Segment Information - Schedule of Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017		Sep. 30, 2018	Sep. 30, 2017		Dec. 31, 2017
Segment Reporting Information [Line Items]
Net interest income	$ 106,983	$ 103,912		$ 314,240	$ 303,506
Provision for loan losses, net	8,206	2,019		15,043	3,533
Noninterest income	47,093	44,480	[1]	141,277	140,703	[1]
Noninterest expense	105,223	103,086		311,488	327,218
Income Before Income Taxes	40,647	43,287		128,986	113,458
Income taxes	4,394	8,708		16,090	23,596
Net Income	36,253	34,579		112,896	89,862
Selected Financial Information
Total assets	13,439,812	13,884,655		13,439,812	13,884,655		$ 13,797,953
Depreciation and amortization	9,978	10,052		29,512	28,781
General Banking [Member]
Segment Reporting Information [Line Items]
Net interest income	106,784	103,408		313,299	302,613
Provision for loan losses, net	8,206	2,019		15,043	3,533
Noninterest income	28,557	26,570	[1]	87,587	88,830	[1]
Noninterest expense	89,889	88,814		267,462	284,420
Income Before Income Taxes	37,246	39,145		118,381	103,490
Income taxes	3,536	7,130		13,430	19,772
Net Income	33,710	32,015		104,951	83,718
Selected Financial Information
Total assets	13,364,636	13,811,335		13,364,636	13,811,335
Depreciation and amortization	9,759	9,863		28,959	28,196
Wealth Management [Member]
Segment Reporting Information [Line Items]
Net interest income	134	434		771	718
Noninterest income	7,769	7,512	[1]	22,768	22,513	[1]
Noninterest expense	7,194	6,791		19,996	20,361
Income Before Income Taxes	709	1,155		3,543	2,870
Income taxes	177	441		886	1,098
Net Income	532	714		2,657	1,772
Selected Financial Information
Total assets	9,411	6,635		9,411	6,635
Depreciation and amortization	64	30		116	104
Insurance [Member]
Segment Reporting Information [Line Items]
Net interest income	65	70		170	175
Noninterest income	10,767	10,398	[1]	30,922	29,360	[1]
Noninterest expense	8,140	7,481		24,030	22,437
Income Before Income Taxes	2,692	2,987		7,062	7,098
Income taxes	681	1,137		1,774	2,726
Net Income	2,011	1,850		5,288	4,372
Selected Financial Information
Total assets	65,765	66,685		65,765	66,685
Depreciation and amortization	$ 155	$ 159		$ 437	$ 481

[1] Trustmark elected the modified retrospective approach of adoption; therefore, prior period balances are presented under legacy GAAP and may not be comparable to current year presentation.