    <SEC-DOCUMENT>0001137547-25-000130-index.html : 20251217
    <SEC-HEADER>0001137547-25-000130.hdr.sgml : 20251217
    <ACCEPTANCE-DATETIME>20251217084613
    ACCESSION NUMBER:		0001137547-25-000130
    CONFORMED SUBMISSION TYPE:	8-K
    PUBLIC DOCUMENT COUNT:		59
    CONFORMED PERIOD OF REPORT:	20251216
    ITEM INFORMATION:		Entry into a Material Definitive Agreement
    ITEM INFORMATION:		Regulation FD Disclosure
    ITEM INFORMATION:		Financial Statements and Exhibits
    FILED AS OF DATE:		20251217
    DATE AS OF CHANGE:		20251217

    FILER:

    	COMPANY DATA:
    		COMPANY CONFORMED NAME:			UNITED SECURITY BANCSHARES
    		CENTRAL INDEX KEY:			0001137547
    		STANDARD INDUSTRIAL CLASSIFICATION:	NATIONAL COMMERCIAL BANKS [6021]
    		ORGANIZATION NAME:           	02 Finance
    		EIN:				912112732
    		STATE OF INCORPORATION:			CA
    		FISCAL YEAR END:			1231

    	FILING VALUES:
    		FORM TYPE:		8-K
    		SEC ACT:		1934 Act
    		SEC FILE NUMBER:	000-32897
    		FILM NUMBER:		251577349

    	BUSINESS ADDRESS:
    		STREET 1:		2126 INYO STREET
    		CITY:			FRESNO
    		STATE:			CA
    		ZIP:			93721
    		BUSINESS PHONE:		5594906261

    	MAIL ADDRESS:
    		STREET 1:		2126 INYO STREET
    		CITY:			FRESNO
    		STATE:			CA
    		ZIP:			93721
    </SEC-HEADER>
    <DOCUMENT>
    <TYPE>8-K
    <SEQUENCE>1
    <FILENAME>ubfo-20251216.htm
    <DESCRIPTION>8-K
    <TEXT>
    Document 1 - file: ubfo-20251216.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-2.1
    <SEQUENCE>2
    <FILENAME>projectutopia-agreementand.htm
    <DESCRIPTION>EX-2.1
    <TEXT>
    Document 2 - file: projectutopia-agreementand.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-10.1
    <SEQUENCE>3
    <FILENAME>projectutopia-votingands.htm
    <DESCRIPTION>EX-10.1
    <TEXT>
    Document 3 - file: projectutopia-votingands.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-10.2
    <SEQUENCE>4
    <FILENAME>projectutopia-acquirorvo.htm
    <DESCRIPTION>EX-10.2
    <TEXT>
    Document 4 - file: projectutopia-acquirorvo.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-99.1
    <SEQUENCE>5
    <FILENAME>communitywestbancsharesand.htm
    <DESCRIPTION>EX-99.1
    <TEXT>
    Document 5 - file: communitywestbancsharesand.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-99.2
    <SEQUENCE>6
    <FILENAME>projectutopiainvestorpre.htm
    <DESCRIPTION>EX-99.2
    <TEXT>
    Document 6 - file: projectutopiainvestorpre.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-101.SCH
    <SEQUENCE>7
    <FILENAME>ubfo-20251216.xsd
    <DESCRIPTION>XBRL TAXONOMY EXTENSION SCHEMA DOCUMENT
    <TEXT>
    Document 7 - file: ubfo-20251216.xsd

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-101.LAB
    <SEQUENCE>8
    <FILENAME>ubfo-20251216_lab.xml
    <DESCRIPTION>XBRL TAXONOMY EXTENSION LABEL LINKBASE DOCUMENT
    <TEXT>
    Document 8 - file: ubfo-20251216_lab.xml

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-101.PRE
    <SEQUENCE>9
    <FILENAME>ubfo-20251216_pre.xml
    <DESCRIPTION>XBRL TAXONOMY EXTENSION PRESENTATION LINKBASE DOCUMENT
    <TEXT>
    Document 9 - file: ubfo-20251216_pre.xml

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>10
    <FILENAME>image_0a.jpg
    <TEXT>
    Document 10 - file: image_0a.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>11
    <FILENAME>image_1a.jpg
    <TEXT>
    Document 11 - file: image_1a.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>12
    <FILENAME>image_2a.jpg
    <TEXT>
    Document 12 - file: image_2a.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>13
    <FILENAME>projectutopia-acquirorvo001.jpg
    <TEXT>
    Document 13 - file: projectutopia-acquirorvo001.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>14
    <FILENAME>projectutopia-acquirorvo002.jpg
    <TEXT>
    Document 14 - file: projectutopia-acquirorvo002.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>15
    <FILENAME>projectutopia-acquirorvo003.jpg
    <TEXT>
    Document 15 - file: projectutopia-acquirorvo003.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>16
    <FILENAME>projectutopia-acquirorvo004.jpg
    <TEXT>
    Document 16 - file: projectutopia-acquirorvo004.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>17
    <FILENAME>projectutopia-acquirorvo005.jpg
    <TEXT>
    Document 17 - file: projectutopia-acquirorvo005.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>18
    <FILENAME>projectutopia-acquirorvo006.jpg
    <TEXT>
    Document 18 - file: projectutopia-acquirorvo006.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>19
    <FILENAME>projectutopia-acquirorvo007.jpg
    <TEXT>
    Document 19 - file: projectutopia-acquirorvo007.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>20
    <FILENAME>projectutopia-acquirorvo008.jpg
    <TEXT>
    Document 20 - file: projectutopia-acquirorvo008.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>21
    <FILENAME>projectutopia-votingands001.jpg
    <TEXT>
    Document 21 - file: projectutopia-votingands001.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>22
    <FILENAME>projectutopia-votingands002.jpg
    <TEXT>
    Document 22 - file: projectutopia-votingands002.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>23
    <FILENAME>projectutopia-votingands003.jpg
    <TEXT>
    Document 23 - file: projectutopia-votingands003.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>24
    <FILENAME>projectutopia-votingands004.jpg
    <TEXT>
    Document 24 - file: projectutopia-votingands004.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>25
    <FILENAME>projectutopia-votingands005.jpg
    <TEXT>
    Document 25 - file: projectutopia-votingands005.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>26
    <FILENAME>projectutopia-votingands006.jpg
    <TEXT>
    Document 26 - file: projectutopia-votingands006.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>27
    <FILENAME>projectutopia-votingands007.jpg
    <TEXT>
    Document 27 - file: projectutopia-votingands007.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>28
    <FILENAME>projectutopia-votingands008.jpg
    <TEXT>
    Document 28 - file: projectutopia-votingands008.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>29
    <FILENAME>projectutopia-votingands009.jpg
    <TEXT>
    Document 29 - file: projectutopia-votingands009.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>30
    <FILENAME>projectutopia-votingands010.jpg
    <TEXT>
    Document 30 - file: projectutopia-votingands010.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>31
    <FILENAME>projectutopiainvestorpre001.jpg
    <TEXT>
    Document 31 - file: projectutopiainvestorpre001.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>32
    <FILENAME>projectutopiainvestorpre002.jpg
    <TEXT>
    Document 32 - file: projectutopiainvestorpre002.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>33
    <FILENAME>projectutopiainvestorpre003.jpg
    <TEXT>
    Document 33 - file: projectutopiainvestorpre003.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>34
    <FILENAME>projectutopiainvestorpre004.jpg
    <TEXT>
    Document 34 - file: projectutopiainvestorpre004.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>35
    <FILENAME>projectutopiainvestorpre005.jpg
    <TEXT>
    Document 35 - file: projectutopiainvestorpre005.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>36
    <FILENAME>projectutopiainvestorpre006.jpg
    <TEXT>
    Document 36 - file: projectutopiainvestorpre006.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>37
    <FILENAME>projectutopiainvestorpre007.jpg
    <TEXT>
    Document 37 - file: projectutopiainvestorpre007.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>38
    <FILENAME>projectutopiainvestorpre008.jpg
    <TEXT>
    Document 38 - file: projectutopiainvestorpre008.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>39
    <FILENAME>projectutopiainvestorpre009.jpg
    <TEXT>
    Document 39 - file: projectutopiainvestorpre009.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>40
    <FILENAME>projectutopiainvestorpre010.jpg
    <TEXT>
    Document 40 - file: projectutopiainvestorpre010.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>41
    <FILENAME>projectutopiainvestorpre011.jpg
    <TEXT>
    Document 41 - file: projectutopiainvestorpre011.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>42
    <FILENAME>projectutopiainvestorpre012.jpg
    <TEXT>
    Document 42 - file: projectutopiainvestorpre012.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>43
    <FILENAME>projectutopiainvestorpre013.jpg
    <TEXT>
    Document 43 - file: projectutopiainvestorpre013.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>44
    <FILENAME>projectutopiainvestorpre014.jpg
    <TEXT>
    Document 44 - file: projectutopiainvestorpre014.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>45
    <FILENAME>projectutopiainvestorpre015.jpg
    <TEXT>
    Document 45 - file: projectutopiainvestorpre015.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>46
    <FILENAME>projectutopiainvestorpre016.jpg
    <TEXT>
    Document 46 - file: projectutopiainvestorpre016.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>47
    <FILENAME>projectutopiainvestorpre017.jpg
    <TEXT>
    Document 47 - file: projectutopiainvestorpre017.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>48
    <FILENAME>projectutopiainvestorpre018.jpg
    <TEXT>
    Document 48 - file: projectutopiainvestorpre018.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>49
    <FILENAME>projectutopiainvestorpre019.jpg
    <TEXT>
    Document 49 - file: projectutopiainvestorpre019.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>50
    <FILENAME>projectutopiainvestorpre020.jpg
    <TEXT>
    Document 50 - file: projectutopiainvestorpre020.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>51
    <FILENAME>projectutopiainvestorpre021.jpg
    <TEXT>
    Document 51 - file: projectutopiainvestorpre021.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>XML
    <SEQUENCE>53
    <FILENAME>R1.htm
    <DESCRIPTION>IDEA: XBRL DOCUMENT
    <TEXT>
    Document 53 - file: R1.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>XML
    <SEQUENCE>54
    <FILENAME>Show.js
    <DESCRIPTION>IDEA: XBRL DOCUMENT
    <TEXT>
    Document 54 - file: Show.js

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>XML
    <SEQUENCE>55
    <FILENAME>report.css
    <DESCRIPTION>IDEA: XBRL DOCUMENT
    <TEXT>
    Document 55 - file: report.css

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>XML
    <SEQUENCE>57
    <FILENAME>FilingSummary.xml
    <DESCRIPTION>IDEA: XBRL DOCUMENT
    <TEXT>
    Document 57 - file: FilingSummary.html

    Document 57 - RAW XML: FilingSummary.xml

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>JSON
    <SEQUENCE>59
    <FILENAME>MetaLinks.json
    <DESCRIPTION>IDEA: XBRL DOCUMENT
    <TEXT>
    Document 59 - file: MetaLinks.json

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>ZIP
    <SEQUENCE>60
    <FILENAME>0001137547-25-000130-xbrl.zip
    <DESCRIPTION>IDEA: XBRL DOCUMENT
    <TEXT>
    Document 60 - file: 0001137547-25-000130-xbrl.zip

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>XML
    <SEQUENCE>61
    <FILENAME>ubfo-20251216_htm.xml
    <DESCRIPTION>IDEA: XBRL DOCUMENT
    <TEXT>
    Document 61 - file: ubfo-20251216_htm.html

    Document 61 - RAW XML: ubfo-20251216_htm.xml

    </DOCUMENT>
    </SEC-DOCUMENT>