Defined Benefit and Other Postretirement Benefits - Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Trustmark Capital Accumulation Plan [Member] | Trustmark Corporation Pension Plan for Certain Employees of Acquired Financial Institutions [Member]
Net periodic benefit cost [Abstract]
Service cost	$ 9	$ 10
Interest cost	69	62
Expected return on plan assets	(32)	(24)
Recognized net (gain) loss due to lump sum settlements	(50)	0
Recognized net actuarial (gain) loss	(2)	0
Net periodic benefit cost	(6)	48
Supplemental Retirement Plan [Member]
Net periodic benefit cost [Abstract]
Service cost	4	11
Interest cost	495	477
Amortization of prior service cost	4	28
Recognized net actuarial (gain) loss	73	95
Net periodic benefit cost	$ 576	$ 611