Note 2 - Accounting Policies	9 Months Ended
Sep. 30, 2011
Significant Accounting Policies [Text Block]	Note 2: Accounting Policies The Company’s accounting policies are discussed in Note 1 to the audited consolidated financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2010. Certain amounts in prior periods have been reclassified to conform to the current presentation. Nonmarketable Equity Securities. Nonmarketable equity securities include securities that are not publicly traded and securities acquired for various purposes, such as to meet regulatory requirements (for example, Federal Home Loan Bank and Federal Reserve stock). These securities are accounted for under the cost method and are included in other assets. The Company reviews those assets accounted for under the cost method at least quarterly for possible declines in value that are considered “other than temporary”. The Company’s review typically includes an analysis of the facts and circumstances of each investment, the expectations for the investment’s cash flows and capital needs, the viability of its business model and exit strategy. The asset value is reduced when a decline in value is considered to be other than temporary. The Company recognizes the estimated loss as a loss from equity investments in noninterest income. Certain accounting policies underlying the preparation of these financial statements require Management to make estimates and judgments. These estimates and judgments may significantly affect reported amounts of assets and liabilities, revenues and expenses, and disclosures of contingent assets and liabilities. Management exercises judgment to estimate the appropriate level of the allowance for credit losses and the acquisition date fair value of purchased loans, which are discussed in the Company’s accounting policies. As described in Note 3 below, Westamerica Bank (“Bank”) acquired assets and assumed liabilities of the former Sonoma Valley Bank (“Sonoma”) on August 20, 2010. The acquired assets and assumed liabilities were measured at estimated fair values, as required by Financial Accounting Standards Board (FASB) Accounting Standards Codification (ASC) 805, Business Combinations. Management made significant estimates and exercised significant judgment in accounting for the acquisition. Management judgmentally measured loan fair values based on loan file reviews (including borrower financial statements and tax returns), appraised collateral values, expected cash flows, and historical loss factors. Repossessed loan collateral was primarily valued based upon appraised collateral values. The Bank also recorded an identifiable intangible asset representing the value of the core deposit customer base of Sonoma based on Management’s evaluation of the cost of such deposits relative to alternative funding sources. In determining the value of the identifiable intangible asset, Management used significant estimates including average lives of depository accounts, future interest rate levels, the cost of servicing various depository products, and other significant estimates. Management used quoted market prices to determine the fair value of investment securities and FHLB advances. The acquired assets of Sonoma include loans; such loans are not indemnified by the Federal Deposit Insurance Corporation (“FDIC”). However, on February 6, 2009, the Bank acquired loans in a business combination that are indemnified by the FDIC, as described in Note 2 to the audited consolidated financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2010. Pursuant to acquisition accounting, the loans in each business combination were measured at their estimated fair value at the respective acquisition date. This method of measuring the carrying value of purchased loans differs from loans originated by the Company, and as such, the Company identifies purchased loans not indemnified by the FDIC as “Purchased Non-covered Loans” and purchased loans indemnified by the FDIC as “Purchased Covered Loans.” Loans originated by the Company are measured at the principal amount outstanding, net of unearned discount and unamortized deferred fees and costs. These loans are identified as “Originated Loans.” Recently Adopted Accounting Standards FASB Accounting Standards Update (ASU) 2011-02, A Creditor’s Determination of Whether a Restructuring is a Troubled Debt Restructuring, was issued April 2011 providing additional guidance for creditors in determining whether a creditor has granted a concession and whether a debtor is experiencing financial difficulties for purposes of determining whether a restructuring constitutes a troubled debt restructuring. The provisions of this standard are effective for the first interim or annual period beginning on or after June 15, 2011 with early adoption permissible, and should be applied retrospectively to the beginning of the annual period of adoption. The Company early adopted the provisions of this standard effective April 1, 2011 with retrospective application to January 1, 2011. One troubled debt restructuring was identified as a result of the adoption of this Update as disclosed in Note 5. FASB ASU 2011-01, Deferral of the Effective Date of Disclosures about Troubled Debt Restructurings in Update No. 2010-20 (Topic 310), was issued January 2011 deferring the new disclosure requirements (paragraphs 310-10-50-31 through 50-34 of the FASB Accounting Standards Codification) about troubled debt restructurings to be concurrent with the effective date of the guidance for determining what constitutes a troubled debt restructuring, as presented in proposed Accounting Standards Update, Receivables (Topic 310): Clarifications to Accounting for Troubled Debt Restructurings by Creditors. As a result of the issuance of Update 2011-02, the provisions of Update 2011-01 are effective for the first interim or annual period beginning on or after June 15, 2011 or July 1, 2011 for the Company, and should be applied retrospectively to the beginning of the annual period of adoption. The Company adopted the Update concurrent with ASU 2011-02. Recently Issued Accounting Standards FASB ASU 2011-03, Reconsideration of Effective Control for Repurchase Agreements, was issued April 2011 addressing the accounting for repurchase agreements and other agreements that both entitle and obligate a transferor to repurchase or redeem financial assets before their maturity. The amendments remove from the assessment of effective control (1) the criterion requiring the transferor to have the ability to repurchase or redeem the financial assets on substantially the agreed terms, even in the event of default by the transferee, and (2) the collateral maintenance implementation guidance related to that criterion. The provisions of this Update are effective for the first interim or annual period beginning on or after December 15, 2011, and should be applied prospectively to transactions or modifications of existing transactions that occur on or after the effective date. Management does not expect the adoption of the Update to have a material effect on the Company’s financial statements at the date of adoption. FASB ASU 2011-04, Amendments to Achieve Common Fair Value Measurement and Disclosure Requirements in U.S. GAAP and IFRSs, was issued May 2011 as a result of the FASB and International Accounting Standards Board’s (IASB) goal to develop common requirements for measuring fair value and for disclosing information about fair value measurements in accordance with U.S. generally accepted accounting principles and International Financial Reporting Standards. The provisions of this Update are effective during the interim or annual periods beginning after December 15, 2011, and are to be applied prospectively. Management does not expect the adoption of the Update to have a material effect on the Company’s financial statements at the date of adoption. FASB ASU 2011-05, Presentation of Comprehensive Income, was issued June 2011 requiring that all changes in stockholders’ equity be presented either in a single continuous statement of comprehensive income or in two separate but consecutive statements. This Update also requires that reclassification adjustments for items that are reclassified from other comprehensive income to net income be presented on the face of the financial statements. The provisions of this Update are effective for fiscal years, and interim periods within those years, beginning after December 15, 2011, and are to be applied retrospectively. Early adoption is permitted. Management does not expect the adoption of the Update to have a material effect on the Company’s financial statements at the date of adoption. FASB Accounting Standards Update (ASU) 2011-08, Testing for Goodwill Impairment, was issued September 2011 giving an entity the option to first assess qualitative factors to determine whether the existence of events or circumstances leads to a determination that it is more likely than not that the fair value of a reporting unit is less than its carrying amount. If, after assessing the totality of events or circumstances, an entity determines it is more likely than not that the fair value of a reporting unit is more than its carrying amount, then performing the two-step impairment test is unnecessary. However, if an entity concludes otherwise, then it is required to perform the first step of the two-step impairment test by calculating the fair value of the reporting unit and comparing the fair value with the carrying amount of the reporting unit. If the carrying amount of a reporting unit exceeds its fair value, then the entity is required to perform the second step of the goodwill impairment test to measure the amount of the impairment loss, if any. Under the amendments in this Update, an entity has the option to bypass the qualitative assessment for any reporting unit in any period and proceed directly to performing the first step of the two-step goodwill impairment test. An entity may resume performing the qualitative assessment in any subsequent period. The provisions of this standard are effective for annual and interim goodwill impairment tests performed for fiscal years beginning after December 15, 2011, with early adoption permitted. Management does not expect the adoption of the Update to have a material effect on the Company’s financial statements at the date of adoption.

Note 2 - Accounting Policies

9 Months Ended

Sep. 30, 2011

Significant Accounting Policies [Text Block]

Note 2: Accounting Policies

The Company’s accounting policies are discussed in Note 1 to the audited consolidated financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2010. Certain amounts in prior periods have been reclassified to conform to the current presentation.

Nonmarketable Equity Securities. Nonmarketable equity securities include securities that are not publicly traded and securities acquired for various purposes, such as to meet regulatory requirements (for example, Federal Home Loan Bank and Federal Reserve stock). These securities are accounted for under the cost method and are included in other assets. The Company reviews those assets accounted for under the cost method at least quarterly for possible declines in value that are considered “other than temporary”. The Company’s review typically includes an analysis of the facts and circumstances of each investment, the expectations for the investment’s cash flows and capital needs, the viability of its business model and exit strategy. The asset value is reduced when a decline in value is considered to be other than temporary. The Company recognizes the estimated loss as a loss from equity investments in noninterest income.

Certain accounting policies underlying the preparation of these financial statements require Management to make estimates and judgments. These estimates and judgments may significantly affect reported amounts of assets and liabilities, revenues and expenses, and disclosures of contingent assets and liabilities. Management exercises judgment to estimate the appropriate level of the allowance for credit losses and the acquisition date fair value of purchased loans, which are discussed in the Company’s accounting policies.

As described in Note 3 below, Westamerica Bank (“Bank”) acquired assets and assumed liabilities of the former Sonoma Valley Bank (“Sonoma”) on August 20, 2010. The acquired assets and assumed liabilities were measured at estimated fair values, as required by Financial Accounting Standards Board (FASB) Accounting Standards Codification (ASC) 805, Business Combinations. Management made significant estimates and exercised significant judgment in accounting for the acquisition. Management judgmentally measured loan fair values based on loan file reviews (including borrower financial statements and tax returns), appraised collateral values, expected cash flows, and historical loss factors. Repossessed loan collateral was primarily valued based upon appraised collateral values. The Bank also recorded an identifiable intangible asset representing the value of the core deposit customer base of Sonoma based on Management’s evaluation of the cost of such deposits relative to alternative funding sources. In determining the value of the identifiable intangible asset, Management used significant estimates including average lives of depository accounts, future interest rate levels, the cost of servicing various depository products, and other significant estimates. Management used quoted market prices to determine the fair value of investment securities and FHLB advances.

The acquired assets of Sonoma include loans; such loans are not indemnified by the Federal Deposit Insurance Corporation (“FDIC”). However, on February 6, 2009, the Bank acquired loans in a business combination that are indemnified by the FDIC, as described in Note 2 to the audited consolidated financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2010. Pursuant to acquisition accounting, the loans in each business combination were measured at their estimated fair value at the respective acquisition date. This method of measuring the carrying value of purchased loans differs from loans originated by the Company, and as such, the Company identifies purchased loans not indemnified by the FDIC as “Purchased Non-covered Loans” and purchased loans indemnified by the FDIC as “Purchased Covered Loans.”

Loans originated by the Company are measured at the principal amount outstanding, net of unearned discount and unamortized deferred fees and costs. These loans are identified as “Originated Loans.”

Recently Adopted Accounting Standards

FASB Accounting Standards Update (ASU) 2011-02, A Creditor’s Determination of Whether a Restructuring is a Troubled Debt Restructuring, was issued April 2011 providing additional guidance for creditors in determining whether a creditor has granted a concession and whether a debtor is experiencing financial difficulties for purposes of determining whether a restructuring constitutes a troubled debt restructuring. The provisions of this standard are effective for the first interim or annual period beginning on or after June 15, 2011 with early adoption permissible, and should be applied retrospectively to the beginning of the annual period of adoption. The Company early adopted the provisions of this standard effective April 1, 2011 with retrospective application to January 1, 2011. One troubled debt restructuring was identified as a result of the adoption of this Update as disclosed in Note 5.

FASB ASU 2011-01, Deferral of the Effective Date of Disclosures about Troubled Debt Restructurings in Update No. 2010-20 (Topic 310), was issued January 2011 deferring the new disclosure requirements (paragraphs 310-10-50-31 through 50-34 of the FASB Accounting Standards Codification) about troubled debt restructurings to be concurrent with the effective date of the guidance for determining what constitutes a troubled debt restructuring, as presented in proposed Accounting Standards Update, Receivables (Topic 310): Clarifications to Accounting for Troubled Debt Restructurings by Creditors. As a result of the issuance of Update 2011-02, the provisions of Update 2011-01 are effective for the first interim or annual period beginning on or after June 15, 2011 or July 1, 2011 for the Company, and should be applied retrospectively to the beginning of the annual period of adoption. The Company adopted the Update concurrent with ASU 2011-02.

Recently Issued Accounting Standards

FASB ASU 2011-03, Reconsideration of Effective Control for Repurchase Agreements, was issued April 2011 addressing the accounting for repurchase agreements and other agreements that both entitle and obligate a transferor to repurchase or redeem financial assets before their maturity. The amendments remove from the assessment of effective control (1) the criterion requiring the transferor to have the ability to repurchase or redeem the financial assets on substantially the agreed terms, even in the event of default by the transferee, and (2) the collateral maintenance implementation guidance related to that criterion. The provisions of this Update are effective for the first interim or annual period beginning on or after December 15, 2011, and should be applied prospectively to transactions or modifications of existing transactions that occur on or after the effective date. Management does not expect the adoption of the Update to have a material effect on the Company’s financial statements at the date of adoption.

FASB ASU 2011-04, Amendments to Achieve Common Fair Value Measurement and Disclosure Requirements in U.S. GAAP and IFRSs, was issued May 2011 as a result of the FASB and International Accounting Standards Board’s (IASB) goal to develop common requirements for measuring fair value and for disclosing information about fair value measurements in accordance with U.S. generally accepted accounting principles and International Financial Reporting Standards. The provisions of this Update are effective during the interim or annual periods beginning after December 15, 2011, and are to be applied prospectively. Management does not expect the adoption of the Update to have a material effect on the Company’s financial statements at the date of adoption.

FASB ASU 2011-05, Presentation of Comprehensive Income, was issued June 2011 requiring that all changes in stockholders’ equity be presented either in a single continuous statement of comprehensive income or in two separate but consecutive statements. This Update also requires that reclassification adjustments for items that are reclassified from other comprehensive income to net income be presented on the face of the financial statements. The provisions of this Update are effective for fiscal years, and interim periods within those years, beginning after December 15, 2011, and are to be applied retrospectively. Early adoption is permitted. Management does not expect the adoption of the Update to have a material effect on the Company’s financial statements at the date of adoption.

FASB Accounting Standards Update (ASU) 2011-08, Testing for Goodwill Impairment, was issued September 2011 giving an entity the option to first assess qualitative factors to determine whether the existence of events or circumstances leads to a determination that it is more likely than not that the fair value of a reporting unit is less than its carrying amount. If, after assessing the totality of events or circumstances, an entity determines it is more likely than not that the fair value of a reporting unit is more than its carrying amount, then performing the two-step impairment test is unnecessary. However, if an entity concludes otherwise, then it is required to perform the first step of the two-step impairment test by calculating the fair value of the reporting unit and comparing the fair value with the carrying amount of the reporting unit. If the carrying amount of a reporting unit exceeds its fair value, then the entity is required to perform the second step of the goodwill impairment test to measure the amount of the impairment loss, if any. Under the amendments in this Update, an entity has the option to bypass the qualitative assessment for any reporting unit in any period and proceed directly to performing the first step of the two-step goodwill impairment test. An entity may resume performing the qualitative assessment in any subsequent period. The provisions of this standard are effective for annual and interim goodwill impairment tests performed for fiscal years beginning after December 15, 2011, with early adoption permitted. Management does not expect the adoption of the Update to have a material effect on the Company’s financial statements at the date of adoption.