Cover Page - shares	9 Months Ended
	Sep. 30, 2024	Oct. 24, 2024
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2024
Document Transition Report	false
Entity File Number	001-38447
Entity Registrant Name	BUSINESS FIRST BANCSHARES, INC.
Entity Incorporation, State or Country Code	LA
Entity Tax Identification Number	20-5340628
Entity Address, Address Line One	500 Laurel Street, Suite 101
Entity Address, City or Town	Baton Rouge
Entity Address, State or Province	LA
Entity Address, Postal Zip Code	70801
City Area Code	225
Local Phone Number	248-7600
Title of 12(b) Security	Common Stock, par value $1.00 per share
Trading Symbol	BFST
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		29,541,455
Entity Central Index Key	0001624322
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q3
Amendment Flag	false
Current Fiscal Year End Date	--12-31