XML 24 R72.htm IDEA: XBRL DOCUMENT
v3.20.1

Derivative Financial Instruments - Additional Information (Details) - USD ($) | Oct. 01, 2019 | Aug. 21, 2019 | Aug. 09, 2019 | Jul. 22, 2019 | Jul. 08, 2019 | Mar. 31, 2020
--- | --- | --- | --- | --- | --- | ---
Forward Interest Rate Swap Contract One [Member] |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |
Notional amount, total |  |  |  |  | $ 10,000,000 |
Derivative term of contract |  |  |  |  | 7 years |
Derivative, fixed interest rate |  |  |  |  | 1.79% |
Forward Interest Rate Swap Contract One [Member] | Minimum [Member] |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |
Expected derivative notional amount for next seven years |  |  |  |  |  | $ 10,000,000
Forward Interest Rate Swap Contract Two [Member] |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |
Notional amount, total |  |  |  | $ 10,000,000 |  |
Derivative term of contract |  |  |  | 5 years |  |
Derivative, fixed interest rate |  |  |  | 1.698% |  |
Forward Interest Rate Swap Contract Two [Member] | Minimum [Member] |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |
Expected derivative notional amount for next five years |  |  |  | $ 10,000 |  |
Forward Interest Rate Swap Contract Five [Member] |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |
Notional amount, total | $ 10,000,000 |  |  |  |  |
Derivative term of contract | 5 years |  |  |  |  |
Derivative, fixed interest rate | 1.357% |  |  |  |  |
Forward Interest Rate Swap Contract Three [Member] |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |
Notional amount, total |  |  | $ 10,000,000 |  |  |
Derivative term of contract |  |  | 5 years |  |  |
Derivative, fixed interest rate |  |  | 1.406% |  |  |
Forward Interest Rate Swap Contract Four [Member] |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |
Notional amount, total |  | $ 10,000,000 |  |  |  |
Derivative term of contract |  | 5 years |  |  |  |
Derivative, fixed interest rate |  | 1.292% |  |  |  |

X
- Definition Expected derivative notional amount for next five years. + References No definition available. + Details
Name: | fusb_ExpectedDerivativeNotionalAmountForNextFiveYears
Namespace Prefix: | fusb_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | instant

X
- Definition Expected derivative notional amount for next seven years. + References No definition available. + Details
Name: | fusb_ExpectedDerivativeNotionalAmountForNextSevenYears
Namespace Prefix: | fusb_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | instant

X
- Definition Nominal or face amount used to calculate payments on the derivative asset. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1A -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5579245-113959 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1B -URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5580258-113959 Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5579245-113959 + Details
Name: | us-gaap_DerivativeAssetNotionalAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | instant

X
- Definition Fixed interest rate related to the interest rate derivative. + References No definition available. + Details
Name: | us-gaap_DerivativeFixedInterestRate
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
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_DerivativeLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Period the derivative contract is outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
Name: | us-gaap_DerivativeTermOfContract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=fusb_ForwardInterestRateSwapContractOneMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=fusb_ForwardInterestRateSwapContractTwoMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=fusb_ForwardInterestRateSwapContractFiveMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=fusb_ForwardInterestRateSwapContractThreeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=fusb_ForwardInterestRateSwapContractFourMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |