Defined Benefit and Other Postretirement Benefits - Additional Information (Details) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Recognized net loss due to defined benefit plan termination	$ 17,644,000		$ 17,644,000
Trustmark Capital Accumulation Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Years of service required to vest			3 years
Defined benefit plan, additional asset contributions on termination basis	17,600,000
Trustmark Capital Accumulation Plan [Member] | Scenario Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Trustmark's minimum required contribution to the Trustmark Corporation Pension Plan for Certain Employees of Acquired Financial Institutions					$ 0
Trustmark Capital Accumulation Plan [Member] | Trustmark Corporation Pension Plan for Certain Employees of Acquired Financial Institutions [Member]
Defined Benefit Plan Disclosure [Line Items]
Recognized net loss due to defined benefit plan termination	$ 17,644,000	$ 0	$ 17,644,000	$ 0