Defined Benefit and Other Postretirement Benefits - Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Trustmark Capital Accumulation Plan [Member] | Trustmark Corporation Pension Plan for Certain Employees of Acquired Financial Institutions [Member]
Net periodic benefit cost [Abstract]
Service cost	$ 13	$ 29	$ 26	$ 58
Interest cost	73	48	146	96
Expected return on plan assets	(27)	(30)	(53)	(60)
Recognized net loss due to lump sum settlements	0	0	25	0
Recognized net actuarial loss	0	60	0	120
Net periodic benefit cost	59	107	144	214
Supplemental Retirement Plan [Member]
Net periodic benefit cost [Abstract]
Service cost	17	18	34	36
Interest cost	498	316	1,018	646
Amortization of prior service cost	27	27	55	55
Recognized net actuarial loss	69	244	146	499
Net periodic benefit cost	$ 611	$ 605	$ 1,253	$ 1,236