Organization and Summary of Significant Accounting and Reporting Policies	9 Months Ended
Sep. 30, 2016
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 2015 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 June 2016, FASB issued ASU 2016-13, Financial Instruments- Credit Losses (Topic 326). The FASB is issuing this Update to improve financial reporting by requiring timelier recording of credit losses on loans and other financial instruments held by financial institutions and other organizations. The Update requires enhanced disclosures and judgments in estimating credit losses and also amends the accounting for credit losses on available-for-sale debt securities and purchased financial assets with credit deterioration. This amendment is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. We are currently evaluating the impacts of this ASU on the consolidated financial statements. In March 2016, FASB issued ASU 2016-09, Compensation-Stock Compensation (Topic 718). The Board is issuing this Update as part of its Simplification Initiative. The objective of the Simplification Initiative is to identify, evaluate, and improve areas of generally accepted accounting principles (GAAP) for which cost and complexity can be reduced while maintaining or improving the usefulness of the information provided to users of financial statements. The areas for simplification in this Update were identified through outreach for the Simplification Initiative, pre-agenda research for the Private Company Council, and the August 2014 Post-Implementation Review Report on FASB No. 123(R), Share-Based Payment. This ASU is effective for annual reporting periods beginning after December 15, 2016, including interim periods within those annual reporting periods. We are currently evaluating the impacts of this ASU on the consolidated financial statements. In February 2016, FASB issued ASU 2016-02, Leases (Topic 842). The FASB is issuing this Update to increase transparency and comparability among organizations by recognizing lease assets and lease liabilities on the balance sheet and disclosing key information about leasing arrangements. To meet that objective, the FASB is amending the FASB Accounting Standards Codification® and creating Topic 842, Leases. This Update, along with IFRS 16, Leases, are the results of the FASB’s and the International Accounting Standards Board’s (IASB’s) efforts to meet that objective and improve financial reporting. This ASU will be effective for public business entities for annual periods beginning after December 15, 2018 (i.e., calendar periods beginning on January 1, 2019), and interim periods therein. We are currently evaluating the impacts of this ASU on the consolidated financial statements. In January 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2016-01 Financial Instruments-Overall: Recognition and Measurements of Financial Assets and Financial Liabilities. This ASU requires equity investments to be measured at fair value, with changes in fair value recognized in net income. The amendment also simplifies the impairment assessment of equity investments for which fair value is not readily determinable by requiring an entity to perform a qualitative assessment to identify impairment. The ASU is effective for fiscal years beginning after December 15, 2017, and interim periods therein. We are currently evaluating the impacts of this ASU on the consolidated financial statements. We are currently evaluating the impacts of this ASU on the consolidated financial statements, however, we believe the accounting and reporting for our mutual fund investments will be impacted. In September 2015, FASB issued ASU 2015-16, Business Combinations (Topic 805) -Simplifying the Accounting for Measurement-Period Adjustments. GAAP requires that during the amendment period, the acquirer retrospectively adjust the provisional amounts recognized at the acquisition date with a corresponding adjustment to goodwill. Those adjustments are required when new information is obtained about facts and circumstances that existed as of the acquisition date that, if known, would have affected the measurement of the amounts initially recognized or would have resulted in the recognition of additional assets or liabilities. To simplify the accounting for adjustments made to provisional amounts recognized in a business combination, the amendments in this Update eliminate the requirement to retrospectively account for those adjustments. These amendments in this Update are effective for fiscal years beginning after December 15, 2015. The Company does not expect any impact on the Company's consolidated financial statements resulting from the adoption of the update.

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 2015 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 June 2016, FASB issued ASU 2016-13, Financial Instruments- Credit Losses (Topic 326). The FASB is issuing this Update to improve financial reporting by requiring timelier recording of credit losses on loans and other financial instruments held by financial institutions and other organizations. The Update requires enhanced disclosures and judgments in estimating credit losses and also amends the accounting for credit losses on available-for-sale debt securities and purchased financial assets with credit deterioration. This amendment is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. We are currently evaluating the impacts of this ASU on the consolidated financial statements.

In March 2016, FASB issued ASU 2016-09, Compensation-Stock Compensation (Topic 718). The Board is issuing this Update as part of its Simplification Initiative. The objective of the Simplification Initiative is to identify, evaluate, and improve areas of generally accepted accounting principles (GAAP) for which cost and complexity can be reduced while maintaining or improving the usefulness of the information provided to users of financial statements. The areas for simplification in this Update were identified through outreach for the Simplification Initiative, pre-agenda research for the Private Company Council, and the August 2014 Post-Implementation Review Report on FASB No. 123(R), Share-Based Payment. This ASU is effective for annual reporting periods beginning after December 15, 2016, including interim periods within those annual reporting periods. We are currently evaluating the impacts of this ASU on the consolidated financial statements.

In February 2016, FASB issued ASU 2016-02, Leases (Topic 842). The FASB is issuing this Update to increase transparency and comparability among organizations by recognizing lease assets and lease liabilities on the balance sheet and disclosing key information about leasing arrangements. To meet that objective, the FASB is amending the FASB Accounting Standards Codification® and creating Topic 842, Leases. This Update, along with IFRS 16, Leases, are the results of the FASB’s and the International Accounting Standards Board’s (IASB’s) efforts to meet that objective and improve financial reporting. This ASU will be effective for public business entities for annual periods beginning after December 15, 2018 (i.e., calendar periods beginning on January 1, 2019), and interim periods therein. We are currently evaluating the impacts of this ASU on the consolidated financial statements.

In January 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2016-01 Financial Instruments-Overall: Recognition and Measurements of Financial Assets and Financial Liabilities. This ASU requires equity investments to be measured at fair value, with changes in fair value recognized in net income. The amendment also simplifies the impairment assessment of equity investments for which fair value is not readily determinable by requiring an entity to perform a qualitative assessment to identify impairment. The ASU is effective for fiscal years beginning after December 15, 2017, and interim periods therein. We are currently evaluating the impacts of this ASU on the consolidated financial statements. We are currently evaluating the impacts of this ASU on the consolidated financial statements, however, we believe the accounting and reporting for our mutual fund investments will be impacted.

In September 2015, FASB issued ASU 2015-16, Business Combinations (Topic 805) -Simplifying the Accounting for Measurement-Period Adjustments. GAAP requires that during the amendment period, the acquirer retrospectively adjust the provisional amounts recognized at the acquisition date with a corresponding adjustment to goodwill. Those adjustments are required when new information is obtained about facts and circumstances that existed as of the acquisition date that, if known, would have affected the measurement of the amounts initially recognized or would have resulted in the recognition of additional assets or liabilities. To simplify the accounting for adjustments made to provisional amounts recognized in a business combination, the amendments in this Update eliminate the requirement to retrospectively account for those adjustments. These amendments in this Update are effective for fiscal years beginning after December 15, 2015. The Company does not expect any impact on the Company's consolidated financial statements resulting from the adoption of the update.