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, 2022	Dec. 31, 2021	Dec. 31, 2020
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	$ 8,647	$ 9,547
Service cost	115	252	$ 254
Interest cost	192	173	241
Actuarial (gain) loss	(1,882)	(198)
Benefits paid	(165)	(1,127)
Benefit obligation, end of year	6,907	8,647	9,547
Change in plan assets [ Roll Forward]
Fair value of plan assets, beginning of year	2,900	2,873
Actual return on plan assets	(285)	291
Employer contributions	457	863
Benefit payments	(165)	(1,127)
Fair value of plan assets, end of year	2,907	2,900	2,873
Funded status at end of year - net liability	(4,000)	(5,747)
Amounts recognized in accumulated other comprehensive income (loss) [Abstract]
Net (gain) loss	(271)	1,428
Actuarial (gain) loss included in benefit obligation:
Change in discount rate	(2,174)	(491)
Change in mortality table	(0)	15
Other	292	278
Actuarial (gain) loss	(1,882)	(198)
Supplemental Retirement Plan [Member]
Change in benefit obligation [Roll Forward]
Benefit obligation, beginning of year	55,035	59,646
Service cost	71	75	77
Interest cost	1,278	1,125	1,576
Actuarial (gain) loss	(9,195)	(2,357)
Benefits paid	(3,988)	(3,454)
Benefit obligation, end of year	43,201	55,035	$ 59,646
Change in plan assets [ Roll Forward]
Employer contributions	3,988	3,454
Benefit payments	(3,988)	(3,454)
Funded status at end of year - net liability	(43,201)	(55,035)
Amounts recognized in accumulated other comprehensive income (loss) [Abstract]
Net (gain) loss	7,756	17,937
Prior service cost	237	348
Amounts recognized	7,993	18,285
Actuarial (gain) loss included in benefit obligation:
Change in discount rate	9,803	(2,431)
Change in mortality table	(0)	134
Other	(608)	(60)
Actuarial (gain) loss	$ (9,195)	$ (2,357)