Defined Benefit and Other Postretirement Benefits - Net Periodic Benefit Cost for Plan and Continuing plan (Details) - Trustmark Capital Accumulation Plan [Member] - Trustmark Corporation Pension Plan for Certain Employees of Acquired Financial Institutions [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Net periodic benefit cost [Abstract]
Service cost	$ 63	$ 53	$ 127	$ 106
Interest cost	61	90	121	180
Expected return on plan assets	(39)	(50)	(77)	(101)
Recognized net loss due to lump sum settlements	40	63	40	94
Recognized net actuarial loss	82	93	163	186
Net periodic benefit cost	$ 207	$ 249	$ 374	$ 465