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Defined Benefit and Other Postretirement Benefits - Net Periodic Benefit Cost (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]      
Net periodic benefit cost [Abstract]      
Service cost $ 36 $ 40 $ 52
Interest cost 275 246 292
Expected return on plan assets (125) (96) (107)
Recognized net (gain) loss due to lump sum settlements (79) (13) 25
Recognized net actuarial loss (7) 0 0
Net periodic benefit cost 100 177 262
Other changes in plan assets and benefit obligation recognized in other comprehensive income (loss), before taxes:      
Total recognized in other comprehensive income (loss) 27 (339) 9
Total recognized in net periodic benefit cost and other comprehensive income (loss) $ 127 $ (162) $ 271
Weighted-average assumptions as of end of year [Abstract]      
Discount rate for benefit obligation 4.99% 5.30% 4.67%
Discount rate for net periodic benefit cost 5.30% 4.67% 4.88%
Expected long-term return on plan assets 5.00% 5.00% 5.00%
Supplemental Retirement Plan [Member]      
Net periodic benefit cost [Abstract]      
Service cost $ 15 $ 45 $ 69
Interest cost 1,921 1,851 2,013
Amortization of prior service cost 15 111 111
Recognized net actuarial loss 261 346 284
Net periodic benefit cost 2,212 2,353 2,477
Other changes in plan assets and benefit obligation recognized in other comprehensive income (loss), before taxes:      
Net (gain) loss 585 (1,355) 479
Amortization of prior service cost (15) (111) (111)
Total recognized in other comprehensive income (loss) 570 (1,466) 368
Total recognized in net periodic benefit cost and other comprehensive income (loss) $ 2,782 $ 887 $ 2,845
Weighted-average assumptions as of end of year [Abstract]      
Discount rate for benefit obligation 4.99% 5.30% 4.67%
Discount rate for net periodic benefit cost 5.30% 4.67% 4.88%