XML 62 R56.htm IDEA: XBRL DOCUMENT
v3.25.3

Other Real Estate Owned and Repossessed Assets - Summary of Foreclosed Property Activity (Details) - USD ($) $ in Thousands | 9 Months Ended
--- | ---
Sep. 30, 2025 | Sep. 30, 2024
Other Real Estate [Abstract] |  |  |
Beginning balance |  | $ 1,509 | $ 602
Additions | [1] | 0 | 26
Sales proceeds |  | (204) | 0
Gross gains |  | 53 | 0
Gross losses |  | 0 | 0
Net gains |  | 53 | 0
Impairment |  | (200) | (90)
Ending balance |  | $ 1,158 | $ 538
[1] | Additions to other real estate owned (“OREO”) may include transfers from loans, transfers from closed branches, and capitalized improvements to existing OREO properties.

X
- Definition Other real estate gross gains. + References No definition available. + Details
Name: | fusb_OtherRealEstateGrossGains
Namespace Prefix: | fusb_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Other real estate gross losses. + References No definition available. + Details
Name: | fusb_OtherRealEstateGrossLosses
Namespace Prefix: | fusb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Other real estate net income loss. + References No definition available. + Details
Name: | fusb_OtherRealEstateNetIncomeLoss
Namespace Prefix: | fusb_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The charge against earnings in the period to reduce the carrying amount of real property to fair value. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 230 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 28 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482740/230-10-45-28 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 360 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482099/360-10-50-2 + Details
Name: | us-gaap_ImpairmentOfRealEstate
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_OtherRealEstateAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The cash inflow associated with the sale of other real estate not otherwise defined in the taxonomy. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 12 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482740/230-10-45-12 + Details
Name: | us-gaap_ProceedsFromSaleOfOtherRealEstate
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Carrying amount as of the balance sheet date of land and buildings obtained through foreclosure proceedings or defeasance in full or partial satisfaction of a debt arrangement. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 310 -SubTopic 20 -Name Accounting Standards Codification -Section 40 -Paragraph 7 -Publisher FASB -URI https://asc.fasb.org/1943274/2147481628/310-20-40-7 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 310 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 3 -Publisher FASB -URI https://asc.fasb.org/1943274/2147481990/310-10-45-3 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 310 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 11 -Publisher FASB -URI https://asc.fasb.org/1943274/2147481962/310-10-50-11 + Details
Name: | us-gaap_RealEstateAcquiredThroughForeclosure
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Value transferred from mortgage loans to real estate owned (REO) in noncash transactions. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 4 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482913/230-10-50-4 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 3 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482913/230-10-50-3 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 5 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482913/230-10-50-5 + Details
Name: | us-gaap_TransferToOtherRealEstate
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration