Defined Benefit and Other Postretirement Benefits - Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Trustmark Capital Accumulation Plan [Member] | Trustmark Corporation Pension Plan for Certain Employees of Acquired Financial Institutions [Member]
Net periodic benefit cost [Abstract]
Service cost	$ 29	$ 63	$ 58	$ 126
Interest cost	48	43	96	86
Expected return on plan assets	(30)	(32)	(60)	(65)
Recognized net actuarial loss	60	148	120	297
Net periodic benefit cost	107	222	214	444
Supplemental Retirement Plan [Member]
Net periodic benefit cost [Abstract]
Service cost	18	19	36	38
Interest cost	316	277	646	570
Amortization of prior service cost	27	28	55	56
Recognized net actuarial loss	244	295	499	601
Net periodic benefit cost	$ 605	$ 619	$ 1,236	$ 1,265