Note 6 - Other Real Estate Owned and Repossessions (Details Textual) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Foreclosed Real Estate Owned, Fair Value Less Disposal Costs	$ 200	$ 600
Mortgage Loans in Process of Foreclosure, Amount	0	27
Repossessed Assets, Total	$ 200	$ 200

The fair value less estimated costs to sell of foreclosed residential real estate held by the Company as of the balance sheet date.

No definition available.

+ Details

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

- Definition

Carrying amount as of the balance sheet date of all assets obtained in full or partial satisfaction of a debt arrangement through foreclosure proceedings or defeasance; includes real and personal property; equity interests in corporations, partnerships, and joint ventures; and beneficial interests in trusts.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5162-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4437-111522

+ Details

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

- Definition

Recorded investment of consumer mortgage loan receivables secured by residential real estate properties for which formal foreclosure proceedings are in process.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 35
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL49126937-111524

+ Details

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