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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
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Business Acquisition [Line Items] |  |  |  |
Total Assets | $ 0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets | $ 1,845,543 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets | $ 234,960 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets |
Somerville Bank & Trust Company [Member] |  |  |  |
Business Acquisition [Line Items] |  |  |  |
Number of branches acquired | 5 trmk_ProposedBusinessAcquisitionNumberOfBranchesToBeAcquired / us-gaap_BusinessAcquisitionAxis = trmk_SomervilleBankTrustCompanyMember |  |  |
Total Assets | 219,600 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets / us-gaap_BusinessAcquisitionAxis = trmk_SomervilleBankTrustCompanyMember |  |  |
Oxford, Mississippi Branches [Member] |  |  |  |
Business Acquisition [Line Items] |  |  |  |
Number of branches acquired |  |  |  | 2 trmk_ProposedBusinessAcquisitionNumberOfBranchesToBeAcquired / us-gaap_BusinessAcquisitionAxis = trmk_OxfordMississippiBranchesMember
Deposits |  |  |  | $ 11,700 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesOther / us-gaap_BusinessAcquisitionAxis = trmk_OxfordMississippiBranchesMember

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- Definition The number of branches owned by the business to be acquired by the entity. + References No definition available. + Details
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- Definition Amount of assets acquired at the acquisition date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6910749&loc=d3e4845-128472 + Details
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- Definition Amount of other liabilities due within one year or within the normal operating cycle, if longer, assumed at the acquisition date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6910749&loc=d3e4845-128472 + Details
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- Details
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