Defined Benefit and Other Postretirement Benefits - Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands |
3 Months Ended | |
|---|---|---|
Mar. 31, 2026 |
Mar. 31, 2025 |
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| Trustmark Capital Accumulation Plan [Member] | Trustmark Corporation Pension Plan for Certain Employees of Acquired Financial Institutions [Member] | ||
| Net periodic benefit cost [Abstract] | ||
| Service cost | $ 7 | $ 9 |
| Interest cost | 50 | 69 |
| Expected return on plan assets | (19) | (32) |
| Recognized net (gain) loss due to lump sum settlements | 0 | (50) |
| Recognized net actuarial (gain) loss | (3) | (2) |
| Net periodic benefit cost | 35 | (6) |
| Supplemental Retirement Plan [Member] | ||
| Net periodic benefit cost [Abstract] | ||
| Service cost | 2 | 4 |
| Interest cost | 451 | 495 |
| Amortization of prior service cost | 0 | 4 |
| Recognized net actuarial (gain) loss | 88 | 73 |
| Net periodic benefit cost | $ 541 | $ 576 |
| X | ||||||||||
- Definition Amount of gain (loss), recognized immediately as component of net periodic benefit (cost) credit, for change in value of benefit obligation or plan assets from experience different from that assumed, change in actuarial assumption, or consequence of temporarily deviating from substantive plan. Includes, but is not limited to, amount in excess of 10 percent of greater of fair value of plan assets or benefit obligation. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount of prior service cost (credit) recognized in net periodic benefit cost (credit) of defined benefit plan. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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- Definition Amount of expected return (loss) recognized in net periodic benefit (cost) credit, calculated based on expected long-term rate of return and market-related value of plan assets of defined benefit plan. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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- Definition Amount of cost recognized for passage of time related to defined benefit plan. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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- Definition Amount of net periodic benefit cost (credit) for defined benefit plan. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- References No definition available.
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- Definition Amount of gain (loss) recognized in net periodic benefit (cost) credit from irrevocable action relieving primary responsibility for benefit obligation and eliminating risk related to obligation and assets used to effect settlement. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount of cost for actuarial present value of benefits attributed to service rendered by employee for defined benefit plan. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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