Allowance for Credit Losses - Schedule of Allowance for Loan Losses and Carrying Amount of Loans (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended	12 Months Ended
Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	$ 75,573		$ 75,529	$ 74,198	$ 74,198
Charge-offs	6,627		12,735		25,241
Recoveries	553		1,351		4,635
Provision	5,716	$ 6,201	11,070	10,880	21,937
Allowance for Loan Losses Ending balance	75,215		75,215		75,529
Allowance for Loan Losses, individually evaluated for impairment	21,769		21,769		14,946
Allowance for Loan Losses, collectively evaluated for impairment	53,446		53,446		60,583
Financing receivables	9,097,301		9,097,301		9,119,492
Financing receivables, individually evaluated for impairment	99,418		99,418		87,450
Financing receivables, collectively evaluated for impairment	8,835,810		8,835,810		8,855,703
Loans Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses	0		0		0
Financing receivables	162,073		162,073		176,339
Owner-Occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	4,406		4,041	5,653	5,653
Charge-offs	507		4,128		3,073
Recoveries	18		120		2,372
Provision	330		4,214		(911)
Allowance for Loan Losses Ending balance	4,247		4,247		4,041
Allowance for Loan Losses, individually evaluated for impairment	1,098		1,098		776
Allowance for Loan Losses, collectively evaluated for impairment	3,149		3,149		3,265
Financing receivables	962,615		962,615		1,016,364
Financing receivables, individually evaluated for impairment	13,890		13,890		12,869
Financing receivables, collectively evaluated for impairment	920,376		920,376		971,408
Owner-Occupied [Member] \| Loans Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses	0		0		0
Financing receivables	28,349		28,349		32,087
Nonowner-Occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	7,670		8,167	8,992	8,992
Charge-offs	157		327		2,097
Recoveries	20		38		268
Provision	(237)		(582)		1,004
Allowance for Loan Losses Ending balance	7,296		7,296		8,167
Allowance for Loan Losses, individually evaluated for impairment	1,347		1,347		797
Allowance for Loan Losses, collectively evaluated for impairment	5,949		5,949		7,370
Financing receivables	2,719,910		2,719,910		2,760,189
Financing receivables, individually evaluated for impairment	22,281		22,281		13,733
Financing receivables, collectively evaluated for impairment	2,643,554		2,643,554		2,692,374
Nonowner-Occupied [Member] \| Loans Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses	0		0		0
Financing receivables	54,075		54,075		54,082
Other Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	28,587		26,931	20,917	20,917
Charge-offs	3,801		4,052		4,947
Recoveries	85		196		294
Provision	3,605		5,401		10,667
Allowance for Loan Losses Ending balance	28,476		28,476		26,931
Allowance for Loan Losses, individually evaluated for impairment	11,887		11,887		7,168
Allowance for Loan Losses, collectively evaluated for impairment	16,589		16,589		19,763
Financing receivables	1,607,719		1,607,719		1,577,438
Financing receivables, individually evaluated for impairment	28,798		28,798		27,491
Financing receivables, collectively evaluated for impairment	1,554,816		1,554,816		1,523,504
Other Commercial [Member] \| Loans Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses	0		0		0
Financing receivables	24,105		24,105		26,443
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	14,557		13,835	16,694	16,694
Charge-offs	1,509		2,132		5,027
Recoveries	208		271		573
Provision	1,664		2,946		1,595
Allowance for Loan Losses Ending balance	14,920		14,920		13,835
Allowance for Loan Losses, individually evaluated for impairment	3,578		3,578		2,578
Allowance for Loan Losses, collectively evaluated for impairment	11,342		11,342		11,257
Financing receivables	2,248,037		2,248,037		2,263,354
Financing receivables, individually evaluated for impairment	16,994		16,994		16,189
Financing receivables, collectively evaluated for impairment	2,213,383		2,213,383		2,227,605
Residential Real Estate [Member] \| Loans Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses	0		0		0
Financing receivables	17,660		17,660		19,560
Construction & Land Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	16,945		19,402	18,953	18,953
Charge-offs	2		771		7,476
Recoveries	62		387		685
Provision	(30)		(2,043)		7,240
Allowance for Loan Losses Ending balance	16,975		16,975		19,402
Allowance for Loan Losses, individually evaluated for impairment	3,859		3,859		3,627
Allowance for Loan Losses, collectively evaluated for impairment	13,116		13,116		15,775
Financing receivables	1,162,742		1,162,742		1,133,251
Financing receivables, individually evaluated for impairment	17,455		17,455		17,168
Financing receivables, collectively evaluated for impairment	1,107,442		1,107,442		1,071,966
Construction & Land Development [Member] \| Loans Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses	0		0		0
Financing receivables	37,845		37,845		44,117
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	3,251		3,083	2,945	2,945
Charge-offs	651		1,325		2,621
Recoveries	160		339		443
Provision	409		1,072		2,316
Allowance for Loan Losses Ending balance	3,169		3,169		3,083
Allowance for Loan Losses, individually evaluated for impairment	0		0		0
Allowance for Loan Losses, collectively evaluated for impairment	3,169		3,169		3,083
Financing receivables	396,278		396,278		368,896
Financing receivables, individually evaluated for impairment	0		0		0
Financing receivables, collectively evaluated for impairment	396,239		396,239		368,846
Consumer [Member] \| Loans Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses	0		0		0
Financing receivables	39		39		50
Allowance for Estimated Imprecision [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	157		70	$ 44	44
Charge-offs	0		0		0
Recoveries	0		0		0
Provision	(25)		62		26
Allowance for Loan Losses Ending balance	132		132		70
Allowance for Loan Losses, individually evaluated for impairment	0		0		0
Allowance for Loan Losses, collectively evaluated for impairment	132		132		70
Financing receivables	0		0		0
Financing receivables, individually evaluated for impairment	0		0		0
Financing receivables, collectively evaluated for impairment	0		0		0
Allowance for Estimated Imprecision [Member] \| Loans Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses	0		0		0
Financing receivables	$ 0		$ 0		$ 0

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

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

- Definition

Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

+ References

+ Details

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

- Definition

A valuation allowance for financing receivables that are expected to be uncollectible.

+ References

+ Details

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

- 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

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.

+ References

No definition available.

+ Details

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

- 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

Net amount of the investment in a contractual right to receive money on demand or on fixed or determinable dates that is recognized as an asset in the creditor's statement of financial position. Examples include, but are not limited to, credit card receivables, notes receivable and receivables relating to lessor's rights to payments from leases other than operating leases that have been recorded as assets. Excludes trade accounts receivable with contractual maturity of one year or less and arose from the sale of goods or services.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.3)

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

+ Details

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

- Definition

Amount of expense related to estimated loss from loan and lease transactions.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-04.11)

-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3602-108585

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (c)(2)

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

+ Details

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

- Details

Name:	us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis=us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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