Defined Benefit and Other Postretirement Benefits - Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 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	$ 20	$ 26
Interest cost	61	73	123	146
Expected return on plan assets	(24)	(27)	(48)	(53)
Recognized net (gain) loss due to lump sum settlements	(13)	0	(13)	25
Net periodic benefit cost	34	59	82	144
Supplemental Retirement Plan [Member]
Net periodic benefit cost [Abstract]
Service cost	11	17	22	34
Interest cost	459	498	936	1,018
Amortization of prior service cost	27	27	55	55
Recognized net actuarial loss	84	69	179	146
Net periodic benefit cost	$ 581	$ 611	$ 1,192	$ 1,253