1001 - Document - Cover link:presentationLink link:definitionLink link:calculationLink 1002 - Statement - Statements of Net Assets Available for Benefits—Modified Cash Basis link:presentationLink link:definitionLink link:calculationLink 1003 - Statement - Statement of Changes in Net Assets Available for Benefits—Modified Cash Basis link:presentationLink link:definitionLink link:calculationLink 1004 - Disclosure - Significant Accounting Policies link:presentationLink link:definitionLink link:calculationLink 1005 - Disclosure - Description of the Plan link:presentationLink link:definitionLink link:calculationLink 1006 - Disclosure - Investments link:presentationLink link:definitionLink link:calculationLink 1007 - Disclosure - Fair Value Measurements link:presentationLink link:definitionLink link:calculationLink 1008 - Disclosure - Reconciliation of Financial Statements to Form 5500 link:presentationLink link:definitionLink link:calculationLink 1009 - Disclosure - Risks and Uncertainties link:presentationLink link:definitionLink link:calculationLink 1010 - Disclosure - Income Tax Status link:presentationLink link:definitionLink link:calculationLink 1011 - Disclosure - Transactions With Parties-in-Interest link:presentationLink link:definitionLink link:calculationLink 1012 - Disclosure - Commitments and Contingencies link:presentationLink link:definitionLink link:calculationLink 1013 - Disclosure - Schedule H, Line 4i – Schedule of Assets (Held at End of Year)—Modified Cash Basis link:presentationLink link:definitionLink link:calculationLink 1014 - Disclosure - Significant Accounting Policies (Policies) link:presentationLink link:definitionLink link:calculationLink 1015 - Disclosure - Fair Value Measurements (Tables) link:presentationLink link:definitionLink link:calculationLink 1016 - Disclosure - Reconciliation of Financial Statements to Form 5500 (Tables) link:presentationLink link:definitionLink link:calculationLink 1017 - Disclosure - Significant Accounting Policies - Additional Information (Details) link:presentationLink link:definitionLink link:calculationLink 1018 - Schedule - Description of the Plan - Additional Information (Details) link:presentationLink link:definitionLink link:calculationLink 1019 - Schedule - Fair Value Measurements - Summary of financial assets measured at fair value (Details) link:presentationLink link:definitionLink link:calculationLink 1020 - Disclosure - Reconciliation of Financial Statements to Form 5500 - Summary of reconciliation of net assets (Details) link:presentationLink link:definitionLink link:calculationLink 1021 - Disclosure - Reconciliation of Financial Statements to Form 5500 - Summary of reconciliation of the decrease in net assets (Details) link:presentationLink link:definitionLink link:calculationLink 1022 - Disclosure - Transactions With Parties-in-Interest - Additional Information (Detail) link:presentationLink link:definitionLink link:calculationLink 1023 - Disclosure - Schedule H, Line 4i – Schedule of Assets (Held at End of Year)—Modified Cash Basis (Detail) link:presentationLink link:definitionLink link:calculationLink 1024 - Disclosure - Schedule H, Line 4i – Schedule of Assets (Held at End of Year)—Modified Cash Basis (Detail) Alternate link:presentationLink link:definitionLink link:calculationLink Cover [Abstract] Document Type Amendment Flag Document Period End Date Document Fiscal Year Focus Document Fiscal Period Focus Entity Registrant Name Entity Central Index Key Current Fiscal Year End Date EBP, Statement of Net Asset Available for Benefit [Abstract] EBP, Statement of Net Asset Available for Benefit [Table] EBP, Statement of Net Asset Available for Benefit [Line Items] EBP, Asset [Abstract] EBP, Investment, Plan Interest in Master Trust, Fair Value Investments, at fair value EBP, Note Receivable from Participant Notes receivable from participants EBP, Net Asset Available for Benefit Net assets available for benefits Beginning of year End of year Net assets available for benefits per the financial statements Legal Entity [Axis] Entity [Domain] EBP 003 [Member] EBP, Statement of Change in Net Asset Available for Benefit [Abstract] EBP, Statement of Change in Net Asset Available for Benefit [Table] EBP, Statement of Change in Net Asset Available for Benefit [Line Items] EBP, Change in Net Asset Available for Benefit, Increase from Interest and Dividend Income on Investment [Abstract] Investment income: EBP, Change in Net Asset Available for Benefit, Increase from Interest and Dividend Income on Investment Interest and dividends EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Gain (Loss) on Investment Net appreciation in fair value of investments EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Income (Loss) on Investment Total investment gain EBP, Change in Net Asset Available for Benefit, Increase from Contribution [Abstract] Contributions: EBP, Change in Net Asset Available for Benefit, Increase from Participant Contribution, Excluding Rollover Employee contributions EBP, Change in Net Asset Available for Benefit, Increase from Employer Contribution, Cash and Noncash Employer contributions EBP, Change in Net Asset Available for Benefit, Increase from Participant Contribution, Rollover Rollover contributions EBP, Change in Net Asset Available for Benefit, Increase from Contribution Total contributions EBP, Change in Net Asset Available for Benefit, Increase Total additions EBP, Change in Net Asset Available for Benefit, Decrease [Abstract] Deductions EBP, Change in Net Asset Available for Benefit, Decrease from Payment to Participant Withdrawals and benefits paid directly to participants EBP, Change in Net Asset Available for Benefit, Decrease from Administrative Expense Administrative expenses paid by participants EBP, Change in Net Asset Available for Benefit, Decrease Total deductions EBP, Change in Net Asset Available for Benefit, Increase (Decrease) Increase in net assets available for benefits per the financial statements EBP, Accounting Policy, Accounting Standard Update, and Change in Accounting Principle [Abstract] EBP, Accounting Policy [Table] EBP, Accounting Policy [Line Items] EBP, Summary of Accounting Policy [Text Block] Significant Accounting Policies EBP, Description of Plan and Accounting Change [Abstract] EBP, Description of Plan [Table] EBP, Description of Plan [Line Items] EBP, Description of Plan [Text Block] Description of the Plan Employee Benefit Plan Investment [Abstract] Employee Benefit Plan Investment [Table] Employee Benefit Plan Investment. Employee Benefit Plan Investment [Line Items] Employee Benefit Plan Investment [Text Block] Investments Employee benefit plan investment. EBP, Investment, Fair Value and NAV [Abstract] EBP, Investment, Fair Value and NAV [Table] EBP, Investment, Fair Value and NAV [Line Items] EBP, Investment, Fair Value and NAV [Text Block] Fair Value Measurements EBP, Reconciliation of Financial Statement to Form 5500 [Abstract] EBP, Reconciliation of Financial Statement to Form 5500 [Table] EBP, Reconciliation of Financial Statement to Form 5500 [Line Items] EBP, Reconciliation of Financial Statement to Form 5500 [Text Block] Reconciliation of Financial Statements to Form 5500 EBP, Risk and Uncertainty [Abstract] EBP, Risk and Uncertainty [Table] EBP, Risk and Uncertainty [Line Items] EBP, Risk and Uncertainty [Text Block] Risks and Uncertainties EBP, Tax Status [Abstract] EBP, Tax Status [Table] EBP, Tax Status [Line Items] EBP, Tax Status [Text Block] Income Tax Status EBP, Related Party and Party-in-Interest Transactions [Abstract] EBP, Related Party and Party-in-Interest Transactions [Table] EBP, Related Party and Party-in-Interest Transactions [Line Items] EBP, Related Party and Party-in-Interest Transactions [Text Block] Transactions With Parties-in-Interest Employee Benefit Plan Commitments And Contingencies [Abstract] EBP, Contingency [Table] Employee Benefit Plan Commitments And Contingencies [Line Items] Employee Benefit Plan Commitments And Contingencies [Text Block] Commitments and Contingencies Employee Benefit Plan Commitments And Contingencies EBP, Contingency [Abstract] EBP, Schedule of Asset Held for Investment [Table] EBP, Schedule of Asset Held for Investment [Line Items] EBP, Schedule of Asset Held for Investment [Table Text Block] Schedule H, Line 4i - Schedule of Assets (Held at End of Year) - Modified Cash Basis EBP, Basis of Accounting [Policy Text Block] Accounting Method EBP, Investment [Policy Text Block] Investment Valuation and Income Recognition EBP, Note Receivable from Participant [Policy Text Block] Notes Receivable from Participants EBP, Investment, Fair Value and NAV [Table Text Block] Summary of financial assets measured at fair value EBP, Reconciliation of Financial Statement to Form 5500 [Table Text Block] Summary of reconciliation of net assets Employee Benefit Plan Reconciliation Of The Changes In Net Assets As Per Form 5500 [Text Block] Summary of reconciliation of the decrease in net assets Employee benefit plan reconciliation of the changes in net assets as per form 5500. Acquisition of Subsidiary Description Acquisition of subsidiary description Acquisition of subsidiary description. Statistical Measurement [Axis] Statistical Measurement [Domain] Maximum [Member] Minimum [Member] Employee Benefit Plan Mandatory Cash Out Limit Dollar amount that allows employers to cash out or transfer a former employee's vested retirement account balance without the former employee's consent. EBP, Participant Contribution, Pretax, Maximum Annual Compensation to Total Compensation, Percentage EBP, Employer Contribution, Participant Compensation Matched, Percentage EBP, Participant Contribution, Automatic, Deferral Rate Employee Benefit Plan Participant Advisory Services Fee Employee Benefit Plan Participant Advisory Services Fee. Employee Benefit Plan Participant Annual Trust Fee Employee benefit plan participant annual trust fee. Employee Benefit Plan Participant Record Keeping Fee The fee charged to each retirement plan participant to cover the administrative costs of maintaining account balances, processing transactions, and issuing statements. Employee Benefit Plan Participant Loan Maintenance Fee Ongoing administrative charge to cover the paperwork and tracking of a participant's borrowed funds from a retirement plan. Employee Benefit Plan Participant Loan Origination Fee One-time administrative charge to cover the paperwork and processing of a participant loan from a retirement plan. Employee Benefit Plan Participant Catch-up Contribution Year Age The age for retirement plan participants to contribute extra money for retirement beyond standard IRS limits. Percent Increment For Investment Elections Percentage increment that dictates how to divide retirement contributions among different funds. Annual Increase In General Advisory Services Fee Annual increase in the general advisory services fee to compensate a financial professional to monitor the performance of funds within a retirement plan and give personalized financial advice. Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Domain] Fair Value, Inputs, Level 1 [Member] Quoted Prices in Active Markets for Identical Assets (Level 1) Fair Value, Inputs, Level 2 [Member] Significant Other Observable Inputs (Level 2) Fair Value, Inputs, Level 3 [Member] Significant Unobservable Inputs (Level 3) Investment Type [Axis] Investments [Domain] Company Stock [Member] Company stock. Mutual Fund [Member] Investment At Nav [Member] Investment at nav. EBP, Form 5500 Caption, Net Assets Net assets available for benefits per the Form 5500 EBP, Form 5500 Caption, Participant Loans Participant loans in default EBP, Reconciliation to Form 5500, Change in Net Asset Available for Benefit, Increase (Decrease) from Deemed Distribution Net change in deemed distributions for defaulted loans EBP, Form 5500 Caption, Net Income (Loss) Net gain per the Form 5500 EBP, Related Party and Party-in-Interest [Axis] EBP, Related Party and Party-in-Interest [Domain] EBP, Other Related Party and Party-in-Interest [Member] EBP, Change in Net Asset Available for Benefit, Increase from Dividend Income on Investment EBP, Investment, Number of Shares Employee Benefit Plan Investment Fair Value Per Share Per share fair value of the Company's stock. EBP, Schedule of Asset Held for Investment [Abstract] Investment, Identifier [Axis] Investment, Issuer Name [Axis] Investment, Issuer Name [Domain] Entity Tax Identification Number EBP, Plan Number EBP, Investment, Issuer Name [Extensible Enumeration] EBP, Investment, Current Value, Type [Extensible Enumeration] EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration] EBP, Asset Held for Investment, Participant Loan, Interest Rate EBP, Asset Held for Investment, Plan Interest in Master Trust, Current Value EBP, Asset Held for Investment EBP, Participant-Directed and Nonparticipant-Directed Status [Axis] EBP, Participant-Directed and Nonparticipant-Directed Status [Domain] American Beacon Small Cap Value R6 [Member] Fiam Core Plus Commingled Pool Class I [Member] Galliard Stable Return Fund E [Member] Great Gray Trust Europacific Growth CT [Member] JP Morgan Large Cap Growth R6 [Member] MassMutual Small Cap Gr Eq CIT Fee CI CT [Member] MFS Large Cap Value CIT CL CT [Member] MFS Mid Cap Growth Fund CT [Member] MFS Mid Cap Value Fund CT [Member] NT Collective ACWI EX US IMI DC NL CT [Member] NT Collective AGG Bond NL Tier CT [Member] NT Collective Extended Equity DC NL CT [Member] NT Collective SP 500 DC NL Tier CT [Member] United Bankshares, Inc. Common Stock [Member] Vanguard Target Retirement 2020 Inv [Member] Vanguard Target Retirement 2025 Inv [Member] Vanguard Target Retirement 2030 Inv [Member] Vanguard Target Retirement 2035 Inv [Member] Vanguard Target Retirement 2040 Inv [Member] Vanguard Target Retirement 2045 Inv [Member] Vanguard Target Retirement 2050 Inv [Member] Vanguard Target Retirement 2055 Inv [Member] Vanguard Target Retirement 2060 Inv [Member] Vanguard Target Retirement 2065 Inv [Member] Vanguard Target Retirement 2070 Inv [Member] Vanguard Target Retirement Income Inv [Member] shares [Member] units [Member] EBP, Participant-Directed [Member]