Defined Benefit and Other Postretirement Benefits (Tables)

12 Months Ended

Dec. 31, 2023

Trustmark Capital Accumulation Plan [Member]

Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]

Plan Benefit Obligation, Plan Assets and Funded Status of the Plan

The following tables present information regarding the benefit obligation, plan assets, funded status, amounts recognized in accumulated other comprehensive loss, net periodic benefit cost and other statistical disclosures for the Continuing Plan for the periods presented ($ in thousands):

	December 31,
	2023			2022
Change in benefit obligation:
Benefit obligation, beginning of year	$	6,907		$	8,647
Service cost		52			115
Interest cost		292			192
Actuarial (gain) loss		164			(1,882	)
Benefits paid		(1,492	)		(165	)
Benefit obligation, end of year	$	5,923		$	6,907
Change in plan assets:
Fair value of plan assets, beginning of year	$	2,907		$	2,900
Actual return on plan assets		237			(285	)
Employer contributions		751			457
Benefit payments		(1,492	)		(165	)
Fair value of plan assets, end of year	$	2,403		$	2,907
Funded status at end of year - net liability	$	(3,520	)	$	(4,000	)
Amounts recognized in accumulated other comprehensive loss:
Net (gain) loss - amount recognized	$	(262	)	$	(271	)
Actuarial (gain) loss included in benefit obligation:
Change in discount rate	$	124		$	(2,174	)
Change in mortality table		(38	)		—
Other		78			292
Actuarial (gain) loss	$	164		$	(1,882	)

Net Periodic Benefit Cost

	Years Ended December 31,
	2023			2022			2021
Net periodic benefit cost:
Service cost	$	52		$	115		$	252
Interest cost		292			192			173
Expected return on plan assets		(107	)		(121	)		(130	)
Recognized net loss due to lump sum settlements		25			—			183
Recognized net actuarial loss		—			224			594
Net periodic benefit cost	$	262		$	410		$	1,072
Other changes in plan assets and benefit obligation recognized in other    comprehensive income (loss), before taxes:
Net loss - Total recognized in other comprehensive income (loss)	$	9		$	(1,699	)	$	(1,136	)
Total recognized in net periodic benefit cost and other comprehensive    income (loss)	$	271		$	(1,289	)	$	(64	)
Weighted-average assumptions as of end of year:
Discount rate for benefit obligation		4.67	%		4.88	%		2.41	%
Discount rate for net periodic benefit cost		4.88	%		2.41	%		1.95	%
Expected long-term return on plan assets		5.00	%		5.00	%		5.00	%

Weighted-Average Asset Allocation

The weighted-average asset allocations by asset category are presented below for the Continuing Plan at December 31, 2023 and 2022.

	December 31,
	2023			2022
Money market fund		27.0	%		7.0	%
Exchange traded funds:
Equity securities		36.0	%		47.0	%
Fixed income		28.0	%		39.0	%
International		9.0	%		7.0	%
Total		100.0	%		100.0	%

Plan Assets Measured at Fair Value

The following tables set forth by level, within the fair value hierarchy, the Continuing Plan’s assets measured at fair value at December 31, 2023 and 2022 ($ in thousands):

	December 31, 2023
	Total		Level 1		Level 2		Level 3
Money market fund	$	643	$	643	$	—	$	—
Exchange traded funds:
Equity securities		861		861		—		—
Fixed income		690		690		—		—
International		209		209		—		—
Total assets at fair value	$	2,403	$	2,403	$	—	$	—

	December 31, 2022
	Total		Level 1		Level 2		Level 3
Money market fund	$	203	$	203	$	—	$	—
Exchange traded funds:
Equity securities		1,379		1,379		—		—
Fixed income		1,135		1,135		—		—
International		190		190		—		—
Total assets at fair value	$	2,907	$	2,907	$	—	$	—

Estimated Future Benefit Payments and Other Disclosures

The following table presents the expected benefit payments, which reflect expected future service, for the Continuing Plan ($ in thousands):

Year	Amount
2024	$	1,312
2025		682
2026		701
2027		724
2028		428
2029 - 2033		1,396

Supplemental Retirement Plan [Member]

Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]

Plan Benefit Obligation, Plan Assets and Funded Status of the Plan

The following tables present information regarding the benefit obligation, plan assets, funded status, amounts recognized in accumulated other comprehensive loss, net periodic benefit cost and other statistical disclosures for Trustmark’s nonqualified supplemental retirement plans for the periods presented ($ in thousands):

	December 31,
	2023			2022
Change in benefit obligation:
Benefit obligation, beginning of year	$	43,201		$	55,035
Service cost		69			71
Interest cost		2,013			1,278
Actuarial (gain) loss		763			(9,195	)
Benefits paid		(4,427	)		(3,988	)
Benefit obligation, end of year	$	41,619		$	43,201
Change in plan assets:
Fair value of plan assets, beginning of year	$	—		$	—
Employer contributions		4,427			3,988
Benefit payments		(4,427	)		(3,988	)
Fair value of plan assets, end of year	$	—		$	—
Funded status at end of year - net liability	$	(41,619	)	$	(43,201	)
Amounts recognized in accumulated other comprehensive loss:
Net loss	$	8,235		$	7,756
Prior service cost		126			237
Amounts recognized	$	8,361		$	7,993
Actuarial (gain) loss included in benefit obligation:
Change in discount rate	$	649		$	(9,803	)
Change in mortality table		(308	)		—
Other		422			608
Actuarial (gain) loss	$	763		$	(9,195	)

Net Periodic Benefit Cost

	Years Ended December 31,
	2023			2022			2021
Net periodic benefit cost:
Service cost	$	69		$	71		$	75
Interest cost		2,013			1,278			1,125
Amortization of prior service cost		111			111			111
Recognized net actuarial loss		284			986			1,192
Net periodic benefit cost	$	2,477		$	2,446		$	2,503
Other changes in plan assets and benefit obligation recognized in other    comprehensive income (loss), before taxes:
Net (gain) loss	$	479		$	(10,181	)	$	(3,549	)
Amortization of prior service cost		(111	)		(111	)		(111	)
Total recognized in other comprehensive income (loss)	$	368		$	(10,292	)	$	(3,660	)
Total recognized in net periodic benefit cost and other comprehensive    income (loss)	$	2,845		$	(7,846	)	$	(1,157	)
Weighted-average assumptions as of end of year:
Discount rate for benefit obligation		4.67	%		4.88	%		2.41	%
Discount rate for net periodic benefit cost		4.88	%		2.41	%		1.95	%

Estimated Future Benefit Payments and Other Disclosures

The following table presents the expected benefits payments for Trustmark’s supplemental retirement plans ($ in thousands):

Year	Amount
2024	$	3,997
2025		3,871
2026		3,825
2027		3,641
2028		3,520
2029 - 2033		16,051