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Securities Available for Sale and Held to Maturity (1) (Details) (USD $)
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2013
Dec. 31, 2014
Estimated Fair Value [Abstract]        
Estimated Fair Value, Less than 12 Months $ 129,154,000trmk_EstimatedFairValueLessThan12Months     $ 590,965,000trmk_EstimatedFairValueLessThan12Months
Estimated Fair Value, 12 Months or More 336,516,000trmk_EstimatedFairValue12MonthsOrMore     522,230,000trmk_EstimatedFairValue12MonthsOrMore
Estimated Fair Value, Total 465,670,000trmk_TotalEstimatedFairValue     1,113,195,000trmk_TotalEstimatedFairValue
Gross Unrealized (Losses) [Abstract]        
Gross Unrealized (Losses), Less than 12 Months (686,000)trmk_GrossUnrealizedLossesLessThan12Months     (2,663,000)trmk_GrossUnrealizedLossesLessThan12Months
Gross Unrealized (Losses), 12 Months or More (5,205,000)trmk_GrossUnrealizedLosses12MonthsOrMore     (11,909,000)trmk_GrossUnrealizedLosses12MonthsOrMore
Gross Unrealized (Losses), Total (5,891,000)trmk_TotalGrossUnrealizedLosses     (14,572,000)trmk_TotalGrossUnrealizedLosses
Reclassification of Securities available for sale to securities held to maturity     1,099,000,000trmk_ReclassificationOfAvailableForSaleToHeldToMaturitySecurities  
Net unrealized holding loss on AFS Securities at date of transfer     46,600,000trmk_OtherComprehensiveIncomeLossUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTaxAtDateOfTransfer  
Net unrealized holding loss on AFS Securities, net of tax at date of transfer     28,800,000trmk_OtherComprehensiveIncomeLossUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTaxAtDateOfTransfer  
Net unamortized, unrealized loss on transfer of securities 39,000,000trmk_AccumulatedOtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustment      
Net unamortized, unrealized loss on transfer of securities, net of tax 24,100,000us-gaap_AccumulatedOtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax      
Gain (Loss) on Investments [Line Items]        
Other-than-temporary impairments 0us-gaap_ImpairmentOfInvestments 0us-gaap_ImpairmentOfInvestments    
Securities Available for Sale, Amortized Cost [Abstract]        
Due in one year or less 18,840,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost      
Due after one year through five years 136,818,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost      
Due after five years through ten years 58,712,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost      
Due after ten years 80,013,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost      
Total amortized cost, before mortgage-backed securities 294,383,000trmk_TotalAmortizedCostBeforeMortgageBackedSecurities      
Mortgage-backed securities 2,046,084,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateAmortizedCost      
Securities available for sale (at amortized cost) 2,340,467,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCost      
Securities Available for Sale, Estimated Fair Value [Abstract]        
Due in one year or less 18,955,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue      
Due after one year through five years 141,195,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue      
Due after five years through ten years 61,041,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue      
Due after ten years 80,252,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue      
Total fair value, before mortgage-backed securities 301,443,000trmk_TotalFairValueOfAvailableForSaleSecuritiesBeforeMortgageBackSecurities      
Mortgage-backed securities 2,080,016,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue      
Securities available for sale (at fair value) 2,381,459,000us-gaap_AvailableForSaleSecurities     2,374,567,000us-gaap_AvailableForSaleSecurities
Securities Held to Maturity, Amortized Cost [Abstract]        
Due in one year or less 2,441,000us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearNetCarryingAmount      
Due after one year through five years 11,818,000us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterOneThroughFiveYearsNetCarryingAmount      
Due after five years through ten years 137,514,000us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterFiveThroughTenYearsNetCarryingAmount      
Due after ten years 12,326,000us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterTenYearsNetCarryingAmount      
Total, amortized cost, before mortgage-backed securities 164,099,000trmk_TotalAmortizedCostHeldToMaturityBeforeMortgageBackedSecurities      
Mortgage-backed securities 1,020,455,000us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithoutSingleMaturityDateNetCarryingAmount      
Securities held to maturity (at amortized cost) 1,184,554,000us-gaap_HeldToMaturitySecurities     1,170,685,000us-gaap_HeldToMaturitySecurities
Securities Held to Maturity, Estimated Fair Value [Abstract]        
Due in one year or less 2,460,000us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearFairValue      
Due after one year through five years 12,345,000us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue      
Due after five years through ten years 144,041,000us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue      
Due after ten years 13,350,000us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterTenYearsFairValue      
Total fair value, before mortgage-backed securities 172,196,000trmk_TotalFairValueOfHeldToMaturitySecuritiesBeforeMortgageBackSecurities      
Mortgage-backed securities 1,040,309,000us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue      
Securities held to maturity (at fair value) 1,212,505,000us-gaap_HeldToMaturitySecuritiesFairValue     1,182,846,000us-gaap_HeldToMaturitySecuritiesFairValue
Available for Sale [Member]        
Gains (losses) on Investments [Abstract]        
Proceeds from calls and sales of securities 0trmk_ProceedsFromCallsAndSalesOfSecurities
/ us-gaap_GainLossOnInvestmentsByCategoryAxis
= us-gaap_AvailableforsaleSecuritiesMember		 26,274,000trmk_ProceedsFromCallsAndSalesOfSecurities
/ us-gaap_GainLossOnInvestmentsByCategoryAxis
= us-gaap_AvailableforsaleSecuritiesMember		    
Gross realized gains 0us-gaap_AvailableForSaleSecuritiesGrossRealizedGains
/ us-gaap_GainLossOnInvestmentsByCategoryAxis
= us-gaap_AvailableforsaleSecuritiesMember		 389,000us-gaap_AvailableForSaleSecuritiesGrossRealizedGains
/ us-gaap_GainLossOnInvestmentsByCategoryAxis
= us-gaap_AvailableforsaleSecuritiesMember		    
U.S. Government Agency Obligations Issued by U.S. Government Agencies [Member]        
Estimated Fair Value [Abstract]        
Estimated Fair Value, Less than 12 Months 0trmk_EstimatedFairValueLessThan12Months
/ us-gaap_DebtSecurityAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember		     19,220,000trmk_EstimatedFairValueLessThan12Months
/ us-gaap_DebtSecurityAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Estimated Fair Value, 12 Months or More 34,542,000trmk_EstimatedFairValue12MonthsOrMore
/ us-gaap_DebtSecurityAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember		     32,656,000trmk_EstimatedFairValue12MonthsOrMore
/ us-gaap_DebtSecurityAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Estimated Fair Value, Total 34,542,000trmk_TotalEstimatedFairValue
/ us-gaap_DebtSecurityAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember		     51,876,000trmk_TotalEstimatedFairValue
/ us-gaap_DebtSecurityAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Gross Unrealized (Losses) [Abstract]        
Gross Unrealized (Losses), Less than 12 Months 0trmk_GrossUnrealizedLossesLessThan12Months
/ us-gaap_DebtSecurityAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember		     (115,000)trmk_GrossUnrealizedLossesLessThan12Months
/ us-gaap_DebtSecurityAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Gross Unrealized (Losses), 12 Months or More (557,000)trmk_GrossUnrealizedLosses12MonthsOrMore
/ us-gaap_DebtSecurityAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember		     (711,000)trmk_GrossUnrealizedLosses12MonthsOrMore
/ us-gaap_DebtSecurityAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Gross Unrealized (Losses), Total (557,000)trmk_TotalGrossUnrealizedLosses
/ us-gaap_DebtSecurityAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember		     (826,000)trmk_TotalGrossUnrealizedLosses
/ us-gaap_DebtSecurityAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Securities Held to Maturity, Amortized Cost [Abstract]        
Securities held to maturity (at amortized cost) 0us-gaap_HeldToMaturitySecurities
/ us-gaap_DebtSecurityAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember		     0us-gaap_HeldToMaturitySecurities
/ us-gaap_DebtSecurityAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Securities Held to Maturity, Estimated Fair Value [Abstract]        
Securities held to maturity (at fair value) 0us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_DebtSecurityAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember		     0us-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       9,948,000trmk_EstimatedFairValueLessThan12Months
/ us-gaap_DebtSecurityAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Estimated Fair Value, 12 Months or More       9,956,000trmk_EstimatedFairValue12MonthsOrMore
/ us-gaap_DebtSecurityAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Estimated Fair Value, Total       19,904,000trmk_TotalEstimatedFairValue
/ us-gaap_DebtSecurityAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Gross Unrealized (Losses) [Abstract]        
Gross Unrealized (Losses), Less than 12 Months       (52,000)trmk_GrossUnrealizedLossesLessThan12Months
/ us-gaap_DebtSecurityAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Gross Unrealized (Losses), 12 Months or More       (25,000)trmk_GrossUnrealizedLosses12MonthsOrMore
/ us-gaap_DebtSecurityAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Gross Unrealized (Losses), Total       (77,000)trmk_TotalGrossUnrealizedLosses
/ us-gaap_DebtSecurityAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Securities Held to Maturity, Amortized Cost [Abstract]        
Securities held to maturity (at amortized cost) 101,171,000us-gaap_HeldToMaturitySecurities
/ us-gaap_DebtSecurityAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember		     100,971,000us-gaap_HeldToMaturitySecurities
/ us-gaap_DebtSecurityAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Securities Held to Maturity, Estimated Fair Value [Abstract]        
Securities held to maturity (at fair value) 105,529,000us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_DebtSecurityAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember		     103,602,000us-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 2,359,000trmk_EstimatedFairValueLessThan12Months
/ us-gaap_DebtSecurityAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		     8,431,000trmk_EstimatedFairValueLessThan12Months
/ us-gaap_DebtSecurityAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Estimated Fair Value, 12 Months or More 2,861,000trmk_EstimatedFairValue12MonthsOrMore
/ us-gaap_DebtSecurityAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		     3,800,000trmk_EstimatedFairValue12MonthsOrMore
/ us-gaap_DebtSecurityAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Estimated Fair Value, Total 5,220,000trmk_TotalEstimatedFairValue
/ us-gaap_DebtSecurityAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		     12,231,000trmk_TotalEstimatedFairValue
/ us-gaap_DebtSecurityAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Gross Unrealized (Losses) [Abstract]        
Gross Unrealized (Losses), Less than 12 Months (9,000)trmk_GrossUnrealizedLossesLessThan12Months
/ us-gaap_DebtSecurityAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		     (22,000)trmk_GrossUnrealizedLossesLessThan12Months
/ us-gaap_DebtSecurityAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Gross Unrealized (Losses), 12 Months or More (23,000)trmk_GrossUnrealizedLosses12MonthsOrMore
/ us-gaap_DebtSecurityAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		     (46,000)trmk_GrossUnrealizedLosses12MonthsOrMore
/ us-gaap_DebtSecurityAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Gross Unrealized (Losses), Total (32,000)trmk_TotalGrossUnrealizedLosses
/ us-gaap_DebtSecurityAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		     (68,000)trmk_TotalGrossUnrealizedLosses
/ us-gaap_DebtSecurityAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Securities Held to Maturity, Amortized Cost [Abstract]        
Securities held to maturity (at amortized cost) 62,928,000us-gaap_HeldToMaturitySecurities
/ us-gaap_DebtSecurityAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		     63,505,000us-gaap_HeldToMaturitySecurities
/ us-gaap_DebtSecurityAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Securities Held to Maturity, Estimated Fair Value [Abstract]        
Securities held to maturity (at fair value) 66,667,000us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_DebtSecurityAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		     66,903,000us-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 5,407,000trmk_EstimatedFairValueLessThan12Months
/ us-gaap_DebtSecurityAxis
= trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember		     7,199,000trmk_EstimatedFairValueLessThan12Months
/ us-gaap_DebtSecurityAxis
= trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember
Estimated Fair Value, 12 Months or More 0trmk_EstimatedFairValue12MonthsOrMore
/ us-gaap_DebtSecurityAxis
= trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember		     647,000trmk_EstimatedFairValue12MonthsOrMore
/ us-gaap_DebtSecurityAxis
= trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember
Estimated Fair Value, Total 5,407,000trmk_TotalEstimatedFairValue
/ us-gaap_DebtSecurityAxis
= trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember		     7,846,000trmk_TotalEstimatedFairValue
/ us-gaap_DebtSecurityAxis
= trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember
Gross Unrealized (Losses) [Abstract]        
Gross Unrealized (Losses), Less than 12 Months (12,000)trmk_GrossUnrealizedLossesLessThan12Months
/ us-gaap_DebtSecurityAxis
= trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember		     (22,000)trmk_GrossUnrealizedLossesLessThan12Months
/ us-gaap_DebtSecurityAxis
= trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember
Gross Unrealized (Losses), 12 Months or More 0trmk_GrossUnrealizedLosses12MonthsOrMore
/ us-gaap_DebtSecurityAxis
= trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember		     (8,000)trmk_GrossUnrealizedLosses12MonthsOrMore
/ us-gaap_DebtSecurityAxis
= trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember
Gross Unrealized (Losses), Total (12,000)trmk_TotalGrossUnrealizedLosses
/ us-gaap_DebtSecurityAxis
= trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember		     (30,000)trmk_TotalGrossUnrealizedLosses
/ us-gaap_DebtSecurityAxis
= trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember
Securities Held to Maturity, Amortized Cost [Abstract]        
Securities held to maturity (at amortized cost) 18,861,000us-gaap_HeldToMaturitySecurities
/ us-gaap_DebtSecurityAxis
= trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember		     19,115,000us-gaap_HeldToMaturitySecurities
/ us-gaap_DebtSecurityAxis
= trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember
Securities Held to Maturity, Estimated Fair Value [Abstract]        
Securities held to maturity (at fair value) 19,403,000us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_DebtSecurityAxis
= trmk_ResidentialMortgagePassThroughSecuritiesGuaranteedByGnmaMember		     19,565,000us-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 27,000trmk_EstimatedFairValueLessThan12Months
/ us-gaap_DebtSecurityAxis
= trmk_ResidentialMortgagePassThroughSecuritiesIssuedByFnmaAndFhlmcMember		      
Estimated Fair Value, 12 Months or More 0trmk_EstimatedFairValue12MonthsOrMore
/ us-gaap_DebtSecurityAxis
= trmk_ResidentialMortgagePassThroughSecuritiesIssuedByFnmaAndFhlmcMember		      
Estimated Fair Value, Total 27,000trmk_TotalEstimatedFairValue
/ us-gaap_DebtSecurityAxis
= trmk_ResidentialMortgagePassThroughSecuritiesIssuedByFnmaAndFhlmcMember		      
Gross Unrealized (Losses) [Abstract]        
Gross Unrealized (Losses), Less than 12 Months (1,000)trmk_GrossUnrealizedLossesLessThan12Months
/ us-gaap_DebtSecurityAxis
= trmk_ResidentialMortgagePassThroughSecuritiesIssuedByFnmaAndFhlmcMember		      
Gross Unrealized (Losses), 12 Months or More 0trmk_GrossUnrealizedLosses12MonthsOrMore
/ us-gaap_DebtSecurityAxis
= trmk_ResidentialMortgagePassThroughSecuritiesIssuedByFnmaAndFhlmcMember		      
Gross Unrealized (Losses), Total (1,000)trmk_TotalGrossUnrealizedLosses
/ us-gaap_DebtSecurityAxis
= trmk_ResidentialMortgagePassThroughSecuritiesIssuedByFnmaAndFhlmcMember		      
Securities Held to Maturity, Amortized Cost [Abstract]        
Securities held to maturity (at amortized cost) 11,341,000us-gaap_HeldToMaturitySecurities
/ us-gaap_DebtSecurityAxis
= trmk_ResidentialMortgagePassThroughSecuritiesIssuedByFnmaAndFhlmcMember		     11,437,000us-gaap_HeldToMaturitySecurities
/ us-gaap_DebtSecurityAxis
= trmk_ResidentialMortgagePassThroughSecuritiesIssuedByFnmaAndFhlmcMember
Securities Held to Maturity, Estimated Fair Value [Abstract]        
Securities held to maturity (at fair value) 11,919,000us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_DebtSecurityAxis
= trmk_ResidentialMortgagePassThroughSecuritiesIssuedByFnmaAndFhlmcMember		     11,908,000us-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 114,658,000trmk_EstimatedFairValueLessThan12Months
/ us-gaap_DebtSecurityAxis
= trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember		     537,033,000trmk_EstimatedFairValueLessThan12Months
/ us-gaap_DebtSecurityAxis
= trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember
Estimated Fair Value, 12 Months or More 272,760,000trmk_EstimatedFairValue12MonthsOrMore
/ us-gaap_DebtSecurityAxis
= trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember		     395,342,000trmk_EstimatedFairValue12MonthsOrMore
/ us-gaap_DebtSecurityAxis
= trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember
Estimated Fair Value, Total 387,418,000trmk_TotalEstimatedFairValue
/ us-gaap_DebtSecurityAxis
= trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember		     932,375,000trmk_TotalEstimatedFairValue
/ us-gaap_DebtSecurityAxis
= trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember
Gross Unrealized (Losses) [Abstract]        
Gross Unrealized (Losses), Less than 12 Months (634,000)trmk_GrossUnrealizedLossesLessThan12Months
/ us-gaap_DebtSecurityAxis
= trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember		     (2,449,000)trmk_GrossUnrealizedLossesLessThan12Months
/ us-gaap_DebtSecurityAxis
= trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember
Gross Unrealized (Losses), 12 Months or More (4,566,000)trmk_GrossUnrealizedLosses12MonthsOrMore
/ us-gaap_DebtSecurityAxis
= trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember		     (10,031,000)trmk_GrossUnrealizedLosses12MonthsOrMore
/ us-gaap_DebtSecurityAxis
= trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember
Gross Unrealized (Losses), Total (5,200,000)trmk_TotalGrossUnrealizedLosses
/ us-gaap_DebtSecurityAxis
= trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember		     (12,480,000)trmk_TotalGrossUnrealizedLosses
/ us-gaap_DebtSecurityAxis
= trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember
Securities Held to Maturity, Amortized Cost [Abstract]        
Securities held to maturity (at amortized cost) 842,827,000us-gaap_HeldToMaturitySecurities
/ us-gaap_DebtSecurityAxis
= trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember		     834,176,000us-gaap_HeldToMaturitySecurities
/ us-gaap_DebtSecurityAxis
= trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember
Securities Held to Maturity, Estimated Fair Value [Abstract]        
Securities held to maturity (at fair value) 858,460,000us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_DebtSecurityAxis
= trmk_OtherResidentialMortgageBackedSecuritiesIssuedOrGuaranteedByFnmaFhlmcOrGnmaMember		     838,700,000us-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 6,703,000trmk_EstimatedFairValueLessThan12Months
/ us-gaap_DebtSecurityAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember		     9,134,000trmk_EstimatedFairValueLessThan12Months
/ us-gaap_DebtSecurityAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
Estimated Fair Value, 12 Months or More 26,353,000trmk_EstimatedFairValue12MonthsOrMore
/ us-gaap_DebtSecurityAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember		     79,829,000trmk_EstimatedFairValue12MonthsOrMore
/ us-gaap_DebtSecurityAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
Estimated Fair Value, Total 33,056,000trmk_TotalEstimatedFairValue
/ us-gaap_DebtSecurityAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember		     88,963,000trmk_TotalEstimatedFairValue
/ us-gaap_DebtSecurityAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
Gross Unrealized (Losses) [Abstract]        
Gross Unrealized (Losses), Less than 12 Months (30,000)trmk_GrossUnrealizedLossesLessThan12Months
/ us-gaap_DebtSecurityAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember		     (3,000)trmk_GrossUnrealizedLossesLessThan12Months
/ us-gaap_DebtSecurityAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
Gross Unrealized (Losses), 12 Months or More (59,000)trmk_GrossUnrealizedLosses12MonthsOrMore
/ us-gaap_DebtSecurityAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember		     (1,088,000)trmk_GrossUnrealizedLosses12MonthsOrMore
/ us-gaap_DebtSecurityAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
Gross Unrealized (Losses), Total (89,000)trmk_TotalGrossUnrealizedLosses
/ us-gaap_DebtSecurityAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember		     (1,091,000)trmk_TotalGrossUnrealizedLosses
/ us-gaap_DebtSecurityAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
Securities Held to Maturity, Amortized Cost [Abstract]        
Securities held to maturity (at amortized cost) 147,426,000us-gaap_HeldToMaturitySecurities
/ us-gaap_DebtSecurityAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember		     141,481,000us-gaap_HeldToMaturitySecurities
/ us-gaap_DebtSecurityAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
Securities Held to Maturity, Estimated Fair Value [Abstract]        
Securities held to maturity (at fair value) 150,527,000us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_DebtSecurityAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember		     142,168,000us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_DebtSecurityAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
Asset-Backed Securities and Structured Financial Products [Member]        
Securities Held to Maturity, Amortized Cost [Abstract]        
Securities held to maturity (at amortized cost) 0us-gaap_HeldToMaturitySecurities
/ us-gaap_DebtSecurityAxis
= us-gaap_AssetBackedSecuritiesMember		     0us-gaap_HeldToMaturitySecurities
/ us-gaap_DebtSecurityAxis
= us-gaap_AssetBackedSecuritiesMember
Securities Held to Maturity, Estimated Fair Value [Abstract]        
Securities held to maturity (at fair value) $ 0us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_DebtSecurityAxis
= us-gaap_AssetBackedSecuritiesMember		     $ 0us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_DebtSecurityAxis
= us-gaap_AssetBackedSecuritiesMember