Defined Benefit and Other Postretirement Benefits - Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 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	$ 10	$ 13	$ 30	$ 39
Interest cost	62	73	185	219
Expected return on plan assets	(24)	(27)	(72)	(80)
Recognized net (gain) loss due to lump sum settlements	0	0	(13)	25
Net periodic benefit cost	48	59	130	203
Supplemental Retirement Plan [Member]
Net periodic benefit cost [Abstract]
Service cost	11	17	33	51
Interest cost	457	497	1,393	1,515
Amortization of prior service cost	28	28	83	83
Recognized net actuarial loss	84	70	263	216
Net periodic benefit cost	$ 580	$ 612	$ 1,772	$ 1,865