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Goodwill and Identifiable Intangible Assets (Details) (USD $) | 12 Months Ended
--- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Goodwill [Roll Forward] |  |  |
Goodwill, beginning of period | $ 372,851,000 us-gaap_Goodwill | $ 291,104,000 us-gaap_Goodwill |
Goodwill from acquisitions |  | 81,747,000 us-gaap_GoodwillAcquiredDuringPeriod |
Measurement period adjustment during 2014 | (7,351,000)us-gaap_GoodwillImpairedAdjustmentToInitialEstimateAmount |  |
Balance, end of period | 365,500,000 us-gaap_Goodwill | 372,851,000 us-gaap_Goodwill | 291,104,000 us-gaap_Goodwill
Finite-Lived Intangible Assets [Line Items] |  |  |
Gross Carrying Amount | 99,532,000 us-gaap_FiniteLivedIntangibleAssetsGross | 99,532,000 us-gaap_FiniteLivedIntangibleAssetsGross |
Accumulated Amortization | 66,298,000 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization | 57,542,000 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization |
Net Carrying Amount | 33,234,000 us-gaap_IntangibleAssetsNetExcludingGoodwill | 41,990,000 us-gaap_IntangibleAssetsNetExcludingGoodwill |
Remaining Weighted-Average Amortization Period in Years | 7 years 4 months 24 days |  |
Amortization expense of identifiable intangible assets | 8,800,000 us-gaap_AmortizationOfIntangibleAssets | 8,800,000 us-gaap_AmortizationOfIntangibleAssets | 3,800,000 us-gaap_AmortizationOfIntangibleAssets
Future amortization expense for identifiable intangible assets [Abstract] |  |  |
2015 | 7,600,000 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths |  |
2016 | 6,700,000 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo |  |
2017 | 5,700,000 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree |  |
2018 | 4,800,000 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour |  |
2019 | 3,600,000 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive |  |
Impairment losses on identifiable intangible assets | 0 us-gaap_ImpairmentOfIntangibleAssetsFinitelived | 0 us-gaap_ImpairmentOfIntangibleAssetsFinitelived | 0 us-gaap_ImpairmentOfIntangibleAssetsFinitelived
Core Deposit Intangibles [Member] |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |
Gross Carrying Amount | 85,824,000 us-gaap_FiniteLivedIntangibleAssetsGross / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = trmk_CoreDepositIntangiblesMember | 85,824,000 us-gaap_FiniteLivedIntangibleAssetsGross / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = trmk_CoreDepositIntangiblesMember |
Accumulated Amortization | 54,464,000 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = trmk_CoreDepositIntangiblesMember | 46,437,000 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = trmk_CoreDepositIntangiblesMember |
Net Carrying Amount | 31,360,000 us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = trmk_CoreDepositIntangiblesMember | 39,387,000 us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = trmk_CoreDepositIntangiblesMember |
Remaining Weighted-Average Amortization Period in Years | 7 years 6 months |  |
Insurance Intangibles [Member] |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |
Gross Carrying Amount | 11,693,000 us-gaap_FiniteLivedIntangibleAssetsGross / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = trmk_InsuranceIntangiblesMember | 11,693,000 us-gaap_FiniteLivedIntangibleAssetsGross / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = trmk_InsuranceIntangiblesMember |
Accumulated Amortization | 10,566,000 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = trmk_InsuranceIntangiblesMember | 9,967,000 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = trmk_InsuranceIntangiblesMember |
Net Carrying Amount | 1,127,000 us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = trmk_InsuranceIntangiblesMember | 1,726,000 us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = trmk_InsuranceIntangiblesMember |
Remaining Weighted-Average Amortization Period in Years | 4 years 10 months 24 days |  |
Banking Charters [Member] |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |
Gross Carrying Amount | 1,325,000 us-gaap_FiniteLivedIntangibleAssetsGross / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = trmk_BankingChartersMember | 1,325,000 us-gaap_FiniteLivedIntangibleAssetsGross / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = trmk_BankingChartersMember |
Accumulated Amortization | 745,000 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = trmk_BankingChartersMember | 678,000 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = trmk_BankingChartersMember |
Net Carrying Amount | 580,000 us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = trmk_BankingChartersMember | 647,000 us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = trmk_BankingChartersMember |
Remaining Weighted-Average Amortization Period in Years | 8 years 8 months 12 days |  |
Borrower Relationship Intangible [Member] |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |
Gross Carrying Amount | 690,000 us-gaap_FiniteLivedIntangibleAssetsGross / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = trmk_BorrowerRelationshipIntangibleMember | 690,000 us-gaap_FiniteLivedIntangibleAssetsGross / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = trmk_BorrowerRelationshipIntangibleMember |
Accumulated Amortization | 523,000 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = trmk_BorrowerRelationshipIntangibleMember | 460,000 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = trmk_BorrowerRelationshipIntangibleMember |
Net Carrying Amount | 167,000 us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = trmk_BorrowerRelationshipIntangibleMember | 230,000 us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = trmk_BorrowerRelationshipIntangibleMember |
Remaining Weighted-Average Amortization Period in Years | 2 years 8 months 12 days |  |
General Banking [Member] |  |  |
Goodwill [Roll Forward] |  |  |
Goodwill, beginning of period | 328,483,000 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = trmk_GeneralBankingMember | 246,736,000 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = trmk_GeneralBankingMember |
Goodwill from acquisitions |  | 81,747,000 us-gaap_GoodwillAcquiredDuringPeriod / us-gaap_StatementBusinessSegmentsAxis = trmk_GeneralBankingMember |
Measurement period adjustment during 2014 | (7,351,000)us-gaap_GoodwillImpairedAdjustmentToInitialEstimateAmount / us-gaap_StatementBusinessSegmentsAxis = trmk_GeneralBankingMember |  |
Balance, end of period | 321,132,000 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = trmk_GeneralBankingMember | 328,483,000 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = trmk_GeneralBankingMember |
Insurance [Member] |  |  |
Goodwill [Roll Forward] |  |  |
Goodwill, beginning of period | 44,368,000 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = trmk_InsuranceMember | 44,368,000 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = trmk_InsuranceMember |
Goodwill from acquisitions |  | 0 us-gaap_GoodwillAcquiredDuringPeriod / us-gaap_StatementBusinessSegmentsAxis = trmk_InsuranceMember |
Measurement period adjustment during 2014 | 0 us-gaap_GoodwillImpairedAdjustmentToInitialEstimateAmount / us-gaap_StatementBusinessSegmentsAxis = trmk_InsuranceMember |  |
Balance, end of period | 44,368,000 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = trmk_InsuranceMember | 44,368,000 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = trmk_InsuranceMember |
BancTrust acquisition [Member] |  |  |
Goodwill [Roll Forward] |  |  |
Goodwill acquisition |  | 81,600,000 us-gaap_GoodwillTransfers / us-gaap_BusinessAcquisitionAxis = trmk_BanctrustAcquisitionMember |
SOUTHBank Branches [Member] |  |  |
Goodwill [Roll Forward] |  |  |
Goodwill acquisition |  | $ 150,000 us-gaap_GoodwillTransfers / us-gaap_BusinessAcquisitionAxis = trmk_SOUTHBankBranchesMember |
Number of branches |  | 2 trmk_NumberOfBranches / us-gaap_BusinessAcquisitionAxis = trmk_SOUTHBankBranchesMember |

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