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Cash and Due from Banks (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013
Cash and Due from Banks [Abstract] |  |
Average reserve balances with Federal Reserve Bank | $ 75.6 trmk_AverageReserveBalancesWithFederalReserveBank | $ 57.6 trmk_AverageReserveBalancesWithFederalReserveBank

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- Definition 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. + References No definition available. + Details
Name: | trmk_AverageReserveBalancesWithFederalReserveBank
Namespace Prefix: | trmk_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Details
Name: | us-gaap_CashAndCashEquivalentsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration