v3.26.1
Cover - USD ($)
 12 Months Ended
Dec. 31, 2025
Mar. 16, 2026
Jun. 30, 2025
Document Information [Line Items]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2025    
Current Fiscal Year End Date --12-31    
Document Transition Report false    
Entity File Number 001-37621    
Entity Registrant Name FIRST GUARANTY BANCSHARES, INC.    
Entity Incorporation, State or Country Code LA    
Entity Tax Identification Number 26-0513559    
Entity Address, Address Line One 400 East Thomas Street    
Entity Address, City or Town Hammond,    
Entity Address, State or Province LA    
Entity Address, Postal Zip Code 70401    
City Area Code (985)    
Local Phone Number 345-7685    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Non-accelerated Filer    
Entity Small Business true    
Entity Emerging Growth Company false    
ICFR Auditor Attestation Flag false    
Document Financial Statement Error Correction [Flag] false    
Entity Shell Company false    
Entity Public Float     $ 43,592,707
Shares Outstanding (in shares)   15,793,433  
Documents Incorporated by Reference
DOCUMENTS INCORPORATED BY REFERENCE:
 
(1)Proxy Statement for the 2026 Annual Meeting of Shareholders of the Registrant (Part III).
    
Entity Central Index Key 0001408534    
Document Fiscal Year Focus 2025    
Document Fiscal Period Focus FY    
Amendment Flag false    
Common Stock $1 Par      
Document Information [Line Items]      
Title of 12(b) Security Common Stock, $1 par value    
Trading Symbol FGBI    
Security Exchange Name NASDAQ    
Depositary Shares (each representing a 1/40th interest in a share of 6.75% Series A Fixed-Rate Non-Cumulative perpetual preferred stock)      
Document Information [Line Items]      
Title of 12(b) Security Depositary Shares (each representing a 1/40th interest in a share of 6.75% Series A Fixed-Rate Non-Cumulative perpetual preferred stock)    
Trading Symbol FGBIP    
Security Exchange Name NASDAQ