Organization and Summary of Significant Accounting and Reporting Policies	9 Months Ended
Sep. 30, 2012
Organization and Summary of Significant Accounting and Reporting Policies [Abstract]
Organization and Summary of Significant Accounting and Reporting Policies	1. 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 2011 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. Certain reclassifications have been made to the 2011 financial statements to conform to the classifications used in 2012. New Accounting Standards: In September 2011, the FASB issued ASU 2011-08, Intangibles - Goodwill and Other (Topic 350) - Testing Goodwill for Impairment. ASU 2011-08 amends Topic 350, Intangibles – Goodwill and Other, to give entities 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 not more likely than not that the fair value of a reporting unit is less 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. ASU 2011-08 is effective for annual and interim impairment tests beginning after December 15, 2011, and did not have a significant impact on the Company's financial statements. In April 2011, the FASB issued ASU No. 2011-02, Receivables (Topic 310): A Creditor's Determination of Whether a Restructuring Is a Troubled Debt Restructuring. ASU 2011-02 clarifies the guidance in ASC 310-40 Receivables: Troubled Debt Restructurings by Creditors. Creditors are required to identify a restructuring as a troubled debt restructuring if the restructuring constitutes a concession and the debtor is experiencing financial difficulties. ASU 2011-02 clarifies guidance on whether a creditor has granted a concession and clarifies the guidance on a creditor's evaluation of whether a debtor is experiencing financial difficulties. In addition, ASU 2011-02 also precludes the creditor from using the effective interest rate test in the debtor's guidance on restructuring of payables when evaluating whether a restructuring constitutes a troubled debt restructuring. The effective date of ASU 2011-2 for public entities is effective for the first interim or annual period beginning on or after June 15, 2011, and should be applied retrospectively to the beginning of the annual period of adoption. If, as a result of adoption, an entity identifies newly impaired receivables, an entity should apply the amendments for purposes of measuring impairment prospectively for the first interim or annual period beginning on or after June 15, 2011. The Company adopted the methodologies prescribed by this ASU during the third quarter 2011 and it did not have a material effect on its financial statements. In April 2011, the FASB issued ASU 2011-03, Reconsideration of Effective Control for Repurchase Agreements. This ASU was developed to improve the accounting for repurchase agreements (repos) and other agreements that both entitle and obligate a transferor to repurchase or redeem financial assets before their maturity. The amendments in this ASU 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 amendments in this ASU apply to all entities, both public and nonpublic. The amendments affect all entities that enter into agreements to transfer financial assets that both entitle and obligate the transferor to repurchase or redeem the financial assets before their maturity. The guidance in this ASU is 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. Early adoption is not permitted. This ASU did not have a significant impact on the Company's financial statements. In May 2011, the FASB issued ASU 2011-04, Amendments to Achieve Common Fair Value Measurement and Disclosure Requirements in U.S. GAAP and IFRSs. The amendments in this ASU result in common fair value measurement and disclosure requirements in U.S. GAAP and IFRSs. Consequently, the amendments change the wording used to describe many of the requirements in U.S. GAAP for measuring fair value and for disclosing information about fair value measurements. The amendments in this ASU are to be applied prospectively. For public entities, the amendments are effective during interim and annual periods beginning after December 15, 2011. Early application by public entities is not permitted. This ASU did not have a significant impact on the Company's financial statements. In June 2011, the FASB issued ASU No. 2011-05, Presentation of Comprehensive Income. ASU 2011-05 requires entities to present the total of comprehensive income, the components of net income and the components of other comprehensive income in a single continuous statement of comprehensive income or in two separate consecutive statements. The effective date for ASU 2011-05 is for the first interim or annual period beginning on or after December 15, 2011. The adoption of ASU 2011-05 did not have a material impact on the Company's results of operations or financial position.

1. 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 2011 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.

Certain reclassifications have been made to the 2011 financial statements to conform to the classifications used in 2012.

New Accounting Standards:

In September 2011, the FASB issued ASU 2011-08, Intangibles - Goodwill and Other (Topic 350) - Testing Goodwill for Impairment. ASU 2011-08 amends Topic 350, Intangibles – Goodwill and Other, to give entities 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 not more likely than not that the fair value of a reporting unit is less 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. ASU 2011-08 is effective for annual and interim impairment tests beginning after December 15, 2011, and did not have a significant impact on the Company's financial statements.

In April 2011, the FASB issued ASU No. 2011-02, Receivables (Topic 310): A Creditor's Determination of Whether a Restructuring Is a Troubled Debt Restructuring. ASU 2011-02 clarifies the guidance in ASC 310-40 Receivables: Troubled Debt Restructurings by Creditors. Creditors are required to identify a restructuring as a troubled debt restructuring if the restructuring constitutes a concession and the debtor is experiencing financial difficulties. ASU 2011-02 clarifies guidance on whether a creditor has granted a concession and clarifies the guidance on a creditor's evaluation of whether a debtor is experiencing financial difficulties. In addition, ASU 2011-02 also precludes the creditor from using the effective interest rate test in the debtor's guidance on restructuring of payables when evaluating whether a restructuring constitutes a troubled debt restructuring. The effective date of ASU 2011-2 for public entities is effective for the first interim or annual period beginning on or after June 15, 2011, and should be applied retrospectively to the beginning of the annual period of adoption. If, as a result of adoption, an entity identifies newly impaired receivables, an entity should apply the amendments for purposes of measuring impairment prospectively for the first interim or annual period beginning on or after June 15, 2011. The Company adopted the methodologies prescribed by this ASU during the third quarter 2011 and it did not have a material effect on its financial statements.

In April 2011, the FASB issued ASU 2011-03, Reconsideration of Effective Control for Repurchase Agreements. This ASU was developed to improve the accounting for repurchase agreements (repos) and other agreements that both entitle and obligate a transferor to repurchase or redeem financial assets before their maturity. The amendments in this ASU 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 amendments in this ASU apply to all entities, both public and nonpublic. The amendments affect all entities that enter into agreements to transfer financial assets that both entitle and obligate the transferor to repurchase or redeem the financial assets before their maturity. The guidance in this ASU is 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. Early adoption is not permitted. This ASU did not have a significant impact on the Company's financial statements.

In May 2011, the FASB issued ASU 2011-04, Amendments to Achieve Common Fair Value Measurement and Disclosure Requirements in U.S. GAAP and IFRSs. The amendments in this ASU result in common fair value measurement and disclosure requirements in U.S. GAAP and IFRSs. Consequently, the amendments change the wording used to describe many of the requirements in U.S. GAAP for measuring fair value and for disclosing information about fair value measurements. The amendments in this ASU are to be applied prospectively. For public entities, the amendments are effective during interim and annual periods beginning after December 15, 2011. Early application by public entities is not permitted. This ASU did not have a significant impact on the Company's financial statements.

In June 2011, the FASB issued ASU No. 2011-05, Presentation of Comprehensive Income. ASU 2011-05 requires entities to present the total of comprehensive income, the components of net income and the components of other comprehensive income in a single continuous statement of comprehensive income or in two separate consecutive statements. The effective date for ASU 2011-05 is for the first interim or annual period beginning on or after December 15, 2011. The adoption of ASU 2011-05 did not have a material impact on the Company's results of operations or financial position.