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
	Mar. 31, 2019	Mar. 31, 2018
Net periodic benefit cost [Abstract]
Service cost	$ 53	$ 69
Interest cost	90	83
Expected return on plan assets	(51)	(57)
Recognized net loss due to lump sum settlements	31	40
Recognized net actuarial loss	93	142
Net periodic benefit cost	$ 216	$ 277