Long-term Debt Other Long-term Debt (Details) - USD ($) $ in Thousands		6 Months Ended
		Jun. 30, 2023		Dec. 31, 2022		Nov. 06, 2020	Oct. 10, 2007	Aug. 10, 2007	Aug. 08, 2007	May 20, 2005	[4]	Sep. 04, 2003
Debt Instruments [Abstract]
Subordinated notes, net of unamortized debt issuance costs:	[1]	$ 93,796		$ 98,674
Trust preferred subordinated debentures	[2]	60,267		60,265
Total long-term debt		154,063		158,939
Southside Statutory Trust III, net of unamortized debt issuance costs
Debt Instruments [Abstract]
Trust preferred subordinated debentures		20,575	[2],[3]	20,573	[2],[3]							$ 20,619
Unamortized Debt Issuance Expense		44		46
Southside Statutory Trust IV
Debt Instruments [Abstract]
Trust preferred subordinated debentures		23,196	[2]	23,196	[2]				$ 23,196
Southside Statutory Trust V
Debt Instruments [Abstract]
Trust preferred subordinated debentures		12,887	[2]	12,887	[2]			$ 12,887
Magnolia Trust Company I
Debt Instruments [Abstract]
Trust preferred subordinated debentures		3,609	[2]	3,609	[2]		$ 3,600			$ 3,609
3.875% Subordinated Notes
Debt Instruments [Abstract]
Subordinated notes, net of unamortized debt issuance costs:	[1],[5]	93,796		98,674
Unamortized Debt Issuance Expense		$ 1,200		$ 1,300
Stated interest rate		3.875%				3.875%
Minimum
Debt Instruments [Abstract]
Subordinated notes, remaining maturity, greater than		1 year

[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 debt issuance costs reflected in the carrying amount of the Southside Statutory Trust III junior subordinated debentures totaled $44,000 at June 30, 2023 and $46,000 at December 31, 2022.

[4] 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

[5] The unamortized discount and debt issuance costs reflected in the carrying amount of the subordinated notes totaled approximately $1.2 million at June 30, 2023 and $1.3 million at December 31, 2022.