Document And Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Mar. 03, 2021	Jun. 30, 2020
Document And Entity Information
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Document Transition Report	false
Entity Registrant Name	FIRST BANCSHARES INC /MS/
Entity Central Index Key	0000947559
Trading Symbol	FBMS
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 File Number	333-94288
Entity Address, Address Line One	6480 U.S. Hwy. 98 West, Suite A
Entity Address, City or Town	Hattiesburg
Entity Address, Country	MS
Entity Address, Postal Zip Code	39402
Entity Incorporation, State or Country Code	MS
Entity Tax Identification Number	64-0862173
City Area Code	601
Local Phone Number	268-8998
Title of 12(b) Security	Common Stock
Security Exchange Name	NASDAQ
Entity Common Stock, Shares Outstanding		21,018,319
Entity Public Float			$ 458.3
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Entity Well-known Seasoned Issuer	No
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Voluntary Filers	No
ICFR Auditor Attestation Flag	true