Defined Benefit and Other Postretirement Benefits - Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 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	$ 28	$ 39	$ 86
Interest cost	73	48	219	144
Expected return on plan assets	(27)	(30)	(80)	(90)
Recognized net loss due to lump sum settlements	0	0	25	0
Recognized net actuarial loss	0	52	0	172
Net periodic benefit cost	59	98	203	312
Supplemental Retirement Plan [Member]
Net periodic benefit cost [Abstract]
Service cost	17	18	51	54
Interest cost	497	316	1,515	962
Amortization of prior service cost	28	28	83	83
Recognized net actuarial loss	70	243	216	742
Net periodic benefit cost	$ 612	$ 605	$ 1,865	$ 1,841