Note 26 - Financial Statements - Parent Company Only - Balance Sheets for Business First Bancshares, Inc. (Parent Company) (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	May 01, 2020	Dec. 31, 2019
Assets:
Goodwill	$ 88,543	$ 59,894
Other Assets	9,642	11,105
Total Assets	5,990,460	4,726,378
Liabilities:
Accrued Interest Payable	2,092	1,354
Subordinated Debt	110,749	81,427
Subordinated Debt - Trust Preferred Securities	5,000	5,000		$ 5,000
Other Liabilities	27,419	26,783
Total Liabilities	5,409,979	4,293,010
Shareholders' Equity:
Preferred Stock	71,930	0
Common Stock	25,110	20,400
Additional Paid-in Capital	393,690	292,271
Retained Earnings	163,955	121,874
Accumulated Other Comprehensive Income (Loss)	(74,204)	(1,177)
Total Shareholders' Equity	580,481	433,368	$ 409,963		$ 285,097
Total Liabilities and Shareholders' Equity	5,990,460	4,726,378
Parent Company [Member]
Assets:
Cash	35,684	1,322
Investment in Subsidiaries	641,491	509,835
Fintech Funds	3,080	1,364
Goodwill	5,704	0
Income Taxes Receivable	8,739	6,464
Other Assets	1,794	1,003
Total Assets	696,492	519,988
Liabilities:
Accrued Interest Payable	80	0
Short Term Borrowings	9	20
Subordinated Debt	110,749	81,427
Subordinated Debt - Trust Preferred Securities	5,155	5,155
Other Liabilities	18	18
Total Liabilities	116,011	86,620
Shareholders' Equity:
Preferred Stock	71,930	0
Common Stock	25,110	20,400
Additional Paid-in Capital	393,690	292,271
Retained Earnings	163,955	121,874
Accumulated Other Comprehensive Income (Loss)	(74,204)	(1,177)
Total Shareholders' Equity	580,481	433,368
Total Liabilities and Shareholders' Equity	$ 696,492	$ 519,988