Loans And Leases - Schedule of Amortized Cost Basis of Collateral Dependent Loans (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2025	Dec. 31, 2024
Total loans individually evaluated	$ 3,097	$ 7,601
Real Estate [Member] \| Construction, Land Development and Other Land Loans [Member]
Total loans individually evaluated	2,304	2,489
Real Estate [Member] \| Secured by Real Estate 1-4 Family Residential Properties [Member]
Total loans individually evaluated	391	1,402
Real Estate [Member] \| Secured by Non-residential Commercial Real Estate [Member]
Total loans individually evaluated	363	383
Commercial And Industrial Loans [Member]
Total loans individually evaluated	39	3,327
Real Estate [Member]
Total loans individually evaluated	3,058	4,274
Real Estate [Member] \| Real Estate [Member] \| Construction, Land Development and Other Land Loans [Member]
Total loans individually evaluated	2,304	2,489
Real Estate [Member] \| Real Estate [Member] \| Secured by Real Estate 1-4 Family Residential Properties [Member]
Total loans individually evaluated	391	1,402
Real Estate [Member] \| Real Estate [Member] \| Secured by Non-residential Commercial Real Estate [Member]
Total loans individually evaluated	363	383
Other [Member]
Total loans individually evaluated	39	3,327
Other [Member] \| Commercial And Industrial Loans [Member]
Total loans individually evaluated	$ 39	$ 3,327

FIRST US BANCSHARES, INC. 10-Q