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Note 6 - Goodwill and Identifiable Intangible Assets (Details Textual) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2025	Dec. 31, 2024
Goodwill and Intangible Asset Impairment	$ 0	$ 0	$ 0
Amortization Expense, Adjustment Resulting from a Change in Estimates of Useful Lives or Residual Values	$ 0	$ 0	$ 0

X

- Definition

Total loss recognized during the period from the impairment of goodwill plus the loss recognized in the period resulting from the impairment of the carrying amount of intangible assets, other than goodwill.

+ References

No definition available.

+ Details

Name:	us-gaap_GoodwillAndIntangibleAssetImpairment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Represents the amount of adjustment made to amortization expense during the period as a result of a change in estimates of useful lives or residual values.

+ References

No definition available.

+ Details

Name:	wabc_AmortizationExpenseAdjustmentResultingFromAChangeInEstimatesOfUsefulLivesOrResidualValues
Namespace Prefix:	wabc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration