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Securities Available for Sale and Held to Maturity (1) (Details) (USD $) | 3 Months Ended | 12 Months Ended | 3 Months Ended
--- | --- | --- | ---
Dec. 31, 2013 | Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Mar. 31, 2014
Estimated fair value [Abstract] |  |  |  |  |
Estimated fair value, less than 12 months | $ 2,108,340,000 trmk_EstimatedFairValueLessThan12Months | $ 590,965,000 trmk_EstimatedFairValueLessThan12Months | $ 2,108,340,000 trmk_EstimatedFairValueLessThan12Months |  |
Estimated fair value, 12 months or more | 24,415,000 trmk_EstimatedFairValue12MonthsOrMore | 522,230,000 trmk_EstimatedFairValue12MonthsOrMore | 24,415,000 trmk_EstimatedFairValue12MonthsOrMore |  |
Total estimated fair value | 2,132,755,000 trmk_TotalEstimatedFairValue | 1,113,195,000 trmk_TotalEstimatedFairValue | 2,132,755,000 trmk_TotalEstimatedFairValue |  |
Gross unrealized losses [Abstract] |  |  |  |  |
Gross unrealized (losses), less than 12 months | (47,362,000)trmk_GrossUnrealizedLossesLessThan12Months | (2,663,000)trmk_GrossUnrealizedLossesLessThan12Months | (47,362,000)trmk_GrossUnrealizedLossesLessThan12Months |  |
Gross unrealized (losses), 12 months or more | (426,000)trmk_GrossUnrealizedLosses12MonthsOrMore | (11,909,000)trmk_GrossUnrealizedLosses12MonthsOrMore | (426,000)trmk_GrossUnrealizedLosses12MonthsOrMore |  |
Total gross unrealized (losses) | (47,788,000)trmk_TotalGrossUnrealizedLosses | (14,572,000)trmk_TotalGrossUnrealizedLosses | (47,788,000)trmk_TotalGrossUnrealizedLosses |  |
Gains (losses) on investments [Abstract] |  |  |  |  |
Gross realized (losses) |  | 300,000 us-gaap_GainLossOnSaleOfSecuritiesNet | 485,000 us-gaap_GainLossOnSaleOfSecuritiesNet | 1,059,000 us-gaap_GainLossOnSaleOfSecuritiesNet |
Pledged to collateralize public deposits and securities sold under repurchase agreements and for other purposes as permitted by law | 2,475,000,000 trmk_PledgedCollateralizeDepositsAndSecuritiesSoldUnderRepurchaseAgreements | 2,457,000,000 trmk_PledgedCollateralizeDepositsAndSecuritiesSoldUnderRepurchaseAgreements | 2,475,000,000 trmk_PledgedCollateralizeDepositsAndSecuritiesSoldUnderRepurchaseAgreements |  |
Pledged securities providing additional contingency funding |  | 6,000,000 trmk_PledgedSecuritiesProvidingAdditionalContingencyFunding |  |  |
Available for Sale, amortized cost [Abstract] |  |  |  |  |
Due in one year or less |  | 18,088,000 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost |  |  |
Due after one year through five years |  | 137,976,000 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost |  |  |
Due after five years through ten years |  | 61,738,000 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost |  |  |
Due after ten years |  | 82,588,000 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost |  |  |
Total amortized cost, before mortgage-backed-securities |  | 300,390,000 trmk_TotalAmortizedCostBeforeMortgageBackedSecurities |  |  |
Mortgage-backed securities |  | 2,051,623,000 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateAmortizedCost |  |  |
Securities available for sale (at amortized cost) |  | 2,352,013,000 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCost |  |  |
Available for Sale, estimated fair value [Abstract] |  |  |  |  |
Due in one year or less |  | 18,236,000 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue |  |  |
Due after one year through five years |  | 142,016,000 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue |  |  |
Due after five years through ten years |  | 63,811,000 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue |  |  |
Due after ten years |  | 82,469,000 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue |  |  |
Total fair value, before mortgage-backed-securities |  | 306,532,000 trmk_TotalFairValueOfAvailableForSaleSecuritiesBeforeMortgageBackSecurities |  |  |
Mortgage-backed securities |  | 2,068,035,000 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue |  |  |
Securities available for sale (at fair value) | 2,194,154,000 us-gaap_AvailableForSaleSecurities | 2,374,567,000 us-gaap_AvailableForSaleSecurities | 2,194,154,000 us-gaap_AvailableForSaleSecurities |  |
Held to maturity, amortized cost [Abstract] |  |  |  |  |
Due in one year or less |  | 2,496,000 us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearNetCarryingAmount |  |  |
Due after one year through five years |  | 11,693,000 us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterOneThroughFiveYearsNetCarryingAmount |  |  |
Due after five years through ten years |  | 137,991,000 us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterFiveThroughTenYearsNetCarryingAmount |  |  |
Due after ten years |  | 12,296,000 us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterTenYearsNetCarryingAmount |  |  |
Total amortized cost, before mortgage-backed-securities |  | 164,476,000 trmk_TotalAmortizedCostHeldToMaturityBeforeMortgageBackedSecurities |  |  |
Mortgage-backed securities |  | 1,006,209,000 us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithoutSingleMaturityDateNetCarryingAmount |  |  |
Securities held to maturity (at amortized cost) | 1,168,728,000 us-gaap_HeldToMaturitySecurities | 1,170,685,000 us-gaap_HeldToMaturitySecurities | 1,168,728,000 us-gaap_HeldToMaturitySecurities |  |
Held to maturity, estimated fair value [Abstract] |  |  |  |  |
Due in one year or less |  | 2,513,000 us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearFairValue |  |  |
Due after one year through five years |  | 12,298,000 us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue |  |  |
Due after five years through ten years |  | 142,604,000 us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue |  |  |
Due after ten years |  | 13,090,000 us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterTenYearsFairValue |  |  |
Total fair value, before mortgage-backed-securities |  | 170,505,000 trmk_TotalFairValueOfHeldToMaturitySecuritiesBeforeMortgageBackSecurities |  |  |
Mortgage-backed securities |  | 1,012,341,000 us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue |  |  |
Securities held to maturity (at fair value) | 1,150,833,000 us-gaap_HeldToMaturitySecuritiesFairValue | 1,182,846,000 us-gaap_HeldToMaturitySecuritiesFairValue | 1,150,833,000 us-gaap_HeldToMaturitySecuritiesFairValue |  |
Reclassification of Securities available for sale to securities held to maturity | 1,099,000,000 trmk_ReclassificationOfAvailableForSaleToHeldToMaturitySecurities |  |  |  |
Net unrealized holding loss on AFS Securities at date of transfer | 46,600,000 trmk_OtherComprehensiveIncomeLossUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTaxAtDateOfTransfer |  |  |  |
Net unrealized holding loss on AFS Securities, net of tax at date of transfer | 28,800,000 trmk_OtherComprehensiveIncomeLossUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTaxAtDateOfTransfer |  |  |  |
Net unamortized, unrealized loss on transfer of securities |  | 40,400,000 trmk_AccumulatedOtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustment |  |  |
Net unamortized, unrealized loss on transfer of securities, net of tax |  | 24,900,000 us-gaap_AccumulatedOtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax |  |  |
Other-than-temporary impairments |  | 0 us-gaap_ImpairmentOfInvestments | 0 us-gaap_ImpairmentOfInvestments | 0 us-gaap_ImpairmentOfInvestments |
Available-for-sale Securities [Member] |  |  |  |  |
Gains (losses) on investments [Abstract] |  |  |  |  |
Proceeds from calls and sales of securities |  | 56,815,000 trmk_ProceedsFromCallsAndSalesOfSecurities / us-gaap_GainLossOnInvestmentsByCategoryAxis = us-gaap_AvailableforsaleSecuritiesMember | 224,853,000 trmk_ProceedsFromCallsAndSalesOfSecurities / us-gaap_GainLossOnInvestmentsByCategoryAxis = us-gaap_AvailableforsaleSecuritiesMember | 38,364,000 trmk_ProceedsFromCallsAndSalesOfSecurities / us-gaap_GainLossOnInvestmentsByCategoryAxis = us-gaap_AvailableforsaleSecuritiesMember |
Gross realized gains |  | 456,000 trmk_ProceedsFromMaturitiesCallsOfHeldToMaturitySecurities / us-gaap_GainLossOnInvestmentsByCategoryAxis = us-gaap_AvailableforsaleSecuritiesMember | 1,680,000 trmk_ProceedsFromMaturitiesCallsOfHeldToMaturitySecurities / us-gaap_GainLossOnInvestmentsByCategoryAxis = us-gaap_AvailableforsaleSecuritiesMember | 1,052,000 trmk_ProceedsFromMaturitiesCallsOfHeldToMaturitySecurities / us-gaap_GainLossOnInvestmentsByCategoryAxis = us-gaap_AvailableforsaleSecuritiesMember |
Gross realized (losses) |  | (156,000)us-gaap_GainLossOnSaleOfSecuritiesNet / us-gaap_GainLossOnInvestmentsByCategoryAxis = us-gaap_AvailableforsaleSecuritiesMember | (1,195,000)us-gaap_GainLossOnSaleOfSecuritiesNet / us-gaap_GainLossOnInvestmentsByCategoryAxis = us-gaap_AvailableforsaleSecuritiesMember | (2,000)us-gaap_GainLossOnSaleOfSecuritiesNet / us-gaap_GainLossOnInvestmentsByCategoryAxis = us-gaap_AvailableforsaleSecuritiesMember |
Held-to-maturity Securities [Member] |  |  |  |  |
Gains (losses) on investments [Abstract] |  |  |  |  |
Proceeds from calls and sales of securities |  | 0 trmk_ProceedsFromCallsAndSalesOfSecurities / us-gaap_GainLossOnInvestmentsByCategoryAxis = us-gaap_HeldtomaturitySecuritiesMember | 0 trmk_ProceedsFromCallsAndSalesOfSecurities / us-gaap_GainLossOnInvestmentsByCategoryAxis = us-gaap_HeldtomaturitySecuritiesMember | 335,000 trmk_ProceedsFromCallsAndSalesOfSecurities / us-gaap_GainLossOnInvestmentsByCategoryAxis = us-gaap_HeldtomaturitySecuritiesMember |
Gross realized gains |  | 0 trmk_ProceedsFromMaturitiesCallsOfHeldToMaturitySecurities / us-gaap_GainLossOnInvestmentsByCategoryAxis = us-gaap_HeldtomaturitySecuritiesMember | 0 trmk_ProceedsFromMaturitiesCallsOfHeldToMaturitySecurities / us-gaap_GainLossOnInvestmentsByCategoryAxis = us-gaap_HeldtomaturitySecuritiesMember | 9,000 trmk_ProceedsFromMaturitiesCallsOfHeldToMaturitySecurities / us-gaap_GainLossOnInvestmentsByCategoryAxis = us-gaap_HeldtomaturitySecuritiesMember |
U.S. Government Agency Obligations Issued by U.S. Government Agencies [Member] |  |  |  |  |
Estimated fair value [Abstract] |  |  |  |  |
Estimated fair value, less than 12 months | 68,908,000 trmk_EstimatedFairValueLessThan12Months / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember | 19,220,000 trmk_EstimatedFairValueLessThan12Months / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember | 68,908,000 trmk_EstimatedFairValueLessThan12Months / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember |  |
Estimated fair value, 12 months or more | 0 trmk_EstimatedFairValue12MonthsOrMore / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember | 32,656,000 trmk_EstimatedFairValue12MonthsOrMore / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember | 0 trmk_EstimatedFairValue12MonthsOrMore / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember |  |
Total estimated fair value | 68,908,000 trmk_TotalEstimatedFairValue / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember | 51,876,000 trmk_TotalEstimatedFairValue / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember | 68,908,000 trmk_TotalEstimatedFairValue / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember |  |
Gross unrealized losses [Abstract] |  |  |  |  |
Gross unrealized (losses), less than 12 months | (1,485,000)trmk_GrossUnrealizedLossesLessThan12Months / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember | (115,000)trmk_GrossUnrealizedLossesLessThan12Months / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember | (1,485,000)trmk_GrossUnrealizedLossesLessThan12Months / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember |  |
Gross unrealized (losses), 12 months or more | 0 trmk_GrossUnrealizedLosses12MonthsOrMore / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember | (711,000)trmk_GrossUnrealizedLosses12MonthsOrMore / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember | 0 trmk_GrossUnrealizedLosses12MonthsOrMore / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember |  |
Total gross unrealized (losses) | (1,485,000)trmk_TotalGrossUnrealizedLosses / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember | (826,000)trmk_TotalGrossUnrealizedLosses / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember | (1,485,000)trmk_TotalGrossUnrealizedLosses / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember |  |
Held to maturity, amortized cost [Abstract] |  |  |  |  |
Securities held to maturity (at amortized cost) | 0 us-gaap_HeldToMaturitySecurities / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember | 0 us-gaap_HeldToMaturitySecurities / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember | 0 us-gaap_HeldToMaturitySecurities / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember |  |
Held to maturity, estimated fair value [Abstract] |  |  |  |  |
Securities held to maturity (at fair value) | 0 us-gaap_HeldToMaturitySecuritiesFairValue / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember | 0 us-gaap_HeldToMaturitySecuritiesFairValue / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember | 0 us-gaap_HeldToMaturitySecuritiesFairValue / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember |  |
U.S. Government Agency Obligations Issued by U.S. Government Sponsored Agencies [Member] |  |  |  |  |
Estimated fair value [Abstract] |  |  |  |  |
Estimated fair value, less than 12 months | 138,478,000 trmk_EstimatedFairValueLessThan12Months / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | 9,948,000 trmk_EstimatedFairValueLessThan12Months / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | 138,478,000 trmk_EstimatedFairValueLessThan12Months / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember |  |
Estimated fair value, 12 months or more | 0 trmk_EstimatedFairValue12MonthsOrMore / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | 9,956,000 trmk_EstimatedFairValue12MonthsOrMore / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | 0 trmk_EstimatedFairValue12MonthsOrMore / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember |  |
Total estimated fair value | 138,478,000 trmk_TotalEstimatedFairValue / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | 19,904,000 trmk_TotalEstimatedFairValue / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | 138,478,000 trmk_TotalEstimatedFairValue / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember |  |
Gross unrealized losses [Abstract] |  |  |  |  |
Gross unrealized (losses), less than 12 months | (2,101,000)trmk_GrossUnrealizedLossesLessThan12Months / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | (52,000)trmk_GrossUnrealizedLossesLessThan12Months / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | (2,101,000)trmk_GrossUnrealizedLossesLessThan12Months / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember |  |
Gross unrealized (losses), 12 months or more | 0 trmk_GrossUnrealizedLosses12MonthsOrMore / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | (25,000)trmk_GrossUnrealizedLosses12MonthsOrMore / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | 0 trmk_GrossUnrealizedLosses12MonthsOrMore / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember |  |
Total gross unrealized (losses) | (2,101,000)trmk_TotalGrossUnrealizedLosses / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | (77,000)trmk_TotalGrossUnrealizedLosses / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | (2,101,000)trmk_TotalGrossUnrealizedLosses / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember |  |
Held to maturity, amortized cost [Abstract] |  |  |  |  |
Securities held to maturity (at amortized cost) | 100,159,000 us-gaap_HeldToMaturitySecurities / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | 100,971,000 us-gaap_HeldToMaturitySecurities / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | 100,159,000 us-gaap_HeldToMaturitySecurities / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember |  |
Held to maturity, estimated fair value [Abstract] |  |  |  |  |
Securities held to maturity (at fair value) | 98,579,000 us-gaap_HeldToMaturitySecuritiesFairValue / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | 103,602,000 us-gaap_HeldToMaturitySecuritiesFairValue / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | 98,579,000 us-gaap_HeldToMaturitySecuritiesFairValue / us-gaap_DebtSecurityAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember |  |
Obligations of States and Political Subdivisions [Member] |  |  |  |  |
Estimated fair value [Abstract] |  |  |  |  |
Estimated fair value, less than 12 months | 55,963,000 trmk_EstimatedFairValueLessThan12Months / us-gaap_DebtSecurityAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember | 8,431,000 trmk_EstimatedFairValueLessThan12Months / us-gaap_DebtSecurityAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember | 55,963,000 trmk_EstimatedFairValueLessThan12Months / us-gaap_DebtSecurityAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |  |
Estimated fair value, 12 months or more | 796,000 trmk_EstimatedFairValue12MonthsOrMore / us-gaap_DebtSecurityAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember | 3,800,000 trmk_EstimatedFairValue12MonthsOrMore / us-gaap_DebtSecurityAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember | 796,000 trmk_EstimatedFairValue12MonthsOrMore / us-gaap_DebtSecurityAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |  |
Total estimated fair value | 56,759,000 trmk_TotalEstimatedFairValue / us-gaap_DebtSecurityAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember | 12,231,000 trmk_TotalEstimatedFairValue / us-gaap_DebtSecurityAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember | 56,759,000 trmk_TotalEstimatedFairValue / us-gaap_DebtSecurityAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |  |
Gross unrealized losses [Abstract] |  |  |  |  |
Gross unrealized (losses), less than 12 months | (586,000)trmk_GrossUnrealizedLossesLessThan12Months / us-gaap_DebtSecurityAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember | (22,000)trmk_GrossUnrealizedLossesLessThan12Months / us-gaap_DebtSecurityAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember | (586,000)trmk_GrossUnrealizedLossesLessThan12Months / us-gaap_DebtSecurityAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |  |
Gross unrealized (losses), 12 months or more | (10,000)trmk_GrossUnrealizedLosses12MonthsOrMore / us-gaap_DebtSecurityAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember | (46,000)trmk_GrossUnrealizedLosses12MonthsOrMore / us-gaap_DebtSecurityAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember | (10,000)trmk_GrossUnrealizedLosses12MonthsOrMore / us-gaap_DebtSecurityAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |  |
Total gross unrealized (losses) | (596,000)trmk_TotalGrossUnrealizedLosses / us-gaap_DebtSecurityAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember | (68,000)trmk_TotalGrossUnrealizedLosses / us-gaap_DebtSecurityAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember | (596,000)trmk_TotalGrossUnrealizedLosses / us-gaap_DebtSecurityAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |  |
Held to maturity, amortized cost [Abstract] |  |  |  |  |
Securities held to maturity (at amortized cost) | 65,987,000 us-gaap_HeldToMaturitySecurities / us-gaap_DebtSecurityAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember | 63,505,000 us-gaap_HeldToMaturitySecurities / us-gaap_DebtSecurityAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember | 65,987,000 us-gaap_HeldToMaturitySecurities / us-gaap_DebtSecurityAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |  |
Held to maturity, estimated fair value [Abstract] |  |  |  |  |
Securities held to maturity (at fair value) | 68,512,000 us-gaap_HeldToMaturitySecuritiesFairValue / us-gaap_DebtSecurityAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember | 66,903,000 us-gaap_HeldToMaturitySecuritiesFairValue / us-gaap_DebtSecurityAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember | 68,512,000 us-gaap_HeldToMaturitySecuritiesFairValue / us-gaap_DebtSecurityAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |  |
Residential Mortgage Pass-Through Securities Guaranteed by GNMA [Member] |  |  |  |  |
Estimated fair value [Abstract] |  |  |  |  |
Estimated fair value, less than 12 months | 14,732,000 trmk_EstimatedFairValueLessThan12Months / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember | 7,199,000 trmk_EstimatedFairValueLessThan12Months / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember | 14,732,000 trmk_EstimatedFairValueLessThan12Months / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember |  |
Estimated fair value, 12 months or more | 161,000 trmk_EstimatedFairValue12MonthsOrMore / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember | 647,000 trmk_EstimatedFairValue12MonthsOrMore / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember | 161,000 trmk_EstimatedFairValue12MonthsOrMore / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember |  |
Total estimated fair value | 14,893,000 trmk_TotalEstimatedFairValue / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember | 7,846,000 trmk_TotalEstimatedFairValue / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember | 14,893,000 trmk_TotalEstimatedFairValue / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember |  |
Gross unrealized losses [Abstract] |  |  |  |  |
Gross unrealized (losses), less than 12 months | (155,000)trmk_GrossUnrealizedLossesLessThan12Months / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember | (22,000)trmk_GrossUnrealizedLossesLessThan12Months / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember | (155,000)trmk_GrossUnrealizedLossesLessThan12Months / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember |  |
Gross unrealized (losses), 12 months or more | (1,000)trmk_GrossUnrealizedLosses12MonthsOrMore / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember | (8,000)trmk_GrossUnrealizedLosses12MonthsOrMore / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember | (1,000)trmk_GrossUnrealizedLosses12MonthsOrMore / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember |  |
Total gross unrealized (losses) | (156,000)trmk_TotalGrossUnrealizedLosses / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember | (30,000)trmk_TotalGrossUnrealizedLosses / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember | (156,000)trmk_TotalGrossUnrealizedLosses / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember |  |
Held to maturity, amortized cost [Abstract] |  |  |  |  |
Securities held to maturity (at amortized cost) | 9,433,000 us-gaap_HeldToMaturitySecurities / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember | 19,115,000 us-gaap_HeldToMaturitySecurities / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember | 9,433,000 us-gaap_HeldToMaturitySecurities / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember |  |
Held to maturity, estimated fair value [Abstract] |  |  |  |  |
Securities held to maturity (at fair value) | 9,503,000 us-gaap_HeldToMaturitySecuritiesFairValue / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember | 19,565,000 us-gaap_HeldToMaturitySecuritiesFairValue / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember | 9,503,000 us-gaap_HeldToMaturitySecuritiesFairValue / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember |  |
Residential Mortgage Pass-Through Securities Issued by FNMA and FHLMC [Member] |  |  |  |  |
Estimated fair value [Abstract] |  |  |  |  |
Estimated fair value, less than 12 months | 118,466,000 trmk_EstimatedFairValueLessThan12Months / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesIssuedByFnmaAndFhlmcMember |  | 118,466,000 trmk_EstimatedFairValueLessThan12Months / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesIssuedByFnmaAndFhlmcMember |  |
Estimated fair value, 12 months or more | 0 trmk_EstimatedFairValue12MonthsOrMore / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesIssuedByFnmaAndFhlmcMember |  | 0 trmk_EstimatedFairValue12MonthsOrMore / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesIssuedByFnmaAndFhlmcMember |  |
Total estimated fair value | 118,466,000 trmk_TotalEstimatedFairValue / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesIssuedByFnmaAndFhlmcMember |  | 118,466,000 trmk_TotalEstimatedFairValue / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesIssuedByFnmaAndFhlmcMember |  |
Gross unrealized losses [Abstract] |  |  |  |  |
Gross unrealized (losses), less than 12 months | (2,071,000)trmk_GrossUnrealizedLossesLessThan12Months / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesIssuedByFnmaAndFhlmcMember |  | (2,071,000)trmk_GrossUnrealizedLossesLessThan12Months / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesIssuedByFnmaAndFhlmcMember |  |
Gross unrealized (losses), 12 months or more | 0 trmk_GrossUnrealizedLosses12MonthsOrMore / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesIssuedByFnmaAndFhlmcMember |  | 0 trmk_GrossUnrealizedLosses12MonthsOrMore / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesIssuedByFnmaAndFhlmcMember |  |
Total gross unrealized (losses) | (2,071,000)trmk_TotalGrossUnrealizedLosses / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesIssuedByFnmaAndFhlmcMember |  | (2,071,000)trmk_TotalGrossUnrealizedLosses / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesIssuedByFnmaAndFhlmcMember |  |
Held to maturity, amortized cost [Abstract] |  |  |  |  |
Securities held to maturity (at amortized cost) | 12,724,000 us-gaap_HeldToMaturitySecurities / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesIssuedByFnmaAndFhlmcMember | 11,437,000 us-gaap_HeldToMaturitySecurities / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesIssuedByFnmaAndFhlmcMember | 12,724,000 us-gaap_HeldToMaturitySecurities / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesIssuedByFnmaAndFhlmcMember |  |
Held to maturity, estimated fair value [Abstract] |  |  |  |  |
Securities held to maturity (at fair value) | 12,592,000 us-gaap_HeldToMaturitySecuritiesFairValue / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesIssuedByFnmaAndFhlmcMember | 11,908,000 us-gaap_HeldToMaturitySecuritiesFairValue / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesIssuedByFnmaAndFhlmcMember | 12,592,000 us-gaap_HeldToMaturitySecuritiesFairValue / us-gaap_DebtSecurityAxis = trmk_ResidentialMortgagePassThroughSecuritiesIssuedByFnmaAndFhlmcMember |  |
Other Residential Mortgage-Backed Securities Issued or Guaranteed by FNMA, FHLMC or GNMA [Member] |  |  |  |  |
Estimated fair value [Abstract] |  |  |  |  |
Estimated fair value, less than 12 months | 1,534,381,000 trmk_EstimatedFairValueLessThan12Months / us-gaap_DebtSecurityAxis = trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember | 537,033,000 trmk_EstimatedFairValueLessThan12Months / us-gaap_DebtSecurityAxis = trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember | 1,534,381,000 trmk_EstimatedFairValueLessThan12Months / us-gaap_DebtSecurityAxis = trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember |  |
Estimated fair value, 12 months or more | 23,458,000 trmk_EstimatedFairValue12MonthsOrMore / us-gaap_DebtSecurityAxis = trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember | 395,342,000 trmk_EstimatedFairValue12MonthsOrMore / us-gaap_DebtSecurityAxis = trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember | 23,458,000 trmk_EstimatedFairValue12MonthsOrMore / us-gaap_DebtSecurityAxis = trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember |  |
Total estimated fair value | 1,557,839,000 trmk_TotalEstimatedFairValue / us-gaap_DebtSecurityAxis = trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember | 932,375,000 trmk_TotalEstimatedFairValue / us-gaap_DebtSecurityAxis = trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember | 1,557,839,000 trmk_TotalEstimatedFairValue / us-gaap_DebtSecurityAxis = trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember |  |
Gross unrealized losses [Abstract] |  |  |  |  |
Gross unrealized (losses), less than 12 months | (36,750,000)trmk_GrossUnrealizedLossesLessThan12Months / us-gaap_DebtSecurityAxis = trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember | (2,449,000)trmk_GrossUnrealizedLossesLessThan12Months / us-gaap_DebtSecurityAxis = trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember | (36,750,000)trmk_GrossUnrealizedLossesLessThan12Months / us-gaap_DebtSecurityAxis = trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember |  |
Gross unrealized (losses), 12 months or more | (415,000)trmk_GrossUnrealizedLosses12MonthsOrMore / us-gaap_DebtSecurityAxis = trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember | (10,031,000)trmk_GrossUnrealizedLosses12MonthsOrMore / us-gaap_DebtSecurityAxis = trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember | (415,000)trmk_GrossUnrealizedLosses12MonthsOrMore / us-gaap_DebtSecurityAxis = trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember |  |
Total gross unrealized (losses) | (37,165,000)trmk_TotalGrossUnrealizedLosses / us-gaap_DebtSecurityAxis = trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember | (12,480,000)trmk_TotalGrossUnrealizedLosses / us-gaap_DebtSecurityAxis = trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember | (37,165,000)trmk_TotalGrossUnrealizedLosses / us-gaap_DebtSecurityAxis = trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember |  |
Held to maturity, amortized cost [Abstract] |  |  |  |  |
Securities held to maturity (at amortized cost) | 837,393,000 us-gaap_HeldToMaturitySecurities / us-gaap_DebtSecurityAxis = trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember | 834,176,000 us-gaap_HeldToMaturitySecurities / us-gaap_DebtSecurityAxis = trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember | 837,393,000 us-gaap_HeldToMaturitySecurities / us-gaap_DebtSecurityAxis = trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember |  |
Held to maturity, estimated fair value [Abstract] |  |  |  |  |
Securities held to maturity (at fair value) | 822,321,000 us-gaap_HeldToMaturitySecuritiesFairValue / us-gaap_DebtSecurityAxis = trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember | 838,700,000 us-gaap_HeldToMaturitySecuritiesFairValue / us-gaap_DebtSecurityAxis = trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember | 822,321,000 us-gaap_HeldToMaturitySecuritiesFairValue / us-gaap_DebtSecurityAxis = trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember |  |
Commercial Mortgage-Backed Securities Issued or Guaranteed by FNMA, FHLMC or GNMA [Member] |  |  |  |  |
Estimated fair value [Abstract] |  |  |  |  |
Estimated fair value, less than 12 months | 177,412,000 trmk_EstimatedFairValueLessThan12Months / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember | 9,134,000 trmk_EstimatedFairValueLessThan12Months / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember | 177,412,000 trmk_EstimatedFairValueLessThan12Months / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember |  |
Estimated fair value, 12 months or more | 0 trmk_EstimatedFairValue12MonthsOrMore / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember | 79,829,000 trmk_EstimatedFairValue12MonthsOrMore / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember | 0 trmk_EstimatedFairValue12MonthsOrMore / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember |  |
Total estimated fair value | 177,412,000 trmk_TotalEstimatedFairValue / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember | 88,963,000 trmk_TotalEstimatedFairValue / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember | 177,412,000 trmk_TotalEstimatedFairValue / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember |  |
Gross unrealized losses [Abstract] |  |  |  |  |
Gross unrealized (losses), less than 12 months | (4,214,000)trmk_GrossUnrealizedLossesLessThan12Months / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember | (3,000)trmk_GrossUnrealizedLossesLessThan12Months / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember | (4,214,000)trmk_GrossUnrealizedLossesLessThan12Months / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember |  |
Gross unrealized (losses), 12 months or more | 0 trmk_GrossUnrealizedLosses12MonthsOrMore / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember | (1,088,000)trmk_GrossUnrealizedLosses12MonthsOrMore / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember | 0 trmk_GrossUnrealizedLosses12MonthsOrMore / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember |  |
Total gross unrealized (losses) | (4,214,000)trmk_TotalGrossUnrealizedLosses / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember | (1,091,000)trmk_TotalGrossUnrealizedLosses / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember | (4,214,000)trmk_TotalGrossUnrealizedLosses / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember |  |
Held to maturity, amortized cost [Abstract] |  |  |  |  |
Securities held to maturity (at amortized cost) | 143,032,000 us-gaap_HeldToMaturitySecurities / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember | 141,481,000 us-gaap_HeldToMaturitySecurities / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember | 143,032,000 us-gaap_HeldToMaturitySecurities / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember |  |
Held to maturity, estimated fair value [Abstract] |  |  |  |  |
Securities held to maturity (at fair value) | 139,326,000 us-gaap_HeldToMaturitySecuritiesFairValue / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember | 142,168,000 us-gaap_HeldToMaturitySecuritiesFairValue / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember | 139,326,000 us-gaap_HeldToMaturitySecuritiesFairValue / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember |  |
Asset-Backed Securities and Structured Financial Products [Member] |  |  |  |  |
Held to maturity, amortized cost [Abstract] |  |  |  |  |
Securities held to maturity (at amortized cost) | 0 us-gaap_HeldToMaturitySecurities / us-gaap_DebtSecurityAxis = us-gaap_AssetBackedSecuritiesMember | 0 us-gaap_HeldToMaturitySecurities / us-gaap_DebtSecurityAxis = us-gaap_AssetBackedSecuritiesMember | 0 us-gaap_HeldToMaturitySecurities / us-gaap_DebtSecurityAxis = us-gaap_AssetBackedSecuritiesMember |  |
Held to maturity, estimated fair value [Abstract] |  |  |  |  |
Securities held to maturity (at fair value) | 0 us-gaap_HeldToMaturitySecuritiesFairValue / us-gaap_DebtSecurityAxis = us-gaap_AssetBackedSecuritiesMember | 0 us-gaap_HeldToMaturitySecuritiesFairValue / us-gaap_DebtSecurityAxis = us-gaap_AssetBackedSecuritiesMember | 0 us-gaap_HeldToMaturitySecuritiesFairValue / us-gaap_DebtSecurityAxis = us-gaap_AssetBackedSecuritiesMember |  |
Collateralized Loan Obligations [Member] |  |  |  |  |
Gross unrealized losses [Abstract] |  |  |  |  |
Sale of collateralized loan obligations | 135,600,000 us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt / us-gaap_DebtSecurityAxis = us-gaap_CollateralizedLoanObligationsMember |  |  |  |
Net gain on sale of collateralized loan obligations | 1,300,000 us-gaap_AvailableForSaleSecuritiesGrossRealizedGainLossNet / us-gaap_DebtSecurityAxis = us-gaap_CollateralizedLoanObligationsMember |  |  |  | 389,000 us-gaap_AvailableForSaleSecuritiesGrossRealizedGainLossNet / us-gaap_DebtSecurityAxis = us-gaap_CollateralizedLoanObligationsMember
Collateralized loan obligations sold during the first quarter of 2014 |  |  |  |  | $ 25,900,000 trmk_AvailableForSaleSecuritiesDebtSecuritiesSold / us-gaap_DebtSecurityAxis = us-gaap_CollateralizedLoanObligationsMember

X
- Definition Accumulated appreciation or loss, in value of the total of available-for-sale securities at the end of an accounting period. + References No definition available. + Details
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Balance Type: | credit
Period Type: | instant

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- Definition Amount of debt securities categorized neither as held-to-maturity nor trading and were sold during the first quarter of the reporting year. + References No definition available. + Details
Name: | trmk_AvailableForSaleSecuritiesDebtSecuritiesSold
Namespace Prefix: | trmk_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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- Definition This item represents the aggregate fair value of investments categorized as available-for-sale and held-to-maturity securities. that have been in a continuous unrealized loss position for twelve months or longer. + References No definition available. + Details
Name: | trmk_EstimatedFairValue12MonthsOrMore
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- Definition This item represents the aggregate fair value of investments categorized as available-for-sale and held-to-maturity securities. that have been in a continuous unrealized loss position for less than twelve months. + References No definition available. + Details
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- Definition This item represents the excess of amortized cost basis over fair value of securities that have been in a loss position for twelve months or longer for those securities which are categorized as available-for-sale and held-to-maturity securities. + References No definition available. + Details
Name: | trmk_GrossUnrealizedLosses12MonthsOrMore
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- Definition This item represents the excess of amortized cost basis over fair value of securities that have been in a loss position for less than twelve months for those securities which are categorized as available-for-sale and held-to-maturity securities. + References No definition available. + Details
Name: | trmk_GrossUnrealizedLossesLessThan12Months
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- Details
Name: | trmk_InvestmentsContinuousUnrealizedLossPositionAggregateLossesAbstract
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Balance Type: | na
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- Definition Amount before tax and reclassification adjustments of unrealized holding gain (loss) on available-for-sale securities at date of transfer. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Amount after tax, before reclassification adjustments, of unrealized holding gain (loss) on available-for-sale securities at date of transfer. + References No definition available. + Details
Name: | trmk_OtherComprehensiveIncomeLossUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTaxAtDateOfTransfer
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Data Type: | xbrli:monetaryItemType
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- Definition Securities pledged to collateralize agreements The carrying value as of the balance sheet date of securities pledged and securities that an institution sells and agrees to repurchase (the identical or substantially the same securities) as a seller-borrower at a specified date for a specified price, also known as a repurchase agreement, or repo. + References No definition available. + Details
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Namespace Prefix: | trmk_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Pledged securities to the discount window providing additional contingency funding to collateralize agreements. + References No definition available. + Details
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Namespace Prefix: | trmk_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition The cash inflow associated with the sale and calls of debt and equity securities classified as available-for-sale securities. + References No definition available. + Details
Name: | trmk_ProceedsFromCallsAndSalesOfSecurities
Namespace Prefix: | trmk_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition The cash inflow associated with the maturity calls (requests for early payments) of debt securities designated as held-to-maturity. + References No definition available. + Details
Name: | trmk_ProceedsFromMaturitiesCallsOfHeldToMaturitySecurities
Namespace Prefix: | trmk_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition This item represents the amount of securities categorized as available-for-sale being transferred to the held-to-maturity securities category. + References No definition available. + Details
Name: | trmk_ReclassificationOfAvailableForSaleToHeldToMaturitySecurities
Namespace Prefix: | trmk_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Total debt securities, excluding mortgage-back-securities, grouped by maturity dates, at cost, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments, as defined), and fair value hedge accounting adjustments, if any, which are classified neither as held-to-maturity nor trading securities. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Total investments in debt securities, excluding mortgage-back-securities, which are categorized as held-to-maturity. The held-to-maturity category is for those securities that the entity has the positive intent and ability to hold until maturity. + References No definition available. + Details
Name: | trmk_TotalAmortizedCostHeldToMaturityBeforeMortgageBackedSecurities
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Data Type: | xbrli:monetaryItemType
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- Definition This item represents the aggregate fair value of investments in an unrealized loss position which are categorized as available-for-sale and held-to-maturity securities. + References No definition available. + Details
Name: | trmk_TotalEstimatedFairValue
Namespace Prefix: | trmk_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Total investments in debt and equity securities, excluding mortgage-back-securities, which are categorized neither as held-to-maturity nor trading. + References No definition available. + Details
Name: | trmk_TotalFairValueOfAvailableForSaleSecuritiesBeforeMortgageBackSecurities
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- Definition Total debt securities, excluding mortgage-back-securities, grouped by maturity dates, at fair value, which are categorized as held-to-maturity. + References No definition available. + Details
Name: | trmk_TotalFairValueOfHeldToMaturitySecuritiesBeforeMortgageBackSecurities
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Balance Type: | debit
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- Definition This item represents the excess of amortized cost basis over fair value of securities in a loss position and which are categorized as available-for-sale and held-to-maturity securities. + References No definition available. + Details
Name: | trmk_TotalGrossUnrealizedLosses
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