Cover Page - shares	9 Months Ended
	Sep. 30, 2023	Nov. 02, 2023
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2023
Document Transition Report	false
Entity File Number	000-06253
Entity Registrant Name	SIMMONS FIRST NATIONAL CORP
Entity Incorporation, State or Country Code	AR
Entity Tax Identification Number	71-0407808
Entity Address, Address Line One	501 Main Street
Entity Address, City or Town	Pine Bluff
Entity Address, State or Province	AR
Entity Address, Postal Zip Code	71601
City Area Code	870
Local Phone Number	541-1000
Title of 12(b) Security	Common stock, par value $0.01 per share
Trading Symbol	SFNC
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		125,168,597
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Central Index Key	0000090498
Current Fiscal Year End Date	--12-31