Cash and Due from Banks (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010
Cash and Cash Equivalents [Abstract]
Average reserve balances with Federal Reserve Bank	$ 36.6	$ 31.8

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