XML 109 R100.htm IDEA: XBRL DOCUMENT v3.25.0.1

Derivative Financial Instruments - Schedule of Notional Amount and Fair Value of Derivative Instruments Included on Company's Consolidated Balance Sheets on a net Basis (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2024	Dec. 31, 2023	Feb. 28, 2023	May 31, 2022
Derivatives Designated as Hedging Instruments [Member]
Derivatives Fair Value [Line Items]
Notional Amount				$ 40,000
Estimated Fair Value Gain (Loss)	[1]	$ 678	$ (119)
Derivatives Designated as Hedging Instruments [Member] | Fair Value Hedging [Member]
Derivatives Fair Value [Line Items]
Estimated Fair Value Gain (Loss)	[1]	69	(119)
Derivatives Designated as Hedging Instruments [Member] | Fair Value Hedging [Member] | Interest Rate Swaps Related To Fixed Rate Indirect Consumer Loans [Member]
Derivatives Fair Value [Line Items]
Notional Amount		30,000	30,000
Estimated Fair Value Gain (Loss)	[1]	69	$ (119)
Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedging [Member]
Derivatives Fair Value [Line Items]
Notional Amount				$ 10,000	$ 10,000
Estimated Fair Value Gain (Loss)	[1]	609
Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedging [Member] | Interest Rate Swaps Related to Interest-Bearing Liabilities [Member]
Derivatives Fair Value [Line Items]
Notional Amount		40,000
Estimated Fair Value Gain (Loss)	[1]	609
Derivatives Not Designated as Hedging Instruments [Member]
Derivatives Fair Value [Line Items]
Estimated Fair Value Gain (Loss)	[1]	(36)
Derivatives Not Designated as Hedging Instruments [Member] | Interest Rate Floors [Member]
Derivatives Fair Value [Line Items]
Estimated Fair Value Gain (Loss)	[1]	18
Derivatives Not Designated as Hedging Instruments [Member] | Credit Risk Participation Agreements [Member]
Derivatives Fair Value [Line Items]
Estimated Fair Value Gain (Loss)	[1]	(54)
Derivatives Not Designated as Hedging Instruments [Member] | Fair Value Hedging [Member] | Interest Rate Floors [Member]
Derivatives Fair Value [Line Items]
Notional Amount		50,000
Derivatives Not Designated as Hedging Instruments [Member] | Fair Value Hedging [Member] | Credit Risk Participation Agreements [Member]
Derivatives Fair Value [Line Items]
Notional Amount		$ 15,198
[1] Derivatives in a gain position are recorded as other assets and derivatives in a loss position are recorded as other liabilities in the consolidated balance sheets.

X

- Definition

Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4A
-Subparagraph (b)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-4A

+ Details

Name:	us-gaap_DerivativeGainLossOnDerivativeNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Nominal or face amount used to calculate payment on derivative.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-1B

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1A
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-1A

+ Details

Name:	us-gaap_DerivativeNotionalAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

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

X

- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_DesignatedAsHedgingInstrumentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=us-gaap_FairValueHedgingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=fusb_InterestRateSwapsRelatedToFixedRateIndirectConsumerLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=us-gaap_CashFlowHedgingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=fusb_InterestRateSwapsRelatedToInterestBearingLiabilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_NondesignatedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=fusb_InterestRateFloorsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=fusb_CreditRiskParticipationAgreementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: