XML 62 R55.htm IDEA: XBRL DOCUMENT v3.25.1

Loans And Leases - Schedule of Amortized Cost Basis of Collateral Dependent Loans (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2025	Dec. 31, 2024
Total loans individually evaluated	$ 6,895	$ 7,601
Real Estate [Member] | Construction, Land Development and Other Land Loans [Member]
Total loans individually evaluated	2,464	2,489
Real Estate [Member] | Secured by Real Estate 1-4 Family Residential Properties [Member]
Total loans individually evaluated	1,367	1,402
Real Estate [Member] | Secured by Non-residential Commercial Real Estate [Member]
Total loans individually evaluated	371	383
Commercial And Industrial Loans [Member]
Total loans individually evaluated	2,693	3,327
Real Estate [Member]
Total loans individually evaluated	4,202	4,274
Real Estate [Member] | Real Estate [Member] | Construction, Land Development and Other Land Loans [Member]
Total loans individually evaluated	2,464	2,489
Real Estate [Member] | Real Estate [Member] | Secured by Real Estate 1-4 Family Residential Properties [Member]
Total loans individually evaluated	1,367	1,402
Real Estate [Member] | Real Estate [Member] | Secured by Non-residential Commercial Real Estate [Member]
Total loans individually evaluated	371	383
Other [Member]
Total loans individually evaluated	2,693	3,327
Other [Member] | Commercial And Industrial Loans [Member]
Total loans individually evaluated	$ 2,693	$ 3,327

X

- Definition

Collateral Loans Individually Evaluated Amortized Cost Basis

+ References

No definition available.

+ Details

Name:	fusb_CollateralLoansIndividuallyEvaluatedAmortizedCostBasis
Namespace Prefix:	fusb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=fusb_RealEstate1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fusb_ConstructionLandDevelopmentAndOtherLandLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fusb_SecuredByRealEstate1To4FamilyResidentialPropertiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fusb_SecuredByNonResidentialCommercialRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=fusb_CommercialAndIndustrialLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_CollateralAxis=us-gaap_RealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_CollateralAxis=fusb_OtherMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: