Amount of direct write-downs of accounts receivable charged against the allowance.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 954

-SubTopic 310

-Section 50

-Paragraph 3

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=51673446&loc=SL9156395-115594

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5074-111524

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.4)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

+ References

+ Details

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

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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

- References

No definition available.

+ Details

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

- Definition

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

+ References

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

+ References

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The balance of financing receivables that were collectively evaluated for impairment.

+ References

+ Details

Name:	us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The balance of financing receivables that were individually evaluated for impairment.

+ References

+ Details

Name:	us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (g)

-URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953423-111524

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953423-111524

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.7(d))

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (b)(1)(ii)

-URI http://asc.fasb.org/extlink&oid=6379141&loc=d3e15032-111544

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 6

-Section L

-Subsection 1

+ Details

Name:	us-gaap_LoansAndLeasesReceivableAllowance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4428-111522

+ Details

Name:	us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Provision reduction in reserve for loan losses.

+ References

No definition available.

+ Details

Name:	usbi_ProvisionReductionInReserveForLoanLosses
Namespace Prefix:	usbi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=usbi_FirstUnitedSecurityBankMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=usbi_AcceptanceLoanCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=usbi_FirstUnitedSecurityBankAndAcceptanceLoanCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Loans and Allowance for Loan Losses - Schedule of Changes in Allowance for Loan Losses and Recorded Investment in Loans (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Allowance for loan losses:
Beginning balance			$ 6,168
Provision (reduction in reserve) for loan losses	$ (78)	$ (55)	(199)	$ 95
Ending balance	4,345		4,345		$ 6,168
Loan receivables:
Ending balance	251,800		251,800		274,317
Commercial and Industrial Loans [Member]
Loan receivables:
Ending balance	18,796		18,796		16,838
Consumer Loans [Member]
Loan receivables:
Ending balance	81,615		81,615		69,021
Other Loans [Member]
Loan receivables:
Ending balance	486		486		579
FUSB [Member]
Allowance for loan losses:
Beginning balance			3,486	6,272	6,272
Charge-offs			(361)		(1,941)
Recoveries			186		1,075
Provision (reduction in reserve) for loan losses			(1,370)		(1,920)
Ending balance	1,941		1,941		3,486
Ending balance individually evaluated for impairment	818		818		762
Ending balance collectively evaluated for impairment	1,123		1,123		2,724
Loan receivables:
Ending balance	159,040		159,040		191,175
Ending balance individually evaluated for impairment	6,284		6,284		10,605
Ending balance collectively evaluated for impairment	152,756		152,756		180,570
FUSB [Member] \| Commercial and Industrial Loans [Member]
Allowance for loan losses:
Beginning balance			141	592	592
Charge-offs					(289)
Recoveries			49		307
Provision (reduction in reserve) for loan losses			(55)		(469)
Ending balance	135		135		141
Ending balance individually evaluated for impairment	89		89
Ending balance collectively evaluated for impairment	46		46		141
Loan receivables:
Ending balance	18,796		18,796		16,838
Ending balance individually evaluated for impairment	453		453
Ending balance collectively evaluated for impairment	18,343		18,343		16,838
FUSB [Member] \| Commercial Real Estate [Member]
Allowance for loan losses:
Beginning balance			2,810	4,852	4,852
Charge-offs			(278)		(1,329)
Recoveries			12		587
Provision (reduction in reserve) for loan losses			(975)		(1,300)
Ending balance	1,569		1,569		2,810
Ending balance individually evaluated for impairment	729		729		762
Ending balance collectively evaluated for impairment	840		840		2,048
Loan receivables:
Ending balance	100,861		100,861		135,775
Ending balance individually evaluated for impairment	5,831		5,831		10,509
Ending balance collectively evaluated for impairment	95,030		95,030		125,266
FUSB [Member] \| Consumer Loans [Member]
Allowance for loan losses:
Beginning balance			114	180	180
Charge-offs			(16)		(147)
Recoveries			53		129
Provision (reduction in reserve) for loan losses			(114)		(48)
Ending balance	37		37		114
Ending balance collectively evaluated for impairment	37		37		114
Loan receivables:
Ending balance	6,848		6,848		7,188
Ending balance collectively evaluated for impairment	6,848		6,848		7,188
FUSB [Member] \| Residential Real Estate [Member]
Allowance for loan losses:
Beginning balance			421	635	635
Charge-offs			(67)		(176)
Recoveries			72		51
Provision (reduction in reserve) for loan losses			(241)		(89)
Ending balance	185		185		421
Ending balance collectively evaluated for impairment	185		185		421
Loan receivables:
Ending balance	32,049		32,049		30,795
Ending balance individually evaluated for impairment					96
Ending balance collectively evaluated for impairment	32,049		32,049		30,699
FUSB [Member] \| Other Loans [Member]
Allowance for loan losses:
Beginning balance				13	13
Recoveries					1
Provision (reduction in reserve) for loan losses			15		(14)
Ending balance	15		15
Ending balance collectively evaluated for impairment	15		15
Loan receivables:
Ending balance	486		486		579
Ending balance collectively evaluated for impairment	486		486		579
ALC [Member]
Allowance for loan losses:
Beginning balance			2,682	3,124	3,124
Charge-offs			(2,019)		(3,089)
Recoveries			570		801
Provision (reduction in reserve) for loan losses			1,171		1,846
Ending balance	2,404		2,404		2,682
Ending balance collectively evaluated for impairment	2,404		2,404		2,682
Loan receivables:
Ending balance	92,760		92,760		83,142
Ending balance collectively evaluated for impairment	92,760		92,760		83,142
ALC [Member] \| Consumer Loans [Member]
Allowance for loan losses:
Beginning balance			2,336	2,667	2,667
Charge-offs			(1,846)		(2,778)
Recoveries			553		772
Provision (reduction in reserve) for loan losses			1,100		1,675
Ending balance	2,143		2,143		2,336
Ending balance collectively evaluated for impairment	2,143		2,143		2,336
Loan receivables:
Ending balance	74,767		74,767		61,833
Ending balance collectively evaluated for impairment	74,767		74,767		61,833
ALC [Member] \| Residential Real Estate [Member]
Allowance for loan losses:
Beginning balance			346	457	457
Charge-offs			(173)		(311)
Recoveries			17		29
Provision (reduction in reserve) for loan losses			71		171
Ending balance	261		261		346
Ending balance collectively evaluated for impairment	261		261		346
Loan receivables:
Ending balance	17,993		17,993		21,309
Ending balance collectively evaluated for impairment	17,993		17,993		21,309
FUSB & ALC [Member]
Allowance for loan losses:
Beginning balance			6,168	9,396	9,396
Charge-offs			(2,380)		(5,030)
Recoveries			756		1,876
Provision (reduction in reserve) for loan losses			(199)		(74)
Ending balance	4,345		4,345		6,168
Ending balance individually evaluated for impairment	818		818		762
Ending balance collectively evaluated for impairment	3,527		3,527		5,406
Loan receivables:
Ending balance	251,800		251,800		274,317
Ending balance individually evaluated for impairment	6,284		6,284		10,605
Ending balance collectively evaluated for impairment	245,516		245,516		263,712
FUSB & ALC [Member] \| Commercial and Industrial Loans [Member]
Allowance for loan losses:
Beginning balance			141	592	592
Charge-offs					(289)
Recoveries			49		307
Provision (reduction in reserve) for loan losses			(55)		(469)
Ending balance	135		135		141
Ending balance individually evaluated for impairment	89		89
Ending balance collectively evaluated for impairment	46		46		141
Loan receivables:
Ending balance	18,796		18,796		16,838
Ending balance individually evaluated for impairment	453		453
Ending balance collectively evaluated for impairment	18,343		18,343		16,838
FUSB & ALC [Member] \| Commercial Real Estate [Member]
Allowance for loan losses:
Beginning balance			2,810	4,852	4,852
Charge-offs			(278)		(1,329)
Recoveries			12		587
Provision (reduction in reserve) for loan losses			(975)		(1,300)
Ending balance	1,569		1,569		2,810
Ending balance individually evaluated for impairment	729		729		762
Ending balance collectively evaluated for impairment	840		840		2,048
Loan receivables:
Ending balance	100,861		100,861		135,775
Ending balance individually evaluated for impairment	5,831		5,831		10,509
Ending balance collectively evaluated for impairment	95,030		95,030		125,266
FUSB & ALC [Member] \| Consumer Loans [Member]
Allowance for loan losses:
Beginning balance			2,450	2,847	2,847
Charge-offs			(1,862)		(2,925)
Recoveries			606		901
Provision (reduction in reserve) for loan losses			986		1,627
Ending balance	2,180		2,180		2,450
Ending balance collectively evaluated for impairment	2,180		2,180		2,450
Loan receivables:
Ending balance	81,615		81,615		69,021
Ending balance collectively evaluated for impairment	81,615		81,615		69,021
FUSB & ALC [Member] \| Residential Real Estate [Member]
Allowance for loan losses:
Beginning balance			767	1,092	1,092
Charge-offs			(240)		(487)
Recoveries			89		80
Provision (reduction in reserve) for loan losses			(170)		82
Ending balance	446		446		767
Ending balance collectively evaluated for impairment	446		446		767
Loan receivables:
Ending balance	50,042		50,042		52,104
Ending balance individually evaluated for impairment					96
Ending balance collectively evaluated for impairment	50,042		50,042		52,008
FUSB & ALC [Member] \| Other Loans [Member]
Allowance for loan losses:
Beginning balance				$ 13	13
Recoveries					1
Provision (reduction in reserve) for loan losses			15		(14)
Ending balance	15		15
Ending balance collectively evaluated for impairment	15		15
Loan receivables:
Ending balance	486		486		579
Ending balance collectively evaluated for impairment	$ 486		$ 486		$ 579