v3.26.1
Long-term Debt LT Debt Interest Rates (Details) - USD ($)
$ in Thousands
 6 Months Ended
Aug. 10, 2007
Aug. 08, 2007
May 20, 2005
Sep. 04, 2003
Jun. 30, 2026
Dec. 31, 2025
Aug. 14, 2025
Oct. 10, 2007
Debt Instrument [Line Items]                
Other long-term debt [1]         $ 60,282 $ 60,279    
7.0% Subordinated Notes Due 2035                
Debt Instrument [Line Items]                
Stated interest rate             7.00%  
Debt face amount             $ 150,000  
Southside Statutory Trust III                
Debt Instrument [Line Items]                
Debt Instrument, Variable Interest Rate, Type [Extensible Enumeration]         Secured Overnight Financing Rate (SOFR) [Member]      
Other long-term debt       $ 20,619 $ 20,590 [1],[2] 20,587 [1],[2]    
Basis on variable rate       3.20%        
Southside Statutory Trust IV                
Debt Instrument [Line Items]                
Debt Instrument, Variable Interest Rate, Type [Extensible Enumeration]         Secured Overnight Financing Rate (SOFR) [Member]      
Other long-term debt   $ 23,196     $ 23,196 [1] 23,196 [1]    
Basis on variable rate   1.56%            
Southside Statutory Trust V                
Debt Instrument [Line Items]                
Debt Instrument, Variable Interest Rate, Type [Extensible Enumeration]         Secured Overnight Financing Rate (SOFR) [Member]      
Other long-term debt $ 12,887       $ 12,887 [1] 12,887 [1]    
Basis on variable rate 2.51%              
Magnolia Trust Company I                
Debt Instrument [Line Items]                
Debt Instrument, Variable Interest Rate, Type [Extensible Enumeration]         Secured Overnight Financing Rate (SOFR) [Member]      
Other long-term debt     $ 3,609 [3]   $ 3,609 [1] $ 3,609 [1]   $ 3,600
Basis on variable rate [3]     2.06%          
[1] This debt consists of trust preferred securities that qualify under the risk-based capital guidelines as Tier 1 capital, subject to certain limitations.
[2] The unamortized debt issuance costs reflected in the carrying amount of the Southside Statutory Trust III junior subordinated debentures totaled $29,000 at June 30, 2026 and $32,000 at December 31, 2025.
[3] On October 10, 2007, as part of an acquisition we assumed $3.6 million of floating rate junior subordinated debentures issued in 2005 to Magnolia Trust Company I