Defined Benefit and Other Postretirement Benefits - Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 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
Interest cost	62	73
Expected return on plan assets	(24)	(26)
Recognized net loss due to lump sum settlements	0	25
Net periodic benefit cost	48	85
Supplemental Retirement Plan [Member]
Net periodic benefit cost [Abstract]
Service cost	11	17
Interest cost	477	520
Amortization of prior service cost	28	28
Recognized net actuarial loss	95	77
Net periodic benefit cost	$ 611	$ 642