XML 118 R106.htm IDEA: XBRL DOCUMENT v3.22.4

Segment Reporting - Additional Information (Details)		3 Months Ended	12 Months Ended
	Sep. 03, 2021 Branch	Sep. 30, 2021 Branch	Dec. 31, 2022 Segment
Segment Reporting Information [Line Items]
Number of reportable segments | Segment			2
ALC [Member]
Segment Reporting Information [Line Items]
Number of office closed | Branch	20	20

X

- Definition

Represents number of office closed during period for restructuring and related cost.

+ References

No definition available.

+ Details

Name:	fusb_RestructuringAndRelatedCostNumberOfOfficeClosed
Namespace Prefix:	fusb_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 18
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8672-108599

+ Details

Name:	us-gaap_NumberOfReportableSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_SegmentReportingInformationLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_RestructuringCostAndReserveAxis=fusb_AcceptanceLoanCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: