Name:	ubfo_InterestBearingDepositBrokered
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Time Deposits, $250,000 or More

No definition available.

Name:	ubfo_TimeDeposits250000orMore
Namespace Prefix:	ubfo_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Time Deposits, Less Than $250,000

No definition available.

Name:	ubfo_TimeDepositsLessThan250000
Namespace Prefix:	ubfo_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

The aggregate of all deposit liabilities held by the entity, including foreign and domestic, interest and noninterest bearing; may include demand deposits, saving deposits, Negotiable Order of Withdrawal (NOW) and time deposits among others.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.12)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Name:	us-gaap_Deposits
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

Name:	us-gaap_DepositsAbstract
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Amount of deposits in accounts that offer many of the same services as checking accounts although transactions may be somewhat more limited, share some of the characteristics of a money market fund and are insured by the Federal government, also known as money market accounts. Also includes amount of deposits in interest-bearing transaction accounts at banks or savings and loans, that are restricted in regard to ownership and can usually only be held by individuals, nonprofit entities and governments. Negotiable order of withdrawal accounts differ from money market demand accounts as they typically have higher reserve requirements and no limit on the number of checks that can be written.

No definition available.

Name:	us-gaap_DepositsMoneyMarketDepositsAndNegotiableOrderOfWithdrawalNOW
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of interest bearing deposits with no stated maturity, which may include passbook and statement savings accounts and money-market deposit accounts (MMDAs).

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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

The aggregate of all domestic and foreign interest-bearing deposit liabilities.

Name:	us-gaap_InterestBearingDepositLiabilities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

Name:	us-gaap_InterestBearingDepositLiabilitiesAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
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Period Type:	duration

The aggregate amount of all domestic and foreign noninterest-bearing deposits liabilities held by the entity.