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Defined Benefit and Other Postretirement Benefits - Plan Benefit Obligation, Plan Assets and Funded Status of the Plan (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Trustmark Capital Accumulation Plan [Member] | Trustmark Corporation Pension Plan for Certain Employees of Acquired Financial Institutions [Member]      
Change in benefit obligation [Roll Forward]      
Benefit obligation, beginning of year $ 5,531 $ 5,923  
Service cost 36 40 $ 52
Interest cost 275 246 292
Actuarial (gain) loss (23) (214)  
Benefits paid (1,500) (464)  
Benefit obligation, end of year 4,319 5,531 5,923
Change in plan assets [ Roll Forward]      
Fair value of plan assets, beginning of year 2,685 2,403  
Actual return on plan assets 161 233  
Employer contributions 299 513  
Benefit payments (1,500) (464)  
Fair value of plan assets, end of year 1,645 2,685 2,403
Funded status at end of year - net liability (2,674) (2,846)  
Amounts recognized in accumulated other comprehensive loss [Abstract]      
Net (gain) loss - amount recognized (574) (601)  
Actuarial (gain) loss included in benefit obligation:      
Change in discount rate 120 (344)  
Change in mortality table 0 0  
Other (143) 130  
Actuarial (gain) loss (23) (214)  
Supplemental Retirement Plan [Member]      
Change in benefit obligation [Roll Forward]      
Benefit obligation, beginning of year 38,162 41,619  
Service cost 15 45 69
Interest cost 1,921 1,851 2,013
Actuarial (gain) loss 845 (1,009)  
Benefits paid (3,868) (4,344)  
Benefit obligation, end of year 37,075 38,162 $ 41,619
Change in plan assets [ Roll Forward]      
Employer contributions 3,868 4,344  
Benefit payments (3,868) (4,344)  
Funded status at end of year - net liability (37,075) (38,162)  
Amounts recognized in accumulated other comprehensive loss [Abstract]      
Net (gain) loss - amount recognized 7,465 6,880  
Prior service cost 0 15  
Amounts recognized 7,465 6,895  
Actuarial (gain) loss included in benefit obligation:      
Change in discount rate 788 (1,794)  
Change in mortality table 0 0  
Other 57 785  
Actuarial (gain) loss $ 845 $ (1,009)