Defined Benefit and Other Postretirement Benefits - Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Trustmark Capital Accumulation Plan [Member] | Trustmark Corporation Pension Plan for Certain Employees of Acquired Financial Institutions [Member]
Net periodic benefit cost [Abstract]
Service cost	$ 13	$ 29
Interest cost	73	48
Expected return on plan assets	(26)	(30)
Recognized net loss due to lump sum settlements	(25)	0
Recognized net actuarial loss	0	60
Net periodic benefit cost	85	107
Supplemental Retirement Plan [Member]
Net periodic benefit cost [Abstract]
Service cost	17	18
Interest cost	520	330
Amortization of prior service cost	28	28
Recognized net actuarial loss	77	255
Net periodic benefit cost	$ 642	$ 631