Defined Benefit and Other Postretirement Benefits (Tables)

12 Months Ended

Dec. 31, 2017

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 Trustmark’s tax-qualified defined benefit pension plans (the Continuing Plan and the Plan) for the periods presented ($ in thousands):

	December 31,
	2017			2016
Change in benefit obligation:
Benefit obligation, beginning of year	$	75,900		$	91,403
Service cost		253			428
Interest cost		1,461			3,355
Actuarial loss (gain)		391			(893	)
Benefits paid for the Plan		(68,583	)		(18,393	)
Settlement loss		680			—
Benefit obligation, end of year	$	10,102		$	75,900
Change in plan assets:
Fair value of plan assets, beginning of year	$	54,734		$	74,137
Actual return on plan assets		481			(1,079	)
Employer contributions		17,964			69
Benefit payments for the Plan		(68,583	)		(18,393	)
Fair value of plan assets, end of year	$	4,596		$	54,734
Funded status at end of year - net liability	$	(5,506	)	$	(21,166	)
Amounts recognized in accumulated other comprehensive loss:
Net loss - amount recognized	$	3,187		$	21,355

Net Periodic Benefit Cost

	Years Ended December 31,
	2017			2016			2015
Net periodic benefit cost:
Service cost	$	253		$	428		$	513
Interest cost		1,461			3,355			3,461
Expected return on plan assets		(317	)		(2,897	)		(5,187	)
Recognized net loss due to defined benefit plan termination		17,662			—			—
Recognized net loss due to lump sum settlements		—			3,906			2,221
Recognized net actuarial loss		1,414			2,749			3,878
Net periodic benefit cost	$	20,473		$	7,541		$	4,886
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)	$	(18,168	)	$	(3,572	)	$	(3,173	)
Total recognized in net periodic benefit cost and other comprehensive    income (loss)	$	2,305		$	3,969		$	1,713
Weighted-average assumptions as of end of year:
Discount rate for benefit obligation		3.32	%		3.71	%		3.86	%
Discount rate for net periodic benefit cost		3.71	%		3.86	%		3.57	%
Expected long-term return on plan assets		5.00	%		4.25	%		7.00	%

Weighted-Average Asset Allocation

The weighted-average asset allocations by asset category are presented below for the Continuing Plan at December 31, 2017 and 2016, and for the Plan at December 31, 2016.  No assets remained in the Plan at December 31, 2017.  

	December 31,
	2017			2016
Money market fund		6.0	%		13.0	%
U.S. Treasuries		—			87.0	%
Exchange traded funds:
Equity securities		48.0	%		—
Fixed income		32.0	%		—
International		14.0	%		—
Total		100.0	%		100.0	%

Plan Assets Measured at Fair Value

The following table sets forth by level, within the fair value hierarchy, the Continuing Plan’s assets measured at fair value at December 31, 2017 and 2016 and the Plan’s assets at December 31, 2016 ($ in thousands):

	December 31, 2017
	Total		Level 1		Level 2		Level 3
Money market fund	$	269	$	269	$	—	$	—
Exchange traded funds:
Equity securities		2,199		2,199		—		—
Fixed income		1,462		1,462		—		—
International		666		666		—		—
Total assets at fair value	$	4,596	$	4,596	$	—	$	—

	December 31, 2016
	Total		Level 1		Level 2		Level 3
Money market fund	$	6,859	$	6,859	$	—	$	—
U.S. Treasuries		47,875		47,875		—		—
Total assets at fair value	$	54,734	$	54,734	$	—	$	—

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
2018	$	196
2019		282
2020		333
2021		394
2022		453
2023 - 2027		2,961

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 ($ in thousands):

	December 31,
	2017			2016
Change in benefit obligation:
Benefit obligation, beginning of year	$	58,495		$	57,766
Service cost		141			295
Interest cost		2,103			2,223
Actuarial loss		642			1,537
Benefits paid		(3,451	)		(3,326	)
Benefit obligation, end of year	$	57,930		$	58,495
Change in plan assets:
Fair value of plan assets, beginning of year	$	—		$	—
Employer contributions		3,451			3,326
Benefit payments		(3,451	)		(3,326	)
Fair value of plan assets, end of year	$	—		$	—
Funded status at end of year - net liability	$	(57,930	)	$	(58,495	)
Amounts recognized in accumulated other comprehensive loss:
Net loss	$	17,514		$	17,739
Prior service cost		1,109			1,359
Amounts recognized	$	18,623		$	19,098

Net Periodic Benefit Cost

	Years Ended December 31,
	2017			2016			2015
Net periodic benefit cost:
Service cost	$	141		$	295		$	431
Interest cost		2,103			2,223			2,082
Amortization of prior service cost		250			250			250
Recognized net actuarial loss		866			864			992
Net periodic benefit cost	$	3,360		$	3,632		$	3,755
Other changes in plan assets and benefit obligation recognized in other    comprehensive income (loss), before taxes:
Net (gain) loss	$	(224	)	$	(810	)	$	(2,694	)
Amortization of prior service cost		(250	)		(250	)		(250	)
Total recognized in other comprehensive income (loss)	$	(474	)	$	(1,060	)	$	(2,944	)
Total recognized in net periodic benefit cost and other comprehensive    income (loss)	$	2,886		$	2,572		$	811
Weighted-average assumptions as of end of year:
Discount rate for benefit obligation		3.32	%		3.71	%		3.86	%
Discount rate for net periodic benefit cost		3.71	%		3.86	%		3.57	%

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
2018	$	3,475
2019		3,591
2020		4,047
2021		4,105
2022		4,262
2023 - 2027		19,230