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

This element represents the amount of any measurement period adjustment (As defined) Realized during the reporting period to purchased performing loans acquired in connection with a business combination for which the initial accounting was incomplete.

No definition available.

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

This element represents the amount of any measurement period adjustment (As defined) Realized during the reporting period to total purchased loans acquired in connection with a business combination for which the initial accounting was incomplete.

No definition available.

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

The amount of total purchased loans in a business combination.

No definition available.

Name:	fusb_BusinessCombinationTotalPurchasedLoans
Namespace Prefix:	fusb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Fair value of acquired receivable from business combination, excluding certain loans and debt securities acquired in transfer.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=84161108&loc=d3e4845-128472

Name:	us-gaap_BusinessCombinationAcquiredReceivablesFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

The recorded balance, net of any applicable reductions (for example, unamortized accretable yield and allowance for loan losses). This relates to loans not accounted for debt securities with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=82894903&loc=d3e15032-111544

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 15
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82894507&loc=d3e13503-111538