XML 41 R30.htm IDEA: XBRL DOCUMENT
v3.25.2

Note 3 - Investment Securities (Details Textual) - USD ($) $ in Thousands | Jun. 30, 2025 | Dec. 31, 2024 | Jun. 30, 2024 | Dec. 31, 2023
--- | --- | --- | --- | ---
Debt Securities, Held-to-Maturity, Allowance for Credit Loss, Excluding Accrued Interest | $ 1 | $ 1 | $ 1 | $ 1
Total, fair value | 4,044,168 | 4,203,648 |  |
Debt Securities, Held-to-Maturity, Excluding Accrued Interest, Nonaccrual | 0 |  |  |
Corporate Debt Securities [Member] |  |  |  |
Debt Securities, Held-to-Maturity, Allowance for Credit Loss, Excluding Accrued Interest | 0 |  |  |
Asset Pledged as Collateral [Member] | Public Deposits and Short-term Borrowed Funds [Member] |  |  |  |
Total, fair value | $ 1,935,926 | $ 2,049,954 |  |

X
- Definition Amount, excluding accrued interest, of allowance for credit loss on investment in debt security measured at amortized cost (held-to-maturity). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479344/326-20-45-1 + Details
Name: | us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossExcludingAccruedInterest
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount excluding accrued interest, of investment in debt security measured at amortized cost (held-to-maturity) on nonaccrual status. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 16 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479319/326-20-50-16 + Details
Name: | us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestNonaccrual
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition 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). + References No definition available. + Details
Name: | wabc_DebtSecuritiesAvailableforsaleAndHeldtomaturityBeforeAllowanceForCreditLoss
Namespace Prefix: | wabc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PledgedStatusAxis=us-gaap_AssetPledgedAsCollateralMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PledgingPurposeAxis=wabc_PublicDepositsAndShorttermBorrowedFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |