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Significant Accounting Policies (Details) (USD $) Share data in Thousands, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2014 Factor Region Office | Dec. 31, 2013 | Dec. 31, 2012
Business [Abstract] |  |  |  |  |  |
Number of offices | 205 trmk_NumberOfOffices |  |  |  |  |
Loans Held-for-sale [Abstract] |  |  |  |  |  |
Percentage of remaining principal balance of the loan servicer may repurchase (in hundredths) | 100.00%trmk_PercentageOfRemainingPrincipalBalanceOfLoanServicerMayRepurchase |  |  |  |  |
Loans Held for Sale [Abstract] |  |  |  |  |  |
Number of days loan is contractually past due to be classified as a past due loan | 30 days |  |  |  |  |
Balance of commercial nonaccrual loans identified for impairment analysis, minimum | $ 500,000 trmk_BalanceOfCommercialLoansIdentifiedForImpairmentAnalysis |  |  |  |  |
Allowance for loan losses [Abstract] |  |  |  |  |  |
Methodology elements in allowance for loan losses guidance | 3 trmk_NumberOfElementsAllowanceForLoanLossesConsists |  |  |  |  |
Key market regions | 5 trmk_KeyMarketRegionsInQualitativeReserveAllocation |  |  |  |  |
Goodwill and Identifiable Intangible Assets [Abstract] |  |  |  |  |  |
Finite-lived intangible assets, average useful life | 20 years |  |  |  |  |
Federal Home Loan Bank and Federal Reserve stock |  |  |  |  |  |
Securities with limited marketability | 44,100,000 trmk_SecuritiesWithLimitedMarketability |  | 28,400,000 trmk_SecuritiesWithLimitedMarketability |  |  |
Statement of cash flows specific transaction amounts [Abstract] |  |  |  |  |  |
Income taxes paid | 13,710,000 us-gaap_IncomeTaxesPaid |  | 14,520,000 us-gaap_IncomeTaxesPaid |  | 57,834,000 us-gaap_IncomeTaxesPaid |
Interest expense paid on deposits and borrowings | 22,268,000 us-gaap_InterestPaid |  | 25,715,000 us-gaap_InterestPaid |  | 31,496,000 us-gaap_InterestPaid |
Noncash transfers from loans to foreclosed properties | 39,778,000 trmk_NoncashTransfersFromLoansToForeclosedProperties | [1] | 41,042,000 trmk_NoncashTransfersFromLoansToForeclosedProperties | [1] | 37,635,000 trmk_NoncashTransfersFromLoansToForeclosedProperties | [1]
Transfer of long-term FHLB advances to short-term | 6,644,000 trmk_TransferOfLongTermFhlbAdvanceToShortTerm |  | 0 trmk_TransferOfLongTermFhlbAdvanceToShortTerm |  | 0 trmk_TransferOfLongTermFhlbAdvanceToShortTerm |
Assets acquired in business combination | 0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets |  | 1,845,543,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets |  | 234,960,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets |
Liabilities assumed in business combination | 0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities |  | 1,821,066,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities |  | 209,322,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities |
Statement [Line Items] |  |  |  |  |  |
Net cash provided by operating activities | 211,267,000 us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations |  | 301,183,000 us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations |  | 112,277,000 us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations |
Net cash provided by (used in) investing activities | (556,255,000)us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations |  | (258,967,000)us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations |  | 173,739,000 us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations |
Net cash provided by (used in) financing activities | 315,200,000 us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperations |  | 72,056,000 us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperations |  | (257,152,000)us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperations |
(Decrease) increase in cash and cash equivalents | (29,788,000)us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease |  | 114,272,000 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease |  | 28,864,000 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease |
Cash and cash equivalents at beginning of year | 345,761,000 us-gaap_CashAndCashEquivalentsAtCarryingValue |  | 231,489,000 us-gaap_CashAndCashEquivalentsAtCarryingValue |  | 202,625,000 us-gaap_CashAndCashEquivalentsAtCarryingValue |
Cash and cash equivalents at end of year | 315,973,000 us-gaap_CashAndCashEquivalentsAtCarryingValue |  | 345,761,000 us-gaap_CashAndCashEquivalentsAtCarryingValue |  | 231,489,000 us-gaap_CashAndCashEquivalentsAtCarryingValue |
Weighted-average shares used to calculate basic and diluted EPS [Abstract] |  |  |  |  |  |
Basic shares (in shares) | 67,434 us-gaap_WeightedAverageNumberOfSharesOutstandingBasic |  | 66,897 us-gaap_WeightedAverageNumberOfSharesOutstandingBasic |  | 64,659 us-gaap_WeightedAverageNumberOfSharesOutstandingBasic |
Dilutive shares (in shares) | 160 us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment |  | 176 us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment |  | 192 us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment |
Diluted shares (in shares) | 67,594 us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding |  | 67,073 us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding |  | 64,851 us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding |
Weighted-average antidilutive stock awards (in shares) | 32 us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount |  | 333 us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount |  | 653 us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount |
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] |  |  |  |  |  |
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items] |  |  |  |  |  |
Variable interest rate, description | three-month LIBOR |  |  |  |  |
Period for which cash flow hedges will be used to hedge quarterly interest payments | 5 years |  |  |  |  |
As Reported [Member] |  |  |  |  |  |
Statement [Line Items] |  |  |  |  |  |
Net cash provided by operating activities |  |  | 155,417,000 us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations / us-gaap_StatementScenarioAxis = us-gaap_ScenarioPreviouslyReportedMember |  | 92,125,000 us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations / us-gaap_StatementScenarioAxis = us-gaap_ScenarioPreviouslyReportedMember |
Net cash provided by (used in) investing activities |  |  | (113,201,000)us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations / us-gaap_StatementScenarioAxis = us-gaap_ScenarioPreviouslyReportedMember |  | 193,891,000 us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations / us-gaap_StatementScenarioAxis = us-gaap_ScenarioPreviouslyReportedMember |
Net cash provided by (used in) financing activities |  |  | 72,056,000 us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperations / us-gaap_StatementScenarioAxis = us-gaap_ScenarioPreviouslyReportedMember |  | (257,152,000)us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperations / us-gaap_StatementScenarioAxis = us-gaap_ScenarioPreviouslyReportedMember |
(Decrease) increase in cash and cash equivalents |  |  | 114,272,000 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease / us-gaap_StatementScenarioAxis = us-gaap_ScenarioPreviouslyReportedMember |  | 28,864,000 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease / us-gaap_StatementScenarioAxis = us-gaap_ScenarioPreviouslyReportedMember |
Cash and cash equivalents at beginning of year |  |  | 231,489,000 us-gaap_CashAndCashEquivalentsAtCarryingValue / us-gaap_StatementScenarioAxis = us-gaap_ScenarioPreviouslyReportedMember |  | 202,625,000 us-gaap_CashAndCashEquivalentsAtCarryingValue / us-gaap_StatementScenarioAxis = us-gaap_ScenarioPreviouslyReportedMember |
Cash and cash equivalents at end of year |  |  | 345,761,000 us-gaap_CashAndCashEquivalentsAtCarryingValue / us-gaap_StatementScenarioAxis = us-gaap_ScenarioPreviouslyReportedMember |  | 231,489,000 us-gaap_CashAndCashEquivalentsAtCarryingValue / us-gaap_StatementScenarioAxis = us-gaap_ScenarioPreviouslyReportedMember |
Adjustment [Member] |  |  |  |  |  |
Statement [Line Items] |  |  |  |  |  |
Net cash provided by operating activities |  |  | 145,766,000 us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations / us-gaap_StatementScenarioAxis = us-gaap_ScenarioAdjustmentMember |  | 20,152,000 us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations / us-gaap_StatementScenarioAxis = us-gaap_ScenarioAdjustmentMember |
Net cash provided by (used in) investing activities |  |  | (145,766,000)us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations / us-gaap_StatementScenarioAxis = us-gaap_ScenarioAdjustmentMember |  | (20,152,000)us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations / us-gaap_StatementScenarioAxis = us-gaap_ScenarioAdjustmentMember |
Net cash provided by (used in) financing activities |  |  | 0 us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperations / us-gaap_StatementScenarioAxis = us-gaap_ScenarioAdjustmentMember |  | 0 us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperations / us-gaap_StatementScenarioAxis = us-gaap_ScenarioAdjustmentMember |
(Decrease) increase in cash and cash equivalents |  |  | 0 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease / us-gaap_StatementScenarioAxis = us-gaap_ScenarioAdjustmentMember |  | 0 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease / us-gaap_StatementScenarioAxis = us-gaap_ScenarioAdjustmentMember |
Cash and cash equivalents at beginning of year |  |  | 0 us-gaap_CashAndCashEquivalentsAtCarryingValue / us-gaap_StatementScenarioAxis = us-gaap_ScenarioAdjustmentMember |  | 0 us-gaap_CashAndCashEquivalentsAtCarryingValue / us-gaap_StatementScenarioAxis = us-gaap_ScenarioAdjustmentMember |
Cash and cash equivalents at end of year |  |  | $ 0 us-gaap_CashAndCashEquivalentsAtCarryingValue / us-gaap_StatementScenarioAxis = us-gaap_ScenarioAdjustmentMember |  | $ 0 us-gaap_CashAndCashEquivalentsAtCarryingValue / us-gaap_StatementScenarioAxis = us-gaap_ScenarioAdjustmentMember |
Maximum [Member] |  |  |  |  |  |
Loans Held for Sale [Abstract] |  |  |  |  |  |
Number of days mortgage LHFS are retained on Trustmark's balance sheet | 45 days |  |  |  |  |
Maximum [Member] | Buildings [Member] |  |  |  |  |  |
Premises and Equipment, Net [Abstract] |  |  |  |  |  |
Estimated useful lives of the assets | 39 years |  |  |  |  |
Maximum [Member] | Furniture and Equipment [Member] |  |  |  |  |  |
Premises and Equipment, Net [Abstract] |  |  |  |  |  |
Estimated useful lives of the assets | 10 years |  |  |  |  |
Minimum [Member] |  |  |  |  |  |
Loans Held for Sale [Abstract] |  |  |  |  |  |
Number of days mortgage LHFS are retained on Trustmark's balance sheet | 30 days |  |  |  |  |
Minimum [Member] | Furniture and Equipment [Member] |  |  |  |  |  |
Premises and Equipment, Net [Abstract] |  |  |  |  |  |
Estimated useful lives of the assets | 3 years |  |  |  |  |
Commercial Credits [Member] |  |  |  |  |  |
Loans Held for Investment [Abstract] |  |  |  |  |  |
Number of days past due on credits for loan to be classified as nonaccrual | 90 days |  |  |  |  |
Non-Business Purpose Credits [Member] |  |  |  |  |  |
Loans Held for Investment [Abstract] |  |  |  |  |  |
Number of days past due on credits for loan to be classified as nonaccrual | 120 days |  |  |  |  |
Consumer Loans [Member] |  |  |  |  |  |
Loans Held for Investment [Abstract] |  |  |  |  |  |
Number of days past due loans are generally charged-off | 180 days |  |  |  |  |
Non-real Estate Consumer Purpose Loans [Member] |  |  |  |  |  |
Loans Held for Investment [Abstract] |  |  |  |  |  |
Number of days past due loans are generally charged-off | 120 days |  |  |  |  |
Credit Card Loans [Member] |  |  |  |  |  |
Loans Held for Investment [Abstract] |  |  |  |  |  |
Number of days past due loans are generally charged-off | 180 days |  |  |  |  |
[1] | Includes transfers from covered loans to foreclosed properties.

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