Document And Entity Information
Credit Card, Merchant Discount [Member]
Marketable Securities, Policy [Policy Text Block]
Statistical Measurement [Axis]
wabc_LoanCommitmentsNotUnconditionallyCancellable
Loan Commitments, Not Unconditionally Cancellable
The portion of loan commitments that are not unconditionally cancellable.
Note To Financial Statement Details Textual
Significant Accounting Policies
Provision for income taxes
Term Loan Originated Prior [Member]
Represents term loans originated prior.
Note 3 - Debt Securities Available for Sale and Held to Maturity
ecd_NonRule10b51ArrTrmntdFlag
Non-Rule 10b5-1 Arrangement Terminated [Flag]
Note 4 - Loans, Allowance for Credit Losses and Other Real Estate Owned
Financial Service, Other [Member]
ecd_NonRule10b51ArrAdoptedFlag
Non-Rule 10b5-1 Arrangement Adopted [Flag]
Note 6 - Other Assets and Other Liabilities
Debit Card [Member]
Trading Arrangements, by Individual [Table]
Note 7 - Goodwill and Identifiable Intangible Assets
Deposit Account [Member]
Material Terms of Trading Arrangement [Text Block]
Note 8 - Deposits and Borrowed Funds
Note 9 - Fair Value Measurements
Financial Instrument [Axis]
Note 11 - Earnings Per Common Share
Investment in Debt and Equity Securities and Other Trading Assets [Text Block]
us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss
Held to Maturity, Gross Unrealized Losses
Note 3 - Debt Securities Available for Sale and Held to Maturity - Schedule of Estimated Fair Value of Investment Securities Portfolio (Details)
us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain
Held to Maturity, Gross Unrealized Gains
us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Debt securities available for sale, gross unrealized losses
Minimum [Member]
Note 3 - Debt Securities Available for Sale and Held to Maturity - Schedule of Estimated Market Value of Securities by Contractual Maturity (Details)
us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
Debt securities available for sale, gross unrealized gains
Statistical Measurement [Domain]
Note 3 - Debt Securities Available for Sale and Held to Maturity - Gross Unrealized Losses, Investment Securities Portfolio (Details)
wabc_ConcentrationRiskAggregateLoansAmount
Concentration Risk, Aggregate Loans Amount
The amount of aggregate loans.
us-gaap_SharePrice
Share Price
Note 3 - Debt Securities Available for Sale and Held to Maturity - Allowance for Credit Losses (Details)
Note 3 - Debt Securities Available for Sale and Held to Maturity - Credit Quality (Details)
Note 3 - Debt Securities Available for Sale and Held to Maturity - Interest Income From Investment Securities (Details)
Note 4 - Loans, Allowance for Credit Losses and Other Real Estate Owned - Loans Receivable at Carrying Amount (Details)
Note 4 - Loans, Allowance for Credit Losses and Other Real Estate Owned - Allowance for Loan Losses (Details)
Note 4 - Loans, Allowance for Credit Losses and Other Real Estate Owned - Credit Risk Profile by Internally Assigned Grade (Details)
Note 4 - Loans, Allowance for Credit Losses and Other Real Estate Owned - Loans by Delinquency and Nonaccrual Status (Details)
Note 4 - Loans, Allowance for Credit Losses and Other Real Estate Owned - Risk Category of Loans by Class (Details)
Note 6 - Other Assets and Other Liabilities - Other Assets (Details)
Note 6 - Other Assets and Other Liabilities - Amounts Recognized in Net Income (Details)
Debt Securities, Available-for-Sale [Table]
Note 6 - Other Assets and Other Liabilities - Summary of Other Liabilities (Details)
Note 6 - Other Assets and Other Liabilities - Summarizes of Operating Lease Liabilities (Details)
Note 7 - Goodwill and Identifiable Intangible Assets - Carrying Values of Goodwill (Details)
Note 8 - Deposits and Borrowed Funds - Deposits Detail (Details)
Note 8 - Deposits and Borrowed Funds - Short-term Borrowed Funds (Details)
Note 9 - Fair Value Measurements - Assets Measured at Fair Value on a Recurring Basis (Details)
Collateralized Debt Obligations [Member]
Collateralized Loan Obligations [Member]
Note 9 - Fair Value Measurements - Assets Measured at Fair Value on a Nonrecurring Basis (Details)
Salaries and related benefits
Note 9 - Fair Value Measurements - Fair Value Estimates for Financial Instruments, Excluding Financial Instruments on a Recurring Basis (Details)
us-gaap_DividendsCommonStockCash
Dividends
Note 11 - Earnings Per Common Share - Earnings Per Common Share and Diluted Earnings Per Common Share (Details)
Notes To Financial Statements
Notes To Financial Statements [Abstract]
us-gaap_IncreaseDecreaseInIncomeTaxesReceivable
Income taxes payable
Financial Instruments [Domain]
Common Stock, Dividends, Per Share, Declared (in dollars per share)
Asset Pledged as Collateral [Member]
us-gaap_IncreaseDecreaseInAccruedInterestReceivableNet
Interest income receivable
Interest expense payable
us-gaap_SharesOutstanding
Balance (in shares)
Balance (in shares)
us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsNumberOfPositions
Positions
us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerNumberOfPositions
Positions
Segment Reporting [Text Block]
us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger
Fair Value
us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months
Fair Value
Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity [Abstract]
us-gaap_Liabilities
Total Liabilities
Liabilities:
Equity securities
Amount of operating dividend and interest income, including amortization and accretion of premiums and discounts on equity securities.
us-gaap_LiabilitiesAndStockholdersEquity
Total Liabilities and Shareholders' Equity
Pledged Status [Domain]
Segment Reporting [Table]
Pledged Status [Axis]
Unlikely to be Collected Financing Receivable [Member]
Lessee, Lease, Description [Table]
wabc_DebtSecuritiesGrossUnrecognizedGains
Total, gross unrealized gains
Represents the amount of gross unrecognized gains of debt securities, available-for-sale and held-to-maturity.
Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Increase (Decrease) in Operating Capital [Abstract]
Total Term Loans [Member]
Related to total term loans.
wabc_DebtSecuritiesGrossUnrecognizedLosses
Total, gross unrealized losses
Represents the amount of gross unrecognized losses of debt securities, available-for-sale and held-to-maturity.
Portion at Fair Value Measurement [Member]
Reported Value Measurement [Member]
Fair Value, by Balance Sheet Grouping [Table]
us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect
Net Change in Cash and Due from Banks
us-gaap_CashAndCashEquivalentsFairValueDisclosure
Cash and due from banks
Estimate of Fair Value Measurement [Member]
Dividends paid (in dollars per share)
Other Assets and Liabilities Disclosure [Text Block]
Complete disclosure for other assets and liabilities.
AAA/AA/A [Member]
Related to a credit rating.
New Accounting Pronouncements, Policy [Policy Text Block]
us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations
Cash and Due from Banks at Beginning of Period
Cash and Due from Banks at End of Period
US Government Agencies Debt Securities [Member]
Term Loans Originated Three Years Prior [Member]
Related to term loans.
Antidilutive Securities, Name [Domain]
Financing Receivable, Loans by Risk Category [Table Text Block]
Tabular disclosure for loans by risk category classified as financing receivable.
Statement [Table]
Term Loans Originated Four Years Prior [Member]
Related to term loans.
Cash paid for amounts included in operating lease liabilities
Revolving Loans Amortized Cost Basis [Member]
Related to revolving loans amortized cost basis.
us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss
Losses
us-gaap_LoansReceivableFairValueDisclosure
Loans
Right-of-use assets acquired in exchange for operating lease liabilities
us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition
Fair Value
us-gaap_InvestmentsFairValueDisclosure
Total equity securities
Total investment securities
us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Line of Credit Facility, Maximum Borrowing Capacity
Line of Credit Facility, Lender [Domain]
us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions
Positions
Lender Name [Axis]
Financing Receivable, Past Due [Table Text Block]
us-gaap_SecuritiesLoanedOrSoldUnderAgreementsToRepurchaseFairValueDisclosure
Securities sold under repurchase agreements
Stock awarded to employees (in shares)
Financing Receivable Credit Quality Indicators [Table Text Block]
Product and Service [Domain]
Product and Service [Axis]
us-gaap_IncreaseDecreaseInEquitySecuritiesFvNi
Equity securities held for trading
wabc_FinancingReceivableNonaccrualNumberOfLoans
Financing Receivable, Nonaccrual, Number of Loans
Number of loans on nonaccrual.
us-gaap_EquitySecuritiesFvNiUnrealizedGainLoss
Equity Securities, FV-NI, Unrealized Gain (Loss)
Thereafter
us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive
us-gaap_LoansReceivableHeldForSaleAmount
Financing Receivable, Held-for-Sale
us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue
Total minimum lease payments
Term Loans Originated Current Year [Member]
Represents term loans originated current year.
us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent
Operating Lease, Weighted Average Discount Rate, Percent
Asset Class [Axis]
Interest and Loan Fee Income:
2027
us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths
wabc_FinancingReceivableExcludingAccruedInterestNonaccrualAllowance
Financing Receivable, Excluding Accrued Interest, Nonaccrual, Allowance
Amount of allowance, excluding accrued interest, of financing receivable on nonaccrual status. Excludes net investment in lease.
The remainder of 2026
us-gaap_LesseeOperatingLeaseLiabilityPaymentsRemainderOfFiscalYear
us-gaap_LoansAndLeasesReceivableImpairedCommitmentToLend
Financing Receivable, Modified, Commitment to Lend
Lessee, Operating Lease, Liability, to be Paid, Maturity [Table Text Block]
Assets:
2029
us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree
Measurement Frequency [Axis]
2028
us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo
Commitments and Contingencies Disclosure [Text Block]
Statement [Line Items]
2030
us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFour
Fair Value Hierarchy and NAV [Axis]
Common Stock, Shares, Issued (in shares)
Common Stock, Shares, Outstanding (in shares)
Common Stock, Shares Authorized (in shares)
Common stock and additional paid-in-capital Common stock (no par value), authorized: 150,000 shares issued and outstanding: 23,002 at June 30, 2026 and 24,623 at December 31, 2025
us-gaap_IncomeLossFromAffordableHousingProjectsEquityMethodInvestments
Limited partnership operating losses
us-gaap_MortgageLoansInProcessOfForeclosureAmount
Mortgage Loans in Process of Foreclosure, Amount
us-gaap_PolicyTextBlockAbstract
Accounting Policies
Tax credits recognized in provision for income taxes
us-gaap_DisclosureTextBlockAbstract
Notes to Financial Statements
us-gaap_TableTextBlock
Notes Tables
wabc_PaymentsForExciseTaxOnShareRepurchases
Excise tax on net common stock repurchases
Amount of cash outflow for excise tax on share repurchases.
us-gaap_ComprehensiveIncomeNetOfTax
Total comprehensive income
Proceeds from bank owned life insurance policies
us-gaap_ProceedsFromLifeInsurancePolicies
Schedule of Loans Receivable [Table Text Block]
Tabular disclosure of the various types of loans receivable at gross carrying value.
Concentration Risk [Table]
us-gaap_ShortTermBorrowings
Total short-term borrowed funds
Concentration Risk Type [Axis]
Concentration Risk Disclosure [Text Block]
Significant Accounting Policies [Text Block]
Proceeds from maturity/calls of debt securities available for sale
Proceeds from maturity/calls of debt securities held to maturity
us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount
Less: discount
Operating lease liability
Operating Lease, Liability
us-gaap_DepositsFairValueDisclosure
Deposits
Fair Value, Assets Measured on Recurring Basis [Table Text Block]
Concentration Risk Type [Domain]
Contingent Commitment, Remainder of Fiscal Year [Member]
Represents information pertaining to the contingent commitment for the remainder of the fiscal year.
Financial Standby Letter of Credit [Member]
Offsetting Assets [Table]
Other comprehensive income:
wabc_HeldtomaturitySecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1
Held to Maturity securities, total, number of investment positions
Disclosure regarding factors used to determine that the impairment of securities categorized as held-to-maturity where cost exceeds fair value is not an other than temporary impairment (OTTI). This item contains disclosure of the number of investment positions in the held-to-maturity investments determined to be temporarily impaired.
Statement of Stockholders' Equity [Abstract]
Statement of Comprehensive Income [Abstract]
Loss Contingency Nature [Axis]
Equity securities held for trading at fair value
us-gaap_EquitySecuritiesFvNiCurrentAndNoncurrent
Equity Securities, FV-NI
Statement of Cash Flows [Abstract]
Financing Receivable Portfolio Segment [Axis]
Shareholders' Equity:
Equity Components [Axis]
Unfunded Loan Commitment [Member]
Financing Receivable Portfolio Segment [Domain]
Exercise of stock options
us-gaap_ProceedsFromStockOptionsExercised
Equity Component [Domain]
Fair Value Measurements, Nonrecurring [Table Text Block]
Offsetting Liabilities [Table]
Fair Value, Inputs, Level 2 [Member]
Fair Value, Inputs, Level 3 [Member]
AOCI Attributable to Parent [Member]
Fair Value, Inputs, Level 1 [Member]
Retained Earnings [Member]
Corporate Debt Securities [Member]
Loss Contingency, Nature [Domain]
Financial Instrument Performance Status [Domain]
Premises and equipment, net
Financial Asset, Aging [Axis]
Financial Instrument Performance Status [Axis]
Prepaid assets
us-gaap_PrepaidExpenseCurrentAndNoncurrent
us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss
Loans
Financing Receivable, Current, Allowance for Credit Loss [Table Text Block]
Financial Asset, Aging [Domain]
Reversal of Provision for Credit Losses
us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestBeforeAllowanceForCreditLoss
Held to Maturity, Amortized Cost
Debt securities held to maturity, amortized cost
Financial Asset, 30 to 59 Days Past Due [Member]
wabc_FinancingReceivableTermLoan
Total Term Loans
Amortized cost of financing receivable that is a term loan.
us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestBeforeAllowanceForCreditLoss
Debt securities available for sale, amortized cost
Debt securities available for sale, amortized cost
Stock awarded to employees
Intangible Asset and Goodwill [Text Block]
Debt Securities, Held-to-Maturity, Allowance for Credit Loss, Excluding Accrued Interest
Debt Securities, Held-to-Maturity, Allowance for Credit Loss, Excluding Accrued Interest
Beginning balance
Total ending balance
us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest
Allowance for credit losses on loans
Balance at beginning of period
Total allowance for credit losses
Financial Asset, 60 to 89 Days Past Due [Member]
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Deferred Compensation, Share-Based Payments [Member]
Total, fair value
wabc_DebtSecuritiesAvailableforsaleAndHeldtomaturityBeforeAllowanceForCreditLoss
Debt Securities, Available-for-Sale and Held-to-Maturity, Before Allowance for Credit Loss
Amount, before allowance for credit loss, of investment in debt security measured at amortized cost (held-to-maturity) and investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).
us-gaap_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYear
Originated four years before
us-gaap_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYear
Originated prior
us-gaap_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYear
Originated two years before
us-gaap_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYear
Originated three years before
us-gaap_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYear
Originated current year
Fair Value Disclosures [Text Block]
us-gaap_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYear
Originated one years before
Fair Value, by Balance Sheet Grouping [Table Text Block]
Share-Based Payment Arrangement, Option [Member]
Supplemental disclosure of cash flow activities:
us-gaap_FinancingReceivableExcludingAccruedInterestRevolving
Financing Receivable Revolving
us-gaap_LettersOfCreditOutstandingAmount
Letters of Credit Outstanding, Amount
Customer Concentration Risk [Member]
us-gaap_PaymentsToAcquireHeldToMaturitySecurities
Purchases of debt securities held to maturity
Other Commitments [Table]
Accumulated other comprehensive loss
us-gaap_CommonStockNoParValue
Common Stock, No Par Value (in dollars per share)
Corresponding Banks [Member]
Represents corresponding banks.
Federal Reserve [Member]
Represents federal reserve.
Other Commitments [Axis]
Other Commitments [Domain]
Public Deposits and Short-term Borrowed Funds [Member]
Represents public deposits and short-term borrowed funds.
wabc_QualifiedAffordableHousingProjectInvestmentCommitment
Qualified Affordable Housing Project Investment, Commitment
Amount of commitment and contingent commitment, including amount of delayed equity contribution, for investment that generates income tax credit and other income tax benefit under tax credit program elected.
Outsourced data processing services
wabc_DebSecuritiesHeldtomaturityExcludingAccruedInterestFairValue
Held to Maturity, Fair Value
Deb Securities, Held-to-maturity, Excluding Accrued Interest, Fair Value
Fair value of investment in debt security measured at amortized cost (held-to-maturity), excluding accrued interest.
Federal Reserve Bank stock
us-gaap_FederalReserveBankStock
Equity Based [Member]
Related to equity based.
Segment Reporting, Policy [Policy Text Block]
wabc_ShorttermLineOfCredit
Short-term Line of Credit
The amount of short-term line of credit outstanding.
us-gaap_PaymentsToAcquirePropertyPlantAndEquipment
Purchases of premises and equipment
Term Loans Originated One Year Prior [Member]
Represents term loans originated one year prior.
us-gaap_StockRepurchasedAndRetiredDuringPeriodValue
Retirement of common stock
ATM Processing Fees [Member]
Information pertaining to ATM processing fees.
us-gaap_NoninterestExpense
Total Noninterest Expense
Noninterest Expense:
Schedule of Other Assets [Table Text Block]
Exercise of stock options
Financial Asset, Not Past Due [Member]
Restricted stock activity
wabc_DebtSecuritiesAvailableforsaleAndHeldtomaturityAmortizedCost
Total, amortized cost
Amount of investment in debt security measured at amortized cost (held-to-maturity) and amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), before allowance for credit losses.
Debt Securities, Held-to-Maturity, Credit Quality Indicator [Table Text Block]
Goodwill [Table]
us-gaap_OffBalanceSheetCreditLossLiability
Off-Balance-Sheet, Credit Loss, Liability
Credit Loss, Financial Instrument [Policy Text Block]
Exercise of stock options (in shares)
Restricted stock activity (in shares)
us-gaap_StockRepurchasedAndRetiredDuringPeriodShares
Retirement of common stock (in shares)
wabc_FinancingReceivableBeforeAllowanceForCreditLossAndRevolvingLoansWriteoff
Financing Receivable, before Allowance for Credit Loss and Revolving Loans, Writeoff
The amount of write off for financing receivable before allowance for credit loss and revolving loans.
wabc_DebtSecuritiesHeldtomaturityContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss1
Held to Maturity securities, less than 12 months, unrealized loss
Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in continuous loss position for less than 12 months.
wabc_DebtSecuritiesHeldtomaturityContinuousUnrealizedLossPositionLessThan12MonthsFairValueWithoutAllowanceForCreditLoss
Held to Maturity securities, less than 12 months, fair value
Fair value of investment in debt security measured at amortized cost (held-to-maturity), in continuous unrealized loss position without allowance for credit loss for less than 12 months.
wabc_DebtSecuritiesHeldtomaturityContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss1
Held to Maturity securities, 12 months or longer, unrealized loss
Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in continuous loss position for 12 months or longer.
wabc_DebtSecuritiesHeldtomaturityContinuousUnrealizedLossPosition12MonthsOrLongerFairValue1
Held to Maturity securities, 12 months or longer, fair value
Fair value of investment in debt security measured at amortized cost (held-to-maturity), in continuous unrealized loss position for 12 months or longer.
Common Stock Including Additional Paid in Capital [Member]
us-gaap_GoodwillAndIntangibleAssetImpairment
Intangible Asset, Including Goodwill, Impairment Loss
Operating Activities:
Stock option compensation expense
Investing Activities:
us-gaap_NetCashProvidedByUsedInOperatingActivities
Net Cash Provided by Operating Activities
Financing Activities:
wabc_DebtSecuritiesHeldtomaturityUnrealizedLossPositionAccumulatedLoss
Held to Maturity securities, total, unrealized loss
Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in unrealized loss position.
us-gaap_NetCashProvidedByUsedInInvestingActivities
Net Cash (Used in) Provided by Investing Activities
wabc_DebtSecuritiesHeldtomaturityUnrealizedLossPositionFairValue1
Held to Maturity securities, total, fair value
Fair value of investment in debt security measured at amortized cost (held-to-maturity), in unrealized loss position.
us-gaap_NetCashProvidedByUsedInFinancingActivities
Net Cash Used in Financing Activities
Schedule of Unrealized Loss on Investments 1 [Table Text Block]
For all investments in an unrealized loss position, including those for which other-than-temporary impairments have not been recognized in earnings (including investments for which a portion of an other-than-temporary impairment has been recognized in other comprehensive income), a tabular disclosure of the aggregate related fair value of investments with unrealized losses and the aggregate amount of unrealized losses (that is, the amount by which amortized cost basis exceeds fair value).
Net change in short-term borrowings
us-gaap_PaymentsToAcquireAvailableForSaleSecuritiesDebt
Purchases of debt securities available for sale
wabc_OtherLiabilitiesExcludingOperatingLeaseLiability
Other liabilities
Amount of liabilities classified as other, excluding operating lease liability.
us-gaap_AssetsFairValueDisclosure
Fair Value
Financing Receivable [Policy Text Block]
Loans, Notes, Trade and Other Receivables Disclosure [Text Block]
Debt Securities, Held-to-Maturity, Allowance for Credit Loss [Table Text Block]
Net change in deposits
Accounting Policies [Abstract]
US States and Political Subdivisions Debt Securities [Member]
us-gaap_FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLoss
Loans, net of allowance for credit losses on loans
us-gaap_PaymentsForProceedsFromLoansAndLeases
Net repayments of loans
Income Statement [Abstract]
Debt securities available for sale
us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest
Debt securities available for sale
Debt securities available for sale
Debt securities held to maturity, net of allowance for credit losses of $1 at June 30, 2026 and December 31, 2025 (Fair value of $790,440 at June 30, 2026 and $812,580 at December 31, 2025)
Other assets
us-gaap_OtherAssetsMiscellaneous
Amortization of deferred loan cost
Net income (numerator)
Net income
Net Income
us-gaap_InterestIncomeExpenseNet
Net Interest and Loan Fee Income
wabc_DeferredCompensation
Deferred compensation
Increase in equity due to deferred compensation.
Courier service
Amount of contract courier expense.
Accounting Standards Update and Change in Accounting Principle [Table]
wabc_SecuredAndUnsecuredLoanLimitPercentageCaliforniaFinancialCode
Secured and Unsecured Loan Limit Percentage, California Financial Code
The loan limit percentage of secured and unsecured loans to sum of shareholders' equity, allowance for loan losses, capital notes, and debentures of the bank.
Noninterest-bearing deposits
Noninterest-bearing
wabc_UnsecuredLoanLimitPercentageOfShareholdersEquityCaliforniaFinancialCode
Unsecured Loan Limit, Percentage of Shareholders' Equity, California Financial Code
The percentage limit of unsecured loans to the sum of shareholders' equity under the California Financial Code.
Net deferred tax asset
us-gaap_DeferredTaxAssetsNet
wabc_ConcentrationRiskAggregateSecuritiesAmount
Concentration Risk, Aggregate Securities Amount
The amount of aggregate securities per customer.
wabc_ConcentrationRiskIssuerRelationships
Concentration Risk, Issuer Relationships
The number of issuer relationships related to corporate investment securities.
wabc_LoanToValueRatioRequirement
Loan To Value Ratio Requirement
The loan to value ratio requirement of the lending institution.
wabc_LoanCommitmentsRelatedToRealEstateLoans
Loan Commitments Related to Real Estate Loans
Reflects the unfunded portion of contractual agreements to lend funds to borrowers and the total amount of the contingent loans obligations related to real estate loans as of the reporting date.
Commercial Real Estate Loans [Member]
Represents commercial real estate loans.
Aggregate Loans [Member]
Represents borrow relationships aggregate loans.
Residential Real Estate Loans [Member]
Represents residential real estate loans.
Limited partnership investments
wabc_LIHTCInvestments
LIHTC Investments
Gross investment in Low Income Housing Tax Credit limited parterships.
Occupancy and equipment
Contingent Commitment, Year 2 [Member]
Amount of contingent commitments to qualified affordable housing project investments expected to be paid in year 2.
Other noninterest expense
Contingent Commitment, Year 1 [Member]
Amount of contingent commitments to qualified affordable housing project investments expected to be paid in year 1.
Schedule of Amounts Recognized in Net Income [Table Text Block]
Tabular disclosure of the amounts of limited partnership investments that are recognized in net income.
Bank owned life insurance gains
Bank owned life insurance gains
Deposits and Borrowed Funds [Text Block]
The full disclosure for deposits and borrowed funds.
us-gaap_NoninterestIncome
Total Noninterest Income
Noninterest Income:
wabc_DemandDepositOverdrafts
Demand Deposit Overdrafts
Amounts honored in excess of customers account balances, recorded by the bank as a loan.
Measurement Basis [Axis]
Time deposits $100 thousand through $250 thousand
The aggregate amount of domestic and foreign time deposit liabilities (including certificates of deposits, individual retirement accounts and open accounts) in denominations of $100,000 through $250,000.
Time deposits more than $250 thousand
The aggregate amount of domestic and foreign time deposit liabilities (including certificates of deposits, individual retirement accounts and open accounts) in denominations of more than $250,000.
Term Loans Originated Two Years Prior [Member]
Related to term loans.
Other noninterest income
wabc_UnfundedLoanCommitments
Unfunded Loan Commitments
Reflects the unfunded portion of contractual agreements to lend funds to borrowers.
Fair Value Hierarchy and NAV [Domain]
Interest Income from Investments [Table Text Block]
Tabular disclosure of interest income from investments, identified as taxable or non-taxable.
Measurement Frequency [Domain]
Statement of Financial Position [Abstract]
us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestCreditLossExpenseReversal
Provision
Asset Sold under Agreement to Repurchase [Table]
Deposit Liability [Table]
Provision (reversal)
us-gaap_FinancingReceivableExcludingAccruedInterestCreditLossExpenseReversal
Income tax payments for the period
Commercial Standby Letters of Credit [Member]
An irrevocable undertaking (typically by a financial institution) to guarantee payment of a specified financial obligation.
us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestAllowanceForCreditLossRecovery
Recoveries
us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossRecovery
Recoveries
us-gaap_OtherAssets
Other assets
Total other assets
us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff
Loans, Writeoff
Chargeoffs
us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestAllowanceForCreditLossWriteoff
Chargeoffs
NR [Member]
Related to NR.
Professional fees
Fair Value, Nonrecurring [Member]
Fair Value, Recurring [Member]
us-gaap_PaymentsForRepurchaseOfCommonStock
Retirement of common stock
us-gaap_IncreaseDecreaseInOtherOperatingAssets
Other assets
us-gaap_IncreaseDecreaseInDeferredIncomeTaxes
Deferred income taxes
dei_DocumentType
Document Type
Document Information [Line Items]
Document Quarterly Report
us-gaap_LesseeOperatingLeaseTermOfContract
Lessee, Operating Lease, Term of Contract
us-gaap_LesseeOperatingLeaseRenewalTerm
Lessee, Operating Lease, Renewal Term (Year)
us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1
Operating Lease, Weighted Average Remaining Lease Term (Year)
Document Information [Table]
wabc_HeldtomaturitySecuritiesLessThan12MonthsNumberOfPositions
Held to Maturity securities, less than 12 months, number of investment positions
Number of investment positions in held-to-maturity investments in a continuous unrealized loss position for less than one year or normal operating cycle, if longer, for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement.
us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount
Antidilutive Securities [Axis]
us-gaap_DebtSecuritiesHeldToMaturityAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityAllocatedAndSingleMaturityDateRollingAfterOneThroughFiveYears
Investment securities held to maturity, amortized cost, over 1 to 5 years
Add common stock equivalents for options (in shares)
Entity Interactive Data Current
us-gaap_DebtSecuritiesHeldToMaturityAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityAllocatedAndSingleMaturityDateRollingAfter5Through10Years
Investment securities held to maturity, amortized cost, over 5 to 10 years
Bank owned life insurance cash surrender value
us-gaap_BankOwnedLifeInsurance
Document Transition Report
Average Diluted Common Shares Outstanding (in shares)
us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding
Weighted average number of common shares outstanding - diluted (denominator) (in shares)
us-gaap_DebtSecuritiesHeldToMaturityAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityAllocatedAndSingleMaturityDateRollingWithinOneYear
Investment securities held to maturity, amortized cost, 1 year or less
us-gaap_DebtSecuritiesHeldToMaturityAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityAllocatedAndSingleMaturityDate
Investment securities held to maturity, amortized cost, subtotal
wabc_HeldtomaturitySecurities12MonthsOrLongerNumberOfPositions
Held to Maturity securities, 12 months or longer, number of investment positions
Number of investment positions in held-to-maturity investments that have been in a continuous unrealized loss position for greater than or equal to a year for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement.
us-gaap_DebtSecuritiesHeldToMaturityAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityWithoutSingleMaturityDate
Debt securities held to maturity, amortized cost, without single date maturity
Per Common Share Data:
us-gaap_AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasis
Investment securities available for sale, amortized cost, subtotal
us-gaap_AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDate
Investment securities available for sale, fair value, subtotal
Average Common Shares Outstanding (in shares)
Weighted average number of common shares outstanding - basic (denominator) (in shares)
us-gaap_HeldToMaturitySecuritiesDebtMaturitiesSingleMaturityDateFairValue
Investment securities held to maturity, fair value, subtotal
Basic earnings (in dollars per share)
Basic earnings per common share (in dollars per share)
Contingent Commitment, Year 4 [Member]
Amount of contingent commitments to qualified affordable housing project investments expected to be paid in year 4.
Earnings Per Share, Basic, by Common Class, Including Two-Class Method [Table]
us-gaap_FinancingReceivableExcludingAccruedInterestNonaccrual
Nonaccrual
us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestNonaccrual
Debt Securities, Held-to-Maturity, Excluding Accrued Interest, Nonaccrual
Equity Securities without Readily Determinable Fair Value [Policy Text Block]
Transaction
Time deposits less than $100 thousand
us-gaap_Deposits
Total deposits
Other investments
us-gaap_OtherInvestmentsAndSecuritiesAtCost
Depreciation and amortization/accretion
Document Fiscal Period Focus
Stock based compensation
Pledging Purpose [Axis]
Document Fiscal Year Focus
Pledging Purpose [Domain]
Savings
Amendment Flag
Common Stock [Member]
Goodwill
Goodwill
Other liabilities
us-gaap_IncreaseDecreaseInOtherOperatingLiabilities
Debt securities held to maturity
wabc_DebtSecuritiesHeldtomaturityFairValueDisclosure
This item represents the total of all debt securities grouped by maturity dates, at fair value, which are categorized as held-to-maturity.
Document Period End Date
Construction Portfolio Segment [Member]
Portfolio segment of the company's total financing receivables related to construction.
Residential Portfolio Segment [Member]
Legal Entity [Axis]
us-gaap_InterestAndDividendIncomeOperating
Total Interest and Loan Fee Income
Contingent Commitment, Thereafter [Member]
Relating a contingent commitments after the last reported year.
Consumer Portfolio Segment [Member]
us-gaap_OperatingLeaseCost
Operating Lease, Cost
Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Loss [Table]
Commercial Portfolio Segment [Member]
Interest-bearing deposits
dei_EntityFileNumber
Entity File Number
Entity Tax Identification Number
Supplemental Cash Flow Disclosures:
us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
Losses
us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
Losses
us-gaap_FinancingReceivableAllowanceForCreditLossesPeriodIncreaseDecrease
Financing Receivable, Allowance for Credit Loss, Period Increase (Decrease)
Entity [Domain]
Entity Central Index Key
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Loan Category [Domain]
dei_EntityRegistrantName
Entity Registrant Name
us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueAmount
Total equity securities not held for trading at cost
Doubtful [Member]
Entity Current Reporting Status
Substandard [Member]
Contingent Commitment, Year 3 [Member]
Amount of contingent commitments to qualified affordable housing project investments expected to be paid in year 3.
Entity Incorporation, State or Country Code
Pass [Member]
Current Fiscal Year End Date
us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax
Changes in net unrealized losses on debt securities available for sale, net of tax
Debt Securities, Available-for-sale and Held-to-maturity [Table Text Block]
Tabular disclosure of information about investment in debt security measured at amortized cost (held-to-maturity) or at fair value with change in fair value recognized in other comprehensive income (available-for-sale).
Entity Filer Category
Entity Shell Company
Entity Emerging Growth Company
us-gaap_OtherComprehensiveIncomeLossNetOfTax
Other comprehensive loss
Nonperforming Financial Instruments [Member]
Entity Small Business
us-gaap_InterestIncomeDebtSecuritiesAvailableForSaleOperating
Debt securities available for sale
Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]
Interest Expense:
Deposits
dei_EntityAddressStateOrProvince
Entity Address, State or Province
dei_EntityAddressCityOrTown
Entity Address, City or Town
Retained earnings
us-gaap_InterestExpenseOperating
Total Interest Expense
dei_EntityAddressAddressLine1
Entity Address, Address Line One
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Loan Category [Axis]
us-gaap_InterestExpenseTimeDeposits100000OrMore
Interest Expense, Time Deposits, $100,000 or More
Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block]
dei_CityAreaCode
City Area Code
us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost
Investment securities available for sale, amortized cost, over 1 to 5 years
us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost
Investment securities available for sale, amortized cost, over 5 to 10 years
dei_LocalPhoneNumber
Local Phone Number
us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost
Investment securities available for sale, amortized cost, 1 year or less
dei_EntityAddressPostalZipCode
Entity Address, Postal Zip Code
us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments
Income Before Income Taxes
us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue
Debt securities available for sale, without single date maturity
Title of 12(b) Security
Security Exchange Name
us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue
Investment securities available for sale, fair value, over 5 to 10 years
Trading Symbol
us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue
Investment securities available for sale, fair value, 1 year or less
us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue
Investment securities available for sale, fair value, over 1 to 5 years
us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateAmortizedCost
Debt securities available for sale, amortized cost, without single date maturity
Class of Stock [Axis]
Class of Financing Receivable [Axis]
us-gaap_InterestExpenseSecuritiesSoldUnderAgreementsToRepurchase
Securities sold under repurchase agreements
Class of Financing Receivable [Domain]
Entity Common Stock, Shares Outstanding (in shares)
Earnings Per Share [Text Block]
us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax
Deferred tax benefit (expense)
Financing Receivable, Credit Quality Indicator [Table]
Changes in net unrealized losses on debt securities available for sale
Internal Credit Assessment [Axis]
External Credit Rating by Grouping [Axis]
us-gaap_GuaranteeObligationsCurrentCarryingValue
Guarantor Obligations, Current Carrying Value
Debt securities held to maturity, fair value
us-gaap_HeldToMaturitySecuritiesFairValue
us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss
Net Interest and Fee Income After Reversal of Provision for Credit Losses
Interest-bearing cash
Investments Classified by Contractual Maturity Date [Table Text Block]
Debt securities held to maturity
us-gaap_InterestAndDividendIncomeSecuritiesHeldToMaturity
Off-Balance-Sheet Credit Exposure, Policy [Policy Text Block]
Internal Credit Assessment [Domain]
External Credit Rating by Grouping [Domain]
us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue
Investment securities held to maturity, fair value, over 5 to 10 years
us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearFairValue
Investment securities held to maturity, fair value, 1 year or less
us-gaap_InterestIncomeSecuritiesTaxable
Taxable
us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue
Investment securities held to maturity, fair value, over 1 to 5 years
Other liabilities
Total other liabilities
Basis of Accounting, Policy [Policy Text Block]
us-gaap_InterestIncomeSecuritiesTaxExempt
Tax-exempt from regular federal income tax
us-gaap_CarryingValueOfSecuritiesSoldUnderRepurchaseAgreementsAndDepositsReceivedForSecuritiesLoaned
Total collateral carrying value
us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue
Debt securities held to maturity, fair value, without single date maturity
Cash and due from banks
us-gaap_Assets
Total Assets
Loans
us-gaap_InterestReceivableCurrent
Total interest receivable
us-gaap_InvestmentOwnedAtFairValue
Investment Owned, Fair Value
us-gaap_InterestAndDividendIncomeSecurities
Total interest income from investment securities
Diluted earnings (in dollars per share)
Diluted earnings per common share (in dollars per share)
us-gaap_InvestmentOwnedBalanceShares
Investment Owned, Balance, Shares
us-gaap_OtherRealEstate
Other Real Estate
Asset Class [Domain]
us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation
Excise tax on net common stock Repurchase
Other Liabilities [Table Text Block]
us-gaap_InterestPaidNet
Interest paid for the period
Visa Inc. [Member]
Represents information pertaining to Visa Inc.
wabc_PolicyTable
wabc_ConversionRateOfClassBCommonStockIntoClassACommonStock
Conversion Rate of Class B Common Stock into Class A Common Stock
Represents the conversion rate of class B common stock into class A common stock, with regard to an investment in the common stock of another entity.
Impaired Loans [Member]
All impaired loans (e.g. originated, purchased covered and purchased noncovered) that have been measured at fair value on a nonrecurring basis and a loss has been recorded or a specific allowance has been established.
wabc_AssetsFairValueDisclosureTotalLosses
Total Losses
Amount of losses recognized on assets measured at fair value.
us-gaap_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYearWriteoff
Originated prior, writeoff
us-gaap_FinancingReceivableExcludingAccruedInterestRevolvingWriteoff
Financing Receivable Revolving, Writeoff
us-gaap_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYearWriteoff
Originated three years before, writeoff
us-gaap_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYearWriteoff
Originated four years before, writeoff
us-gaap_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYearWriteoff
Originated one years before, writeoff
us-gaap_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYearWriteoff
Originated two years before, writeoff
us-gaap_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYearWriteoff
Originated current year, writeoff
Securities sold under repurchase agreements
Agency Residential MBS [Member]
Securities issued by government sponsored entities and collateralized by residential real estate mortgage loans.
Deposit Liabilities, Type [Table Text Block]
us-gaap_StockholdersEquity
Total Shareholders' Equity
Balance
Balance
Debt securities held to maturity
us-gaap_DebtSecuritiesHeldToMaturityAccruedInterestAfterAllowanceForCreditLoss
Loans
us-gaap_FinancingReceivableAccruedInterestAfterAllowanceForCreditLoss
Goodwill [Table Text Block]
Agency Commercial MBS [Member]
Securities issued by government sponsored entities and collateralized by commercial real estate mortgage loans.
us-gaap_PaymentsOfDividendsCommonStock
Common stock dividends paid
wabc_CollateralDependentLoansBalance
Collateral-dependent Loans, Balance
Represents the balance of collateral-dependent loans as of the specified date. A loan is considered collateral-dependent when the borrower is experiencing financial difficult and repayment is expected to be provided substantially through the operation or sale of the collateral.
Investment, Issuer Name [Axis]
wabc_NumberOfCollateralDependentLoans
Number of Collateral-dependent Loans
Represents the number of collateral-dependent loans as of the specified date.
Investment, Issuer Name [Domain]
Concentration Risk Benchmark [Axis]
Concentration Risk Benchmark [Domain]
BBB+/BBB [Member]
Relating to BBB+/BBB.
Consolidation, Less-than-Wholly-Owned Subsidiary, Parent Ownership Interest, Effect of Change [Table]
Right-of-use asset
us-gaap_OperatingLeaseRightOfUseAsset
Operating Lease, Right-of-Use Asset
Debt securities available for sale
us-gaap_DebtSecuritiesAvailableForSaleAccruedInterestAfterAllowanceForCreditLoss
Schedule of Repurchase Agreements [Table Text Block]
ecd_Rule10b51ArrTrmntdFlag
Rule 10b5-1 Arrangement Terminated [Flag]
us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax
Noninterest income revenue
ecd_Rule10b51ArrAdoptedFlag
Rule 10b5-1 Arrangement Adopted [Flag]
Fiduciary and Trust [Member]