Note 9 - Fair Value Measurements (Details Textual)	3 Months Ended	6 Months Ended
Jun. 30, 2024	Jun. 30, 2024
Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Appraisal Rate	10.00%	10.00%

Represents the percentage of the appraisal value that is cost estimated to dispose of collateral.

No definition available.

Name:	wabc_FairValueInputsAppraisalRate
Namespace Prefix:	wabc_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration