Business, Basis of Financial Statement Presentation and Principles of Consolidation (Details) $ in Millions	Oct. 10, 2018 USD ($) Loan County	Sep. 30, 2018 Office
Loans And Leases Receivable Disclosure [Line Items]
Number of offices | Office		198
Subsequent Events [Member]
Loans And Leases Receivable Disclosure [Line Items]
Number of loans held by Trustmark | Loan	1,787
Balance of outstanding loans | $	$ 239.7
Credit exposure of loans in FEMA designated disaster areas | $	$ 282.1
Florida [Member] | Subsequent Events [Member]
Loans And Leases Receivable Disclosure [Line Items]
Number of designated disaster area | County	12
Georgia [Member] | Subsequent Events [Member]
Loans And Leases Receivable Disclosure [Line Items]
Number of designated disaster area | County	20