Defined Benefit and Other Postretirement Benefits - Plan Benefit Obligation, Plan Assets and Funded Status of the Plan (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Trustmark Capital Accumulation Plan [Member] | Trustmark Corporation Pension Plan for Certain Employees of Acquired Financial Institutions [Member]
Change in benefit obligation [Roll Forward]
Benefit obligation, beginning of year	$ 6,907	$ 8,647
Service cost	52	115	$ 252
Interest cost	292	192	173
Actuarial (gain) loss	164	(1,882)
Benefits paid	(1,492)	(165)
Benefit obligation, end of year	5,923	6,907	8,647
Change in plan assets [ Roll Forward]
Fair value of plan assets, beginning of year	2,907	2,900
Actual return on plan assets	237	(285)
Employer contributions	751	457
Benefit payments	(1,492)	(165)
Fair value of plan assets, end of year	2,403	2,907	2,900
Funded status at end of year - net liability	(3,520)	(4,000)
Amounts recognized in accumulated other comprehensive income (loss) [Abstract]
Net (gain) loss - amount recognized	(262)	(271)
Actuarial (gain) loss included in benefit obligation:
Change in discount rate	124	(2,174)
Change in mortality table	(38)	0
Other	78	292
Actuarial (gain) loss	164	(1,882)
Supplemental Retirement Plan [Member]
Change in benefit obligation [Roll Forward]
Benefit obligation, beginning of year	43,201	55,035
Service cost	69	71	75
Interest cost	2,013	1,278	1,125
Actuarial (gain) loss	763	(9,195)
Benefits paid	(4,427)	(3,988)
Benefit obligation, end of year	41,619	43,201	$ 55,035
Change in plan assets [ Roll Forward]
Employer contributions	4,427	3,988
Benefit payments	(4,427)	(3,988)
Funded status at end of year - net liability	(41,619)	(43,201)
Amounts recognized in accumulated other comprehensive income (loss) [Abstract]
Net (gain) loss - amount recognized	8,235	7,756
Prior service cost	126	237
Amounts recognized	8,361	7,993
Actuarial (gain) loss included in benefit obligation:
Change in discount rate	649	(9,803)
Change in mortality table	(308)	0
Other	422	608
Actuarial (gain) loss	$ 763	$ (9,195)