 3,100,000us-gaap_LoansAndLeasesReceivableRelatedParties
New loans to parties 0us-gaap_LoansAndLeasesReceivableRelatedPartiesAdditions 0us-gaap_LoansAndLeasesReceivableRelatedPartiesAdditions
Repayments of loan 30,000us-gaap_LoansAndLeasesReceivableRelatedPartiesCollections 500,000us-gaap_LoansAndLeasesReceivableRelatedPartiesCollections
Loans on which the accrual of interest has been discontinued 2,522,000us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus 4,826,000us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus
Accrued interest on loans 30,000usbi_ImpairedFinancingReceivableInterestIncomeAccrual 100,000usbi_ImpairedFinancingReceivableInterestIncomeAccrual
Interest income recorded 30,000usbi_InterestIncomeRecorded 200,000usbi_InterestIncomeRecorded
Accruing loans past due 90 days or more amounted 1,700,000us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing 1,700,000us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing
Trouble Debt restructuring Modified period term 6 months  
Period of repayment performance under the modified loan terms 6 months  
Non-accruing loans restructured and remained on nonaccrual status 1,500,000usbi_FinancingReceivableRestructuringRecordedInvestmentWithNonaccrualStatus 4,900,000usbi_FinancingReceivableRestructuringRecordedInvestmentWithNonaccrualStatus
Repayments of loans 200,000usbi_RepaymentOfLoans 0usbi_RepaymentOfLoans
Troubled debt restructuring evaluated impairment 500,000us-gaap_FinancingReceivableModificationsRecordedInvestment 500,000us-gaap_FinancingReceivableModificationsRecordedInvestment
Allowance for loans losses 10,000us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment 900,000us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment
Restructured Loans [Member]    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Troubled debt restructuring evaluated impairment 0us-gaap_FinancingReceivableModificationsRecordedInvestment
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= usbi_RestructuredLoansMember		  
Allowance for loans losses 0us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= usbi_RestructuredLoansMember		  
Minimum [Member]    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Loan amount threshold for impairment analysis $ 500,000us-gaap_LoansAndLeasesReceivableImpairedNonperformingNonaccrualOfInterest
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		  
Real Estate [Member]    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Percentage of loan portfolio 65.50%usbi_PercentageOfLoanPortfolio
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= usbi_RealEstatePortfolioSegmentMember		 68.50%usbi_PercentageOfLoanPortfolio
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= usbi_RealEstatePortfolioSegmentMember