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v3.21.2

Leases - Narrative (Details) | 9 Months Ended
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Sep. 30, 2021 contract
Leases [Abstract] |
Operating lease, number of contracts | 12
Financing lease, number of contracts | 0

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- Definition Lessee, Financing Lease, Number Of Contracts + References No definition available. + Details
Name: | ubfo_LesseeFinancingLeaseNumberOfContracts
Namespace Prefix: | ubfo_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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- Definition Lessee, Operating Lease, Number Of Contracts + References No definition available. + Details
Name: | ubfo_LesseeOperatingLeaseNumberOfContracts
Namespace Prefix: | ubfo_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_LeasesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration