Note 24 - First US Bancshares, Inc. (Parent Company Only) Financial Information - Statements of Statements of Operations (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Income:
Expense									$ 5,965	$ 5,714
Net income (loss)	$ 1,477	$ 240	$ 359	$ 414	$ (1,866)	$ 635	$ 416	$ 404	2,490	(411)
FUSB [Member]
Income:
Dividend income, First US Bank									976	1,206
Total income									976	1,206
Expense									831	751
Gain before equity in undistributed income of subsidiaries									145	455
Equity in undistributed income of subsidiaries									2,345	(866)
Net income (loss)									$ 2,490	$ (411)