Note 11 - Fair Value Measurements (Details Textual)	12 Months Ended
Dec. 31, 2021
Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Appraisal Rate	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