Defined Benefit and Other Postretirement Benefits - Net Periodic Benefit Cost for Plan and Continuing plan (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Net periodic benefit cost [Abstract]
Recognized net loss due to defined benefit plan termination	$ 17,644		$ 17,644
Trustmark Capital Accumulation Plan [Member] | Trustmark Corporation Pension Plan for Certain Employees of Acquired Financial Institutions [Member]
Net periodic benefit cost [Abstract]
Service cost	63	$ 108	126	$ 216
Interest cost	627	830	1,292	1,660
Expected return on plan assets	(108)	(1,022)	(216)	(2,044)
Recognized net loss due to lump sum settlements	0	2,248	0	2,671
Recognized net loss due to defined benefit plan termination	17,644	0	17,644	0
Recognized net actuarial loss	565	660	1,130	1,321
Net periodic benefit cost	$ 18,791	$ 2,824	$ 19,976	$ 3,824