XML 117 R105.htm IDEA: XBRL DOCUMENT
v3.22.4

Derivative Financial Instruments - Schedule of Hedging Derivative Instruments' Effect on Company's Consolidated Statement of Operations (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2022 | Dec. 31, 2021
Interest and Fees on Loans [Member] |  |
Derivative Instruments Gain Loss [Line Items] |  |
Interest income (expense) | $ 75 | $ (253)
Interest on Deposits [Member] |  |
Derivative Instruments Gain Loss [Line Items] |  |
Interest income (expense) | 56 | (127)
Interest on Short-Term Borrowings [Member] |  |
Derivative Instruments Gain Loss [Line Items] |  |
Interest income (expense) | (5) | (333)
Net Increase (Decrease) to Income Before Income Taxes [Member] |  |
Derivative Instruments Gain Loss [Line Items] |  |
Interest income (expense) | $ 126 | $ (713)

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

X
- Definition The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4D -Subparagraph (b) -URI https://asc.fasb.org/extlink&oid=125515794&loc=SL5624177-113959 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (c) -URI https://asc.fasb.org/extlink&oid=125515794&loc=SL5624171-113959 + Details
Name: | us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | us-gaap_IncomeStatementLocationAxis=fusb_InterestAndFeesOnLoansMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_IncomeStatementLocationAxis=fusb_InterestOnDepositsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_IncomeStatementLocationAxis=fusb_InterestOnShortTermBorrowingsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_IncomeStatementLocationAxis=fusb_NetIncreaseDecreaseToIncomeBeforeIncomeTaxesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |