Note 8 - Deposits and Borrowed Funds (Details Textual) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2025
Demand Deposit Overdrafts	$ 735		$ 769
Interest Expense, Time Deposits, $100,000 or More	11	$ 17
Federal Reserve [Member]
Line of Credit Facility, Maximum Borrowing Capacity	765,854
Short-term Line of Credit	0
Corresponding Banks [Member]
Line of Credit Facility, Maximum Borrowing Capacity	$ 60,000

Interest expense incurred on time deposits, including certificates of deposits, of $100,000 or more in domestic offices.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(6))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478524/942-220-S99-1

+ Details

Name:	us-gaap_InterestExpenseTimeDeposits100000OrMore
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S50
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480657/210-10-S50-8

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(19)(b))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

+ Details

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

- Definition

Amounts honored in excess of customers account balances, recorded by the bank as a loan.

+ References

No definition available.

+ Details

Name:	wabc_DemandDepositOverdrafts
Namespace Prefix:	wabc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount of short-term line of credit outstanding.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=wabc_FederalReserveMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=wabc_CorrespondingBanksMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: