Defined Benefit and Other Postretirement Benefits - Net Periodic Benefit Cost for Plan and Continuing plan (Details) - The Continuing 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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Net periodic benefit cost [Abstract]
Service cost	$ 53	$ 70	$ 106	$ 139
Interest cost	90	83	180	166
Expected return on plan assets	(50)	(57)	(101)	(114)
Recognized net loss due to lump sum settlements	63	40	94	80
Recognized net actuarial loss	93	143	186	285
Net periodic benefit cost	$ 249	$ 279	$ 465	$ 556