Note 10 - Commitments and Contingent Liabilities (Details Textual) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Loan Commitments, Not Unconditionally Cancellable	$ 33,342
Unfunded Loan Commitments	217,756	$ 233,850
Guarantor Obligations, Current Carrying Value	880	580
Other Liabilities [Member]
Reserve for Unfunded Commitments	201	201
Financial Standby Letter of Credit [Member]
Letters of Credit Outstanding, Amount	1,878	3,693
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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (c)
-URI https://asc.fasb.org/extlink&oid=124440162&loc=d3e12069-110248

+ 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

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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
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- Details

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