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Business Combinations, BancTrust Financial Group (Details) (USD $) | 3 Months Ended | 12 Months Ended | 0 Months Ended | 3 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | --- | ---
Mar. 31, 2014 | Dec. 31, 2014 | Feb. 15, 2013 | Dec. 31, 2013 | Dec. 31, 2013 | Dec. 31, 2012
Business Acquisition [Line Items] |  |  |  |  |  |
Decrease in goodwill with a corresponding increase in deferred tax asset as measurement period adjustment | $ 7,400,000 us-gaap_GoodwillPeriodIncreaseDecrease |  |  |  |  |
Assets [Abstract] |  |  |  |  |  |
Total Assets |  | 0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets |  | 1,845,543,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets | 1,845,543,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets | 234,960,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets
Liabilities [Abstract] |  |  |  |  |  |
Total Liabilities |  | 0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities |  | 1,821,066,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities | 1,821,066,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities | 209,322,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities
Goodwill |  | 365,500,000 us-gaap_Goodwill |  | 372,851,000 us-gaap_Goodwill | 372,851,000 us-gaap_Goodwill | 291,104,000 us-gaap_Goodwill
Amortization period of acquired intangible asset |  | 20 years |  |  |  |
BancTrust Financial Group, Inc. [Member] |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |
Age of acquired entity |  |  | 26 years |  |  |
Preferred stock and warrants repurchased |  |  | 50,000,000 us-gaap_IssuanceOfStockAndWarrantsForServicesOrClaims / us-gaap_BusinessAcquisitionAxis = trmk_BanctrustFinancialGroupIncMember |  |  |
Issued value of preferred stock associated warrant under capital purchase program |  |  | 52,600,000 trmk_IssuedValueOfPreferredStockAssociatedWarrantUnderCapitalPurchaseProgram / us-gaap_BusinessAcquisitionAxis = trmk_BanctrustFinancialGroupIncMember |  |  |
Equity issued, per share of acquired company (in shares) |  |  | 0.125 trmk_ProposedBusinessAcquisitionEquityToBeIssuedPerShareOfAcquiredCompany / us-gaap_BusinessAcquisitionAxis = trmk_BanctrustFinancialGroupIncMember |  |  |
Decrease in acquired non covered loans as measurement period adjustment |  |  |  | 6,800,000 trmk_BusinessCombinationIncreaseDecreaseInAcquiredNonCoveredLoansAsMeasurementPeriodAdjustment / us-gaap_BusinessAcquisitionAxis = trmk_BanctrustFinancialGroupIncMember | 6,800,000 trmk_BusinessCombinationIncreaseDecreaseInAcquiredNonCoveredLoansAsMeasurementPeriodAdjustment / us-gaap_BusinessAcquisitionAxis = trmk_BanctrustFinancialGroupIncMember |
Decrease in Premises and equipment as measurement period adjustment |  |  |  |  | 627,000 trmk_BusinessCombinationIncreaseDecreaseInPremisesAndEquipmentAsMeasurementPeriodAdjustment / us-gaap_BusinessAcquisitionAxis = trmk_BanctrustFinancialGroupIncMember |
Decrease in other real estate as measurement period adjustment |  |  |  |  | 2,600,000 trmk_BusinessCombinationIncreaseDecreaseInOtherRealEstateAsMeasurementPeriodAdjustment / us-gaap_BusinessAcquisitionAxis = trmk_BanctrustFinancialGroupIncMember |
Increase in deferred tax asset as measurement period adjustment |  |  |  |  | 3,400,000 trmk_BusinessCombinationIncreaseDecreaseInDeferredTaxAssetAsMeasurementPeriodAdjustment / us-gaap_BusinessAcquisitionAxis = trmk_BanctrustFinancialGroupIncMember |
Increase in goodwill as measurement period adjustment |  |  |  |  | 6,300,000 us-gaap_GoodwillTranslationAndPurchaseAccountingAdjustments / us-gaap_BusinessAcquisitionAxis = trmk_BanctrustFinancialGroupIncMember |
Transfer to other real estate as measurement period adjustment |  |  |  |  | 1,600,000 us-gaap_TransferToOtherRealEstate / us-gaap_BusinessAcquisitionAxis = trmk_BanctrustFinancialGroupIncMember |
Assets [Abstract] |  |  |  |  |  |
Cash and due from banks |  |  | 141,616,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents / us-gaap_BusinessAcquisitionAxis = trmk_BanctrustFinancialGroupIncMember |  |  |
Securities available for sale |  |  | 528,016,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsMarketableSecurities / us-gaap_BusinessAcquisitionAxis = trmk_BanctrustFinancialGroupIncMember |  |  |
Loans held for sale |  |  | 1,050,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsOther / us-gaap_BusinessAcquisitionAxis = trmk_BanctrustFinancialGroupIncMember |  |  |
Acquired noncovered loans |  |  | 944,235,000 trmk_BusinessAcquisitionPurchasePriceAllocationLhfiLoansAndLeasesExcludingCoveredLoans / us-gaap_BusinessAcquisitionAxis = trmk_BanctrustFinancialGroupIncMember |  |  |
Premises and equipment, net |  |  | 54,952,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment / us-gaap_BusinessAcquisitionAxis = trmk_BanctrustFinancialGroupIncMember |  |  |
Identifiable intangible assets |  |  | 33,498,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill / us-gaap_BusinessAcquisitionAxis = trmk_BanctrustFinancialGroupIncMember |  |  |
Other real estate |  |  | 40,103,000 trmk_BusinessAcquisitionOtherRealEstateAcquired / us-gaap_BusinessAcquisitionAxis = trmk_BanctrustFinancialGroupIncMember |  |  |
Other assets |  |  | 109,423,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets / us-gaap_BusinessAcquisitionAxis = trmk_BanctrustFinancialGroupIncMember |  |  |
Total Assets |  |  | 1,852,893,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets / us-gaap_BusinessAcquisitionAxis = trmk_BanctrustFinancialGroupIncMember |  |  |
Liabilities [Abstract] |  |  |  |  |  |
Deposits |  |  | 1,740,254,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesOther / us-gaap_BusinessAcquisitionAxis = trmk_BanctrustFinancialGroupIncMember |  |  |
Other borrowings |  |  | 64,051,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedFinancialLiabilities / us-gaap_BusinessAcquisitionAxis = trmk_BanctrustFinancialGroupIncMember |  |  |
Other liabilities |  |  | 16,761,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther / us-gaap_BusinessAcquisitionAxis = trmk_BanctrustFinancialGroupIncMember |  |  |
Total Liabilities |  |  | 1,821,066,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities / us-gaap_BusinessAcquisitionAxis = trmk_BanctrustFinancialGroupIncMember |  |  |
Net identified assets acquired at fair value |  |  | 31,827,000 us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerSharePlannedSaleInvestmentsNotIdentifiedValue / us-gaap_BusinessAcquisitionAxis = trmk_BanctrustFinancialGroupIncMember |  |  |
Goodwill |  |  | 74,247,000 us-gaap_Goodwill / us-gaap_BusinessAcquisitionAxis = trmk_BanctrustFinancialGroupIncMember |  |  |
Equity issued (in shares) |  |  | 2,240,000 trmk_ProposedBusinessAcquisitionEquityToBeIssued / us-gaap_BusinessAcquisitionAxis = trmk_BanctrustFinancialGroupIncMember |  |  |
Business acquisition, equity issued, value assigned |  |  | 53,500,000 us-gaap_BusinessAcquisitionEquityInterestIssuedOrIssuableValueAssigned / us-gaap_BusinessAcquisitionAxis = trmk_BanctrustFinancialGroupIncMember |  |  |
Business acquisition, closing stock price (in dollars per share) |  |  | $ 23.83 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerShareWeightedAveragePriceOfSharesPurchased / us-gaap_BusinessAcquisitionAxis = trmk_BanctrustFinancialGroupIncMember |  |  |
Number of markets entered due to acquisition |  | 15 trmk_NumberOfMarketsEnteredDueToAcquisition / us-gaap_BusinessAcquisitionAxis = trmk_BanctrustFinancialGroupIncMember |  |  |  |
Amortization period of acquired intangible asset |  | 10 years |  |  |  |
Net assets acquired at fair value |  |  | 106,074,000 us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireeFairValue1 / us-gaap_BusinessAcquisitionAxis = trmk_BanctrustFinancialGroupIncMember |  |  |
Business acquisition, total transaction expenses |  |  |  |  | 9,400,000 trmk_BusinessAcquisitionTotalTransactionExpenses / us-gaap_BusinessAcquisitionAxis = trmk_BanctrustFinancialGroupIncMember |
Business acquisition, severance expense |  |  |  |  | 1,400,000 trmk_BusinessAcquisitionSeveranceExpense / us-gaap_BusinessAcquisitionAxis = trmk_BanctrustFinancialGroupIncMember |
Business acquisition, contract termination and other expenses |  |  |  |  | $ 7,900,000 trmk_BusinessAcquisitionContractTerminationAndOtherExpenses / us-gaap_BusinessAcquisitionAxis = trmk_BanctrustFinancialGroupIncMember |

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- Definition Amount of other liabilities due after one year or 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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