Defined Benefit and Other Postretirement Benefits - Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 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	$ 28	$ 63	$ 86	$ 189
Interest cost	48	43	144	129
Expected return on plan assets	(30)	(33)	(90)	(98)
Recognized net loss due to lump sum settlements	0	183	0	183
Recognized net actuarial loss	52	149	172	446
Net periodic benefit cost	98	405	312	849
Supplemental Retirement Plan [Member]
Net periodic benefit cost [Abstract]
Service cost	18	19	54	57
Interest cost	316	277	962	847
Amortization of prior service cost	28	28	83	84
Recognized net actuarial loss	243	295	742	896
Net periodic benefit cost	$ 605	$ 619	$ 1,841	$ 1,884