Organization and Summary of Significant Accounting and Reporting Policies	9 Months Ended
Sep. 30, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Summary of Significant Accounting and Reporting Policies	Organization and Summary of Significant Accounting and Reporting Policies The consolidated financial statements include the accounts of United Security Bancshares, and its wholly owned subsidiary United Security Bank (the “Bank”) and two bank subsidiaries, USB Investment Trust (the “REIT”) and United Security Emerging Capital Fund (collectively the “Company” or “USB”). Intercompany accounts and transactions have been eliminated in consolidation. These unaudited financial statements have been prepared in accordance with generally accepted accounting principles for interim financial information on a basis consistent with the accounting policies reflected in the audited financial statements of the Company included in its 2014 Annual Report on Form 10-K. These interim financial statements do not include all of the information and footnotes required by generally accepted accounting principles for complete financial statements. In the opinion of management, all adjustments (consisting of a normal, recurring nature) considered necessary for a fair presentation have been included. Operating results for the interim periods presented are not necessarily indicative of the results that may be expected for any other interim period or for the year as a whole. Recently Issued Accounting Standards: In January 2014, FASB issued ASU 2014-04, Receivables - Troubled Debt Restructurings by Creditors. The amendments in this ASU clarify that an in substance repossession or foreclosure occurs, and a creditor is considered to have received physical possession of residential real estate property collateralizing a consumer mortgage loan, upon either (1) the creditor obtaining legal title to the residential real estate property upon completion of a foreclosure or (2) the borrower conveying all interest in the residential real estate property to the creditor to satisfy that loan through completion of a deed in lieu of foreclosure or through a similar legal agreement. Additionally, the amendments require interim and annual disclosure of both (1) the amount of foreclosed residential real estate property held by the creditor and (2) the recorded investment in consumer mortgage loans collateralized by residential real estate property that are in the process of foreclosure according to local requirements of the applicable jurisdiction. The amendments in this ASU are effective for public business entities for annual periods, and interim periods within those annual periods, beginning after December 15, 2014. An entity can elect to adopt the amendments in this ASU using either a modified retrospective transition method or a prospective transition method. Early adoption is permitted. The adoption of this update did not have a significant impact on the Company’s consolidated financial statements. In January 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2014-01 Accounting for Investments in Qualified Affordable Housing Projects. This ASU provides "guidance on accounting for investments by a reporting entity in flow-through limited liability entities that manage or invest in affordable housing projects that qualify for the low-income housing tax credit." It allows the proportional amortization method to be used by a reporting entity if certain conditions are met. The ASU also defines when a qualified affordable housing project through a limited liability entity should be tested for impairment. If a qualified affordable housing project does not meet the conditions for using the proportional amortization method, the investment should be accounted for using an equity method investment or a cost method investment. The ASU is effective for fiscal years beginning after December 15, 2014, and interim periods therein. The Company will continue to account for our low-income housing tax credit investments using the equity method subsequent to the adoption of ASU 2014-01 and does not expect any impact on the Company's consolidated financial statements.

Organization and Summary of Significant Accounting and Reporting Policies

The consolidated financial statements include the accounts of United Security Bancshares, and its wholly owned subsidiary United Security Bank (the “Bank”) and two bank subsidiaries, USB Investment Trust (the “REIT”) and United Security Emerging Capital Fund (collectively the “Company” or “USB”). Intercompany accounts and transactions have been eliminated in consolidation.

These unaudited financial statements have been prepared in accordance with generally accepted accounting principles for interim financial information on a basis consistent with the accounting policies reflected in the audited financial statements of the Company included in its 2014 Annual Report on Form 10-K. These interim financial statements do not include all of the information and footnotes required by generally accepted accounting principles for complete financial statements. In the opinion of management, all adjustments (consisting of a normal, recurring nature) considered necessary for a fair presentation have been included. Operating results for the interim periods presented are not necessarily indicative of the results that may be expected for any other interim period or for the year as a whole.

Recently Issued Accounting Standards:

In January 2014, FASB issued ASU 2014-04, Receivables - Troubled Debt Restructurings by Creditors. The amendments in this ASU clarify that an in substance repossession or foreclosure occurs, and a creditor is considered to have received physical possession of residential real estate property collateralizing a consumer mortgage loan, upon either (1) the creditor obtaining legal title to the residential real estate property upon completion of a foreclosure or (2) the borrower conveying all interest in the residential real estate property to the creditor to satisfy that loan through completion of a deed in lieu of foreclosure or through a similar legal agreement. Additionally, the amendments require interim and annual disclosure of both (1) the amount of foreclosed residential real estate property held by the creditor and (2) the recorded investment in consumer mortgage loans collateralized by residential real estate property that are in the process of foreclosure according to local requirements of the applicable jurisdiction. The amendments in this ASU are effective for public business entities for annual periods, and interim periods within those annual periods, beginning after December 15, 2014. An entity can elect to adopt the amendments in this ASU using either a modified retrospective transition method or a prospective transition method. Early adoption is permitted. The adoption of this update did not have a significant impact on the Company’s consolidated financial statements.

In January 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2014-01 Accounting for Investments in Qualified Affordable Housing Projects. This ASU provides "guidance on accounting for investments by a reporting entity in flow-through limited liability entities that manage or invest in affordable housing projects that qualify for the low-income housing tax credit." It allows the proportional amortization method to be used by a reporting entity if certain conditions are met. The ASU also defines when a qualified affordable housing project through a limited liability entity should be tested for impairment. If a qualified affordable housing project does not meet the conditions for using the proportional amortization method, the investment should be accounted for using an equity method investment or a cost method investment. The ASU is effective for fiscal years beginning after December 15, 2014, and interim periods therein. The Company will continue to account for our low-income housing tax credit investments using the equity method subsequent to the adoption of ASU 2014-01 and does not expect any impact on the Company's consolidated financial statements.