Cash and Due from Banks - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Cash And Cash Equivalents [Abstract]
Average reserve balances with Federal Reserve Bank	$ 100.8	$ 94.7

For banks and other depository institutions, the calculated average reserve balance outstanding for the year as of the Balance Sheet date. Includes noninterest bearing balances with the Federal Reserve Banks.

No definition available.

Name:	trmk_AverageReserveBalancesWithFederalReserveBank
Namespace Prefix:	trmk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration