Note 12 - Commitments and Contingent Liabilities (Details Textual) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Loan Commitments, Not Unconditionally Cancellable	$ 29,958	$ 31,889
Unfunded Loan Commitments	206,028	202,696
Guarantor Obligations, Current Carrying Value	1,000	950
Other Liabilities [Member]
Reserve for Unfunded Commitments	201	201
Financial Standby Letter of Credit [Member]
Letters of Credit Outstanding, Amount	2,044	1,948
Commercial Standby Letters of Credit [Member]
Letters of Credit Outstanding, Amount	$ 95	$ 95

The current carrying amount of the liability for the freestanding or embedded guarantor's obligations under the guarantee or each group of similar guarantees.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482425/460-10-50-4

+ Details

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

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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

- Definition

The portion of loan commitments that are not unconditionally cancellable.

+ References

No definition available.

+ Details

Name:	wabc_LoanCommitmentsNotUnconditionallyCancellable
Namespace Prefix:	wabc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of reserve for unfunded commitments.

+ References

No definition available.

+ Details

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Namespace Prefix:	wabc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Reflects the unfunded portion of contractual agreements to lend funds to borrowers.

+ References

No definition available.

+ Details

Name:	wabc_UnfundedLoanCommitments
Namespace Prefix:	wabc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

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Namespace Prefix:
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- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

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