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Cover Page - USD ($)
 12 Months Ended
Dec. 31, 2023
Feb. 23, 2024
Jun. 30, 2023
Cover [Abstract]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2023    
Current Fiscal Year End Date --12-31    
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 Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
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    
ICFR Auditor Attestation Flag true    
Document Financial Statement Error Correction false    
Entity Shell Company false    
Entity Public Float     $ 2,125,228,007
Entity Common Stock, Shares Outstanding   125,327,684  
Documents Incorporated by Reference
Portions of the Proxy Statement for the 2024 Annual Meeting of Shareholders of the Registrant to be held on April 23, 2024, are incorporated by reference into Part III of this Form 10-K.
    
Entity Central Index Key 0000090498    
Document Fiscal Year Focus 2023    
Document Fiscal Period Focus FY    
Amendment Flag false