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Defined Benefit and Other Postretirement Benefits - Additional Information (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2026 | Dec. 31, 2025 | Dec. 31, 2024 | Dec. 31, 2023
Pension Plan [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Trustmark's minimum required contribution to the Trustmark Corporation Pension Plan for Certain Employees of Acquired Financial Institutions |  | $ 98 |  |
Trustmark's contribution to the Trustmark Corporation Pension Plan for Certain Employees of Acquired Financial Institutions |  | 109 |  |
Estimated future benefit payments [Abstract] |  |  |  |
Accumulated other comprehensive income (loss) expected to be recognized during next fiscal year as components of net periodic benefit cost |  | 317 |  |
Pension Plan [Member] | Forecast |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Trustmark's minimum required contribution to the Trustmark Corporation Pension Plan for Certain Employees of Acquired Financial Institutions | $ 91 |  |  |
Supplemental Retirement Plan [Member] |  |  |  |
Estimated future benefit payments [Abstract] |  |  |  |
Accumulated other comprehensive income (loss) expected to be recognized during next fiscal year as components of net periodic benefit cost |  | 14 |  |
Defined Contribution Plan [Member] |  |  |  |
Other Benefit Plans - Defined Contribution Plan [Abstract] |  |  |  |
Trustmarks contribution to defined contribution plan |  | $ 10,400 | $ 10,700 | $ 10,800
Contributions up to a maximum of eligible compensation |  | 6.00% |  |
Automatically enrolled Contributions of eligible compensation |  | 3.00% |  |
Trustmark contributions to the plan |  | 100.00% |  |
Period when associates may become eligible to make elective deferral contributions after employment |  | 60 days |  |

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