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
	Mar. 31, 2018	Mar. 31, 2017
Net periodic benefit cost [Abstract]
Service cost	$ 69	$ 63
Interest cost	83	665
Expected return on plan assets	(57)	(108)
Recognized net loss due to lump sum settlements	40	0
Recognized net actuarial loss	142	565
Net periodic benefit cost	$ 277	$ 1,185