Organization and Summary of Significant Accounting and Reporting Policies	6 Months Ended
Jun. 30, 2017
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 2016 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 May 2014, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") No. 2014-09, Revenue from Contracts with Customers (Topic 606), which creates Topic 606 and supersedes Topic 605, Revenue Recognition. In August 2015, FASB issued ASU No. 2015-14, Revenue from Contracts with Customers (Topic 606), which postponed the effective date of 2014-09. Multiple ASUs and interpretative guidance have been issued in connection with ASU 2014-09. The core principle of Topic 606 is that an entity recognizes revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In general, the new guidance requires companies to use more judgment and make more estimates than under current guidance, including identifying performance obligations in the contract, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation. The standard is effective for public entities for interim and annual periods beginning after December 15, 2017; early adoption is not permitted. For financial reporting purposes, the standard allows for either full retrospective adoption, meaning the standard is applied to all of the periods presented, or modified retrospective adoption, meaning the standard is applied only to the most current period presented in the financial statements with the cumulative effect of initially applying the standard recognized at the date of initial application. The Company has begun their process to implement this new standard by reviewing all revenue sources to determine the sources that are in scope for this guidance. As a bank, key revenue sources, such as interest income have been identified as out of scope of this new guidance. The Company has not yet determined the financial statement impact this guidance will have. 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. The Company expects this ASU to impact its consolidated income and other comprehensive income disclosures for the fair value of its mutual fund investment and junior subordinated debenture. 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. Although an estimate of the impact of the new leasing standard has not yet been determined, the Company expects a significant new lease asset and related lease liability on the balance sheet due to the number of leased branches and standalone ATM sites the Bank currently has that are accounted for under current operating lease guidance. 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. The Company has established a project team for the implementation of this new standard. The team has started by working with a vendor to put a new Allowance for Loan Loss software in place and is collecting additional historical data to estimate the impact of this standard. An estimate of the impact of this standard has not yet been determined, however, the impact is expected to be significant. As of January 1, 2017, the Company adopted the Financial Accounting Standards Board's (FASB) Accounting Standard Update ("ASU") No. 2016-09, Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting. ASU 2016-09, seeks to simplify several aspects of the accounting for employee share-based payment transactions, including income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. As required by ASU 2016-09, all adjustments are reflected as of the beginning of the fiscal year, January 1, 2016. By applying this ASU, the Company no longer adjusts common stock for the tax impact of shares released, instead the tax impact is recognized as tax expense in the period the shares are released. This simplifies the tracking of the excess tax benefits and deficiencies, but could cause volatility in tax expense for the periods presented. The statement of cash flows has been adjusted to reflect the provisions of this ASU. The application of this ASU did not have a material impact on the financial statements. In January 2017, FASB issued ASU 2017-04, Intangibles - Goodwill and Other (Topic 350). The FASB is issuing this Update to eliminate the requirement to calculate the implied fair value of goodwill to measure a goodwill impairment charge. Instead, entities will record an impairment charge based on the excess of a reporting unit's carrying amount over its fair value. This ASU will be effective for public business entities for annual periods beginning after December 15, 2019 (i.e. calendar periods beginning on January 1, 2020, and interim periods therein. The Company does not expect any impact on the Company's consolidated financial statements resulting from the adoption of this update. In March 2017, FASB issued ASU 2017-08 - Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt Securities. The provisions of the update require premiums recognized upon the purchase of callable debt securities to be amortized to the earliest call date in order to avoid losses recognized upon call. For public business entities that are SEC filers the amendments of the update will become effective in fiscal years beginning after December 15, 2018. The Company does not expect the requirements of this update to have a material impact on the Company’s financial position, results of operations or cash flows.

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 2016 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 May 2014, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") No. 2014-09, Revenue from Contracts with Customers (Topic 606), which creates Topic 606 and supersedes Topic 605, Revenue Recognition. In August 2015, FASB issued ASU No. 2015-14, Revenue from Contracts with Customers (Topic 606), which postponed the effective date of 2014-09. Multiple ASUs and interpretative guidance have been issued in connection with ASU 2014-09. The core principle of Topic 606 is that an entity recognizes revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In general, the new guidance requires companies to use more judgment and make more estimates than under current guidance, including identifying performance obligations in the contract, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation. The standard is effective for public entities for interim and annual periods beginning after December 15, 2017; early adoption is not permitted. For financial reporting purposes, the standard allows for either full retrospective adoption, meaning the standard is applied to all of the periods presented, or modified retrospective adoption, meaning the standard is applied only to the most current period presented in the financial statements with the cumulative effect of initially applying the standard recognized at the date of initial application. The Company has begun their process to implement this new standard by reviewing all revenue sources to determine the sources that are in scope for this guidance. As a bank, key revenue sources, such as interest income have been identified as out of scope of this new guidance. The Company has not yet determined the financial statement impact this guidance will have.

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. The Company expects this ASU to impact its consolidated income and other comprehensive income disclosures for the fair value of its mutual fund investment and junior subordinated debenture.

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. Although an estimate of the impact of the new leasing standard has not yet been determined, the Company expects a significant new lease asset and related lease liability on the balance sheet due to the number of leased branches and standalone ATM sites the Bank currently has that are accounted for under current operating lease guidance.

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. The Company has established a project team for the implementation of this new standard. The team has started by working with a vendor to put a new Allowance for Loan Loss software in place and is collecting additional historical data to estimate the impact of this standard. An estimate of the impact of this standard has not yet been determined, however, the impact is expected to be significant.

As of January 1, 2017, the Company adopted the Financial Accounting Standards Board's (FASB) Accounting Standard Update ("ASU") No. 2016-09, Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting. ASU 2016-09, seeks to simplify several aspects of the accounting for employee share-based payment transactions, including income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. As required by ASU 2016-09, all adjustments are reflected as of the beginning of the fiscal year, January 1, 2016. By applying this ASU, the Company no longer adjusts common stock for the tax impact of shares released, instead the tax impact is recognized as tax expense in the period the shares are released. This simplifies the tracking of the excess tax benefits and deficiencies, but could cause volatility in tax expense for the periods presented. The statement of cash flows has been adjusted to reflect the provisions of this ASU. The application of this ASU did not have a material impact on the financial statements.

In January 2017, FASB issued ASU 2017-04, Intangibles - Goodwill and Other (Topic 350). The FASB is issuing this Update to eliminate the requirement to calculate the implied fair value of goodwill to measure a goodwill impairment charge. Instead, entities will record an impairment charge based on the excess of a reporting unit's carrying amount over its fair value. This ASU will be effective for public business entities for annual periods beginning after December 15, 2019 (i.e. calendar periods beginning on January 1, 2020, and interim periods therein. The Company does not expect any impact on the Company's consolidated financial statements resulting from the adoption of this update.

In March 2017, FASB issued ASU 2017-08 - Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt Securities. The provisions of the update require premiums recognized upon the purchase of callable debt securities to be amortized to the earliest call date in order to avoid losses recognized upon call. For public business entities that are SEC filers the amendments of the update will become effective in fiscal years beginning after December 15, 2018. The Company does not expect the requirements of this update to have a material impact on the Company’s financial position, results of operations or cash flows.