Note 9 - Risk-Based Capital (Details) - Capital Ratios for the Company and the Bank (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Consolidated Entities [Member]
Total Capital (to risk-weighted assets)
Amount (in Dollars)	$ 446,331		$ 444,205
Ratio	16.18%		16.33%
For Capital Adequacy Purposes, Amount (in Dollars)	220,745		217,627
For Capital Adequacy Purposes, Ratio	8.00%		8.00%
To Be Well Capitalized Under the FDICIA Prompt Corrective Action Provisions, Amount (in Dollars)	275,931		272,033
To Be Well Capitalized Under the FDICIA Prompt Corrective Action Provisions, Ratio	10.00%		10.00%
Tier 1 Capital (to risk-weighted assets)
Amount (in Dollars)	405,798		409,763
Ratio	14.71%		15.06%
For Capital Adequacy Purposes, Amount (in Dollars)	110,372		108,813
For Capital Adequacy Purposes, Ratio	4.00%		4.00%
To Be Well Capitalized Under the FDICIA Prompt Corrective Action Provisions, Amount (in Dollars)	165,559		163,220
To Be Well Capitalized Under the FDICIA Prompt Corrective Action Provisions, Ratio	6.00%		6.00%
Leverage Ratio *
Amount (in Dollars)	405,798	[1]	409,763	[1]
Ratio	8.55%	[1]	8.56%	[1]
For Capital Adequacy Purposes, Amount (in Dollars)	189,762	[1]	191,396	[1]
For Capital Adequacy Purposes, Ratio	4.00%	[1]	4.00%	[1]
To Be Well Capitalized Under the FDICIA Prompt Corrective Action Provisions, Amount (in Dollars)	237,203	[1]	239,245	[1]
To Be Well Capitalized Under the FDICIA Prompt Corrective Action Provisions, Ratio	5.00%	[1]	5.00%	[1]
Westamerica Bank [Member]
Total Capital (to risk-weighted assets)
Amount (in Dollars)	406,418		418,746
Ratio	14.93%		15.62%
For Capital Adequacy Purposes, Amount (in Dollars)	217,730		214,452
For Capital Adequacy Purposes, Ratio	8.00%		8.00%
To Be Well Capitalized Under the FDICIA Prompt Corrective Action Provisions, Amount (in Dollars)	272,162		268,065
To Be Well Capitalized Under the FDICIA Prompt Corrective Action Provisions, Ratio	10.00%		10.00%
Tier 1 Capital (to risk-weighted assets)
Amount (in Dollars)	360,809		378,921
Ratio	13.26%		14.14%
For Capital Adequacy Purposes, Amount (in Dollars)	108,865		107,226
For Capital Adequacy Purposes, Ratio	4.00%		4.00%
To Be Well Capitalized Under the FDICIA Prompt Corrective Action Provisions, Amount (in Dollars)	163,297		160,839
To Be Well Capitalized Under the FDICIA Prompt Corrective Action Provisions, Ratio	6.00%		6.00%
Leverage Ratio *
Amount (in Dollars)	360,809	[1]	378,921	[1]
Ratio	7.67%	[1]	7.99%	[1]
For Capital Adequacy Purposes, Amount (in Dollars)	188,109	[1]	189,788	[1]
For Capital Adequacy Purposes, Ratio	4.00%	[1]	4.00%	[1]
To Be Well Capitalized Under the FDICIA Prompt Corrective Action Provisions, Amount (in Dollars)	$ 235,137	[1]	$ 237,236	[1]
To Be Well Capitalized Under the FDICIA Prompt Corrective Action Provisions, Ratio	5.00%	[1]	5.00%	[1]

[1] The leverage ratio consists of Tier 1 capital divided by average assets, excluding certain intangible assets, during the most recent calendar quarter. The minimum leverage ratio guideline is 3.00% for banking organizations that do not anticipate significant growth and that have well-diversified risk, excellent asset quality, high liquidity, good earnings and, in general, are considered top-rated, strong banking organizations.