Organization and Summary of Significant Accounting and Reporting Policies	9 Months Ended
Sep. 30, 2019
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 (Company or USB) and its wholly owned subsidiary United Security Bank (Bank). Intercompany accounts and transactions have been eliminated in consolidation. These unaudited financial statements have been prepared in accordance with accounting principles generally accepted in the United States (GAAP) for interim financial information on a basis consistent with the accounting policies reflected in the audited consolidated financial statements of the Company included in its 2018 Annual Report on Form 10-K. These interim consolidated financial statements do not include all of the information and footnotes required by GAAP 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. Reclassifications: Certain reclassifications have been made to prior year financial statements to conform to the classifications used in 2019. None of the reclassifications impacted equity or net income. Revenue from Contracts with Customers: The Company records revenue from contracts with customers in accordance with Accounting Standards Codification Topic 606, “Revenue from Contracts with Customers” (Topic 606). Under Topic 606, the Company must identify the contract with a customer, identify the performance obligations in the contract, determine the transaction price, allocate the transaction price to the performance obligations in the contract, and recognize revenue when (or as) the Company satisfies a performance obligation. The Company’s primary sources of revenue are derived from interest and dividends earned on loans, investment securities, and other financial instruments that are not within the scope of Topic 606. The Company has evaluated the nature of its contracts with customers and determined that further disaggregation of revenue from contracts with customers into more granular categories beyond what is presented in the Consolidated Statements of Income was not necessary. The Company generally fully satisfies its performance obligations on its contracts with customers as services are rendered and the transaction prices are typically fixed; charged either on a periodic basis or based on activity. Because performance obligations are satisfied as services are rendered and the transaction prices are fixed, there is little judgment involved in applying Topic 606 that significantly affects the determination of the amount and timing of revenue from contracts with customers. The Company adopted Topic 606 using the modified retrospective method on all contracts not completed as of January 1, 2018. The adoption of Topic 606 did not result in a material change to the accounting for any of the in-scope revenue streams. As such, no cumulative effect adjustment was recorded. Leases: The Company determines if an arrangement is a lease at inception. Operating leases are included in other assets and other liabilities on the consolidated balance sheets. Finance leases, if necessary, are included in property and equipment, other current liabilities, and other long-term liabilities on the consolidated balance sheets. Operating lease ROU assets and operating lease liabilities are recognized based on the present value of the future minimum lease payments over the lease term at commencement date. As most of the leases do not provide an implicit rate, the Company uses its incremental borrowing rate based on the information available at commencement date in determining the present value of future payments. The operating lease ROU asset also includes any lease payments made and excludes lease incentives and initial direct costs incurred. The Company's lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. Lease expense for minimum lease payments is recognized on a straight-line basis over the lease term. Recently Adopted Accounting Standards: In February 2016, FASB issued ASU 2016-02, Leases (Topic 842). The FASB issued 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. The Company adopted the New Lease Standard as of January 1, 2019 using an optional transition method, as discussed in ASU 2018-11 below, that allows application of the new leases standard at the adoption date. Under the optional transition method, financial result reported in periods prior to 2019 are unchanged. The Company also elected the package of practical expedients, which among other things did not require assessment of lease classification. See Note 7 - Leases for additional information. In July 2018, FASB issued ASU 2018-11, Leases (Topic 842), Targeted Improvements, which amends ASC 842, Leases. The amendments in this Update allowed lessors to combine lease and associated nonlease components by class of underlying asset in contract that meet certain criteria. For a lessor to qualify for this practical expedient, the lease and related nonlease components must have the same timing and pattern of transfer, and the lease component, if accounted for on a stand-alone basis, would be classified as an operating lease. Additionally, the Update provided an optional method for adopting the new leasing guidance. The optional transition method allows entities to apply the new guidance at the adoption date by recognizing a cumulative-effect adjustment to the opening balance of the retained earnings, and not to restate the comparative periods presented. The Company has elected to use the practical expedient, and optional method of adoption as set-forth in this Update. See Note 7 - Leases for additional information. Recent Accounting Standards Not Yet Adopted: 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 original amendment was effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. In October 2019 FASB unanimously approved a vote to delay the effective date of this Standard to be effective for fiscal years beginning after December 15, 2022. The Company has formed a project team that is responsible for oversight of the Company’s implementation strategy for compliance with provisions of the new standard. An external provider specializing in community bank loss driver and CECL reserving model design as well as other related consulting services has been retained, and the Company continues to evaluate potential CECL modeling alternatives. As part of this process, the Company has determined potential loan pool segmentation and sub-segmentation under CECL, as well as evaluated the key economic loss drivers for each segment. The Company presently plans to generate and evaluate model scenarios under CECL in tandem with its current reserving processes for interim and annual reporting periods in 2020. While the Company is currently unable to reasonably estimate the impact of adopting this new guidance, management expects the impact of adoption will be significantly influenced by the composition and quality of the Company’s loans and investment securities as well as the economic conditions as of the date of adoption. The Company also anticipates significant changes to the processes and procedures for calculating the reserve for credit losses and continues to evaluate the potential impact on the Company's consolidated financial statements. Additionally, in regard to the recently approved delay in implementation, the Company is evaluating it's expected implementation date. 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 August 2018, FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework — Changes to the Disclosure Requirements for Fair Value Measurement. The amendments in this Update modify the disclosure requirements on fair value measurements in Topic 820, Fair Value Measurement, based on the concepts within FASB's Concepts Statement, including the consideration of costs and benefits. The amendment calls for the removal, modification, and addition of certain disclosure aspects to promote the appropriate exercise of discretion by entities when considering fair value measurement disclosures. The amendments of the update will become effective in fiscal years beginning after December 15, 2019. 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. In October 2018, FASB issued ASU 2018-16, Derivatives and Hedging (Topic 815): Inclusion of the Secured Overnight Financing Rate (SOFR) Overnight Index Swap (OIS) Rate as a Benchmark Interest Rate for Hedge Accounting Purposes. The amendments in this Update allow entities to designate a change in the benchmark interest rate utilized for fixed-rate financial instruments, from the previously utilized LIBOR rate. For public business entities amendments of the update will become effective in fiscal years beginning after December 15, 2019. The Company continues to review the potential impact resulting from such a change. As of September 30, 2019, the Company continues to utilize the LIBOR rate for fixed-rate financial instruments. 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 (Company or USB) and its wholly owned subsidiary United Security Bank (Bank). Intercompany accounts and transactions have been eliminated in consolidation.

These unaudited financial statements have been prepared in accordance with accounting principles generally accepted in the United States (GAAP) for interim financial information on a basis consistent with the accounting policies reflected in the audited consolidated financial statements of the Company included in its 2018 Annual Report on Form 10-K. These interim consolidated financial statements do not include all of the information and footnotes required by GAAP 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.

Reclassifications:

Certain reclassifications have been made to prior year financial statements to conform to the classifications used in 2019. None of the reclassifications impacted equity or net income.

Revenue from Contracts with Customers:

The Company records revenue from contracts with customers in accordance with Accounting Standards Codification Topic 606, “Revenue from Contracts with Customers” (Topic 606). Under Topic 606, the Company must identify the contract with a customer, identify the performance obligations in the contract, determine the transaction price, allocate the transaction price to the performance obligations in the contract, and recognize revenue when (or as) the Company satisfies a performance obligation.

The Company’s primary sources of revenue are derived from interest and dividends earned on loans, investment securities, and other financial instruments that are not within the scope of Topic 606. The Company has evaluated the nature of its contracts with customers and determined that further disaggregation of revenue from contracts with customers into more granular categories beyond what is presented in the Consolidated Statements of Income was not necessary. The Company generally fully satisfies its performance obligations on its contracts with customers as services are rendered and the transaction prices are typically fixed; charged either on a periodic basis or based on activity. Because performance obligations are satisfied as services are rendered and the transaction prices are fixed, there is little judgment involved in applying Topic 606 that significantly affects the determination of the amount and timing of revenue from contracts with customers. The Company adopted Topic 606 using the modified retrospective method on all contracts not completed as of January 1, 2018. The adoption of Topic 606 did not result in a material change to the accounting for any of the in-scope revenue streams. As such, no cumulative effect adjustment was recorded.

Leases:

The Company determines if an arrangement is a lease at inception. Operating leases are included in other assets and other liabilities on the consolidated balance sheets. Finance leases, if necessary, are included in property and equipment, other current liabilities, and other long-term liabilities on the consolidated balance sheets.

Operating lease ROU assets and operating lease liabilities are recognized based on the present value of the future minimum lease payments over the lease term at commencement date. As most of the leases do not provide an implicit rate, the Company uses its incremental borrowing rate based on the information available at commencement date in determining the present value of future payments. The operating lease ROU asset also includes any lease payments made and excludes lease incentives and initial direct costs incurred. The Company's lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. Lease expense for minimum lease payments is recognized on a straight-line basis over the lease term.

Recently Adopted Accounting Standards:

In February 2016, FASB issued ASU 2016-02, Leases (Topic 842). The FASB issued 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. The Company adopted the New Lease Standard as of January 1, 2019 using an optional transition method, as discussed in ASU 2018-11 below, that allows application of the new leases standard at the adoption date. Under the optional transition method, financial result reported in periods prior to 2019 are unchanged. The Company also elected the package of practical expedients, which among other things did not require assessment of lease classification. See Note 7 - Leases for additional information.

In July 2018, FASB issued ASU 2018-11, Leases (Topic 842), Targeted Improvements, which amends ASC 842, Leases. The amendments in this Update allowed lessors to combine lease and associated nonlease components by class of underlying asset in contract that meet certain criteria. For a lessor to qualify for this practical expedient, the lease and related nonlease components must have the same timing and pattern of transfer, and the lease component, if accounted for on a stand-alone basis, would be classified as an operating lease. Additionally, the Update provided an optional method for adopting the new leasing guidance. The optional transition method allows entities to apply the new guidance at the adoption date by recognizing a cumulative-effect adjustment to the opening balance of the retained earnings, and not to restate the comparative periods presented. The Company has elected to use the practical expedient, and optional method of adoption as set-forth in this Update. See Note 7 - Leases for additional information.

Recent Accounting Standards Not Yet Adopted:

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 original amendment was effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. In October 2019 FASB unanimously approved a vote to delay the effective date of this Standard to be effective for fiscal years beginning after December 15, 2022. The Company has formed a project team that is responsible for oversight of the Company’s implementation strategy for compliance with provisions of the new standard. An external provider specializing in community bank loss driver and CECL reserving model design as well as other related consulting services has been retained, and the Company continues to evaluate potential CECL modeling alternatives. As part of this process, the Company has determined potential loan pool segmentation and sub-segmentation under CECL, as well as evaluated the key economic loss drivers for each segment. The Company presently plans to generate and evaluate model scenarios under CECL in tandem with its current reserving processes for interim and annual reporting periods in 2020. While the Company is currently unable to reasonably estimate the impact of adopting this new guidance, management expects the impact of adoption will be significantly influenced by the composition and quality of the Company’s loans and investment securities as well as the economic conditions as of the date of adoption. The Company also anticipates significant changes to the processes and procedures for calculating the reserve for credit losses and continues to evaluate the potential impact on the Company's consolidated financial statements. Additionally, in regard to the recently approved delay in implementation, the Company is evaluating it's expected implementation date.

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 August 2018, FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework — Changes to the Disclosure Requirements for Fair Value Measurement. The amendments in this Update modify the disclosure requirements on fair value measurements in Topic 820, Fair Value Measurement, based on the concepts within FASB's Concepts Statement, including the consideration of costs and benefits. The amendment calls for the removal, modification, and addition of certain disclosure aspects to promote the appropriate exercise of discretion by entities when considering fair value measurement disclosures. The amendments of the update will become effective in fiscal years beginning after December 15, 2019. 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.

In October 2018, FASB issued ASU 2018-16, Derivatives and Hedging (Topic 815): Inclusion of the Secured Overnight Financing Rate (SOFR) Overnight Index Swap (OIS) Rate as a Benchmark Interest Rate for Hedge Accounting Purposes. The amendments in this Update allow entities to designate a change in the benchmark interest rate utilized for fixed-rate financial instruments, from the previously utilized LIBOR rate. For public business entities amendments of the update will become effective in fiscal years beginning after December 15, 2019. The Company continues to review the potential impact resulting from such a change. As of September 30, 2019, the Company continues to utilize the LIBOR rate for fixed-rate financial instruments. 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.