XML 65 R56.htm IDEA: XBRL DOCUMENT v3.25.0.1

Description Of Business - Additional Information (Details) - Segment	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of states	17
Number of reportable segments	1	2

X

- Definition

Number of states conducting lending of loan portfolio.

+ References

No definition available.

+ Details

Name:	fusb_NumberOfStates
Namespace Prefix:	fusb_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Organization consolidation and presentation of financial statements.

+ References

No definition available.

+ Details

Name:	fusb_OrganizationConsolidationAndPresentationOfFinancialStatementsLineItems
Namespace Prefix:	fusb_
Data Type:	xbrli:stringItemType
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/2003/role/exampleRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 47
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482785/280-10-55-47

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 54
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482785/280-10-55-54

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-18

+ Details

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