Defined Benefit and Other Postretirement Benefits - Additional Information (Details) - USD ($)	3 Months Ended	12 Months Ended
Mar. 31, 2017	Dec. 31, 2017
Trustmark Capital Accumulation Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Years of service required to vest	3 years
Spin-Off 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

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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