Defined Benefit and Other Postretirement Benefits - Plan Benefit Obligation, Plan Assets and Funded Status of the Plan (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Trustmark Capital Accumulation Plan [Member] | Trustmark Corporation Pension Plan for Certain Employees of Acquired Financial Institutions [Member]
Change in benefit obligation [Roll Forward]
Benefit obligation, beginning of year	$ 9,547	$ 9,060
Service cost	252	254	$ 211
Interest cost	173	241	361
Actuarial (gain) loss	(198)	876
Benefits paid	(1,127)	(884)
Benefit obligation, end of year	8,647	9,547	9,060
Change in plan assets [ Roll Forward]
Fair value of plan assets, beginning of year	2,873	3,443
Actual return on plan assets	291	(87)
Employer contributions	863	401
Benefit payments	(1,127)	(884)
Fair value of plan assets, end of year	2,900	2,873	3,443
Funded status at end of year - net liability	(5,747)	(6,674)
Amounts recognized in accumulated other comprehensive income (loss) [Abstract]
Net loss	1,428	2,564
Actuarial (gain) loss included in benefit obligation:
Change in discount rate	(491)	1,009
Change in mortality table	15	(47)
Other	278	(86)
Actuarial (gain) loss	(198)	876
Supplemental Retirement Plan [Member]
Change in benefit obligation [Roll Forward]
Benefit obligation, beginning of year	59,646	57,482
Service cost	75	77	109
Interest cost	1,125	1,576	2,044
Actuarial (gain) loss	(2,357)	4,168
Benefits paid	(3,454)	(3,657)
Benefit obligation, end of year	55,035	59,646	$ 57,482
Change in plan assets [ Roll Forward]
Employer contributions	3,454	3,657
Benefit payments	(3,454)	(3,657)
Funded status at end of year - net liability	(55,035)	(59,646)
Amounts recognized in accumulated other comprehensive income (loss) [Abstract]
Net loss	17,937	21,486
Prior service cost	348	459
Amounts recognized	18,285	21,945
Actuarial (gain) loss included in benefit obligation:
Change in discount rate	(2,431)	4,997
Change in mortality table	134	(380)
Other	(60)	(449)
Actuarial (gain) loss	$ (2,357)	$ 4,168