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Business Combinations (Details) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Jul. 26, 2013
Branch
Business Acquisition [Line Items]        
Total Assets $ 0us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets $ 1,845,543us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets $ 234,960us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets  
Somerville Bank & Trust Company [Member]        
Business Acquisition [Line Items]        
Number of branches acquired 5trmk_ProposedBusinessAcquisitionNumberOfBranchesToBeAcquired
/ us-gaap_BusinessAcquisitionAxis
= trmk_SomervilleBankTrustCompanyMember		      
Total Assets 219,600us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets
/ us-gaap_BusinessAcquisitionAxis
= trmk_SomervilleBankTrustCompanyMember		      
Oxford, Mississippi Branches [Member]        
Business Acquisition [Line Items]        
Number of branches acquired       2trmk_ProposedBusinessAcquisitionNumberOfBranchesToBeAcquired
/ us-gaap_BusinessAcquisitionAxis
= trmk_OxfordMississippiBranchesMember
Deposits       $ 11,700us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesOther
/ us-gaap_BusinessAcquisitionAxis
= trmk_OxfordMississippiBranchesMember