Note 16 - Regulatory Matters (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2013	Dec. 31, 2012
Regulatory Matters [Abstract]
Federal Reserve Bank, Average Balance Deposit	$ 304,834	$ 345,772

The daily average of the deposit at the Federal Reserve Bank during the reporting period.

No definition available.

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