XML 124 R112.htm IDEA: XBRL DOCUMENT
v3.20.4

Fair Value of Financial Instruments - Assets and Liabilities Measured at Fair Value Using Significant Unobservable Inputs (Level 3) (Details) - Fair Value, Inputs, Level 3 [Member] $ in Thousands | Dec. 31, 2020 USD ($) | Dec. 31, 2019
--- | --- | ---
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Impaired loans | $ 28 |
OREO and other assets held-for-sale | $ 949 |
Weighted Average [Member] | Measurement Input, Comparability Adjustment |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Impaired loans |  | 0.095
OREO and other assets held-for-sale |  | (9.5)

X
- Definition Fair value portion of impaired loans by an entity as a result of past transactions or events. + References No definition available. + Details
Name: | fusb_ImpairedLoansFairValue
Namespace Prefix: | fusb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Value of input used to measure impaired loans. + References No definition available. + Details
Name: | fusb_ImpairedLoansMeasurementInput
Namespace Prefix: | fusb_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

X
- Definition Other real estate and other assets held-for-sale. + References No definition available. + Details
Name: | fusb_OtherRealEstateOtherAssetsFairValueDisclosure
Namespace Prefix: | fusb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Other real estate other assets measurement input. + References No definition available. + Details
Name: | fusb_OtherRealEstateOtherAssetsMeasurementInput
Namespace Prefix: | fusb_
Data Type: | xbrli:decimalItemType
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_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_WeightedAverageMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputComparabilityAdjustmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |