Defined Benefit and Other Postretirement Benefits - Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Trustmark Capital Accumulation Plan [Member] | Trustmark Corporation Pension Plan for Certain Employees of Acquired Financial Institutions [Member]
Net periodic benefit cost [Abstract]
Service cost	$ 29	$ 63
Interest cost	48	43
Expected return on plan assets	(30)	(33)
Recognized net actuarial loss	60	149
Net periodic benefit cost	107	222
Supplemental Retirement Plan [Member]
Net periodic benefit cost [Abstract]
Service cost	18	19
Interest cost	330	293
Amortization of prior service cost	28	28
Recognized net actuarial loss	255	306
Net periodic benefit cost	$ 631	$ 646