v3.26.1
Long-term Debt Other Long-term Debt (Details) - USD ($)
$ in Thousands
 6 Months Ended
Jun. 30, 2026
Dec. 31, 2025
Aug. 14, 2025
Nov. 06, 2020
Oct. 10, 2007
Aug. 10, 2007
Aug. 08, 2007
May 20, 2005
 [6]
Sep. 04, 2003
Debt Instruments [Abstract]                  
Subordinated notes, net of unamortized debt issuance costs [1] $ 147,587 $ 239,678              
Other long-term debt [2] 60,282 60,279              
Total long-term debt $ 207,869 299,957              
Minimum                  
Debt Instruments [Abstract]                  
Subordinated notes, remaining maturity, greater than 1 year                
3.875% Subordinated Notes                  
Debt Instruments [Abstract]                  
Stated interest rate       3.875%          
Subordinated notes, net of unamortized debt issuance costs [1],[3] $ 0 92,190              
Unamortized Debt Issuance Expense   810              
7.0% Subordinated Notes Due 2035                  
Debt Instruments [Abstract]                  
Stated interest rate     7.00%            
Subordinated notes, net of unamortized debt issuance costs [1],[4] 147,587 147,488              
Unamortized Debt Issuance Expense 2,400 2,500              
Southside Statutory Trust III                  
Debt Instruments [Abstract]                  
Other long-term debt 20,590 [2],[5] 20,587 [2],[5]             $ 20,619
Unamortized Debt Issuance Expense 29 32              
Southside Statutory Trust IV                  
Debt Instruments [Abstract]                  
Other long-term debt 23,196 [2] 23,196 [2]         $ 23,196    
Southside Statutory Trust V                  
Debt Instruments [Abstract]                  
Other long-term debt 12,887 [2] 12,887 [2]       $ 12,887      
Magnolia Trust Company I                  
Debt Instruments [Abstract]                  
Other long-term debt $ 3,609 [2] $ 3,609 [2]     $ 3,600     $ 3,609  
[1] This debt consists of subordinated notes with a remaining maturity greater than one year that qualify under the risk-based capital guidelines as Tier 2 capital, subject to certain limitations.
[2] This debt consists of trust preferred securities that qualify under the risk-based capital guidelines as Tier 1 capital, subject to certain limitations.
[3] The unamortized discount and debt issuance costs reflected in the carrying amount of the subordinated notes totaled approximately $810,000 at December 31, 2025.
[4] The unamortized discount and debt issuance costs reflected in the carrying amount of the subordinated notes totaled approximately $2.4 million at June 30, 2026 and $2.5 million at December 31, 2025
[5] 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.
[6] 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