Revenue from Contracts with Customers - Summary of Noninterest Income Disaggregated by Reportable Operating Segment and Revenue Stream (Details) - USD ($) $ in Thousands		3 Months Ended			9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017		Sep. 30, 2018	Sep. 30, 2017
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Service charges on deposit accounts		$ 11,075	$ 11,223	[1]	$ 32,579	$ 32,810	[1]
Bank card and other fees		7,459	7,150	[1]	21,155	21,020	[1]
Mortgage banking, net		8,647	4,425	[1]	28,958	23,618	[1]
Insurance commissions		10,765	10,398	[1]	30,919	29,355	[1]
Wealth management		7,789	7,530	[1]	22,834	22,617	[1]
Other, net		1,358	3,740	[1]	4,832	11,268	[1]
Security gains (losses), net			14	[1]	0	15	[1]
Total Noninterest Income		47,093	44,480	[1]	141,277	140,703	[1]
Topic 606 [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Service charges on deposit accounts		11,075	11,223	[1]	32,579	32,810	[1]
Bank card and other fees		6,522	7,127	[1]	19,928	20,812	[1]
Insurance commissions		10,765	10,398	[1]	30,919	29,355	[1]
Wealth management		7,789	7,530	[1]	22,834	22,617	[1]
Other, net		1,688	1,495	[1]	4,672	5,002	[1]
Total Noninterest Income		37,839	37,773	[1]	110,932	110,596	[1]
Not Topic 606 [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Bank card and other fees	[2]	937	23	[1]	1,227	208	[1]
Mortgage banking, net	[2]	8,647	4,425	[1]	28,958	23,618	[1]
Other, net	[2]	(330)	2,245	[1]	160	6,266	[1]
Security gains (losses), net	[1],[2]		14			15
Total Noninterest Income	[2]	9,254	6,707	[1]	30,345	30,107	[1]
General Banking Division [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Service charges on deposit accounts		11,074	11,222	[1]	32,577	32,809	[1]
Bank card and other fees		7,440	7,127	[1]	21,092	20,985	[1]
Mortgage banking, net		8,647	4,425	[1]	28,958	23,618	[1]
Wealth management		70	64	[1]	210	210	[1]
Other, net		1,326	3,718	[1]	4,750	11,193	[1]
Security gains (losses), net	[1]		14			15
Total Noninterest Income		28,557	26,570	[1]	87,587	88,830	[1]
General Banking Division [Member] | Topic 606 [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Service charges on deposit accounts		11,074	11,222	[1]	32,577	32,809	[1]
Bank card and other fees		6,503	7,104	[1]	19,865	20,777	[1]
Wealth management		70	64	[1]	210	210	[1]
Other, net		1,685	1,495	[1]	4,666	4,997	[1]
Total Noninterest Income		19,332	19,885	[1]	57,318	58,793	[1]
General Banking Division [Member] | Not Topic 606 [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Bank card and other fees	[2]	937	23	[1]	1,227	208	[1]
Mortgage banking, net	[2]	8,647	4,425	[1]	28,958	23,618	[1]
Other, net	[2]	(359)	2,223	[1]	84	6,196	[1]
Security gains (losses), net	[1],[2]		14			15
Total Noninterest Income	[2]	9,225	6,685	[1]	30,269	30,037	[1]
Wealth Management Division [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Service charges on deposit accounts		1	1	[1]	2	1	[1]
Bank card and other fees		19	23	[1]	63	35	[1]
Wealth management		7,719	7,466	[1]	22,624	22,407	[1]
Other, net		30	22	[1]	79	70	[1]
Total Noninterest Income		7,769	7,512	[1]	22,768	22,513	[1]
Wealth Management Division [Member] | Topic 606 [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Service charges on deposit accounts		1	1	[1]	2	1	[1]
Bank card and other fees		19	23	[1]	63	35	[1]
Wealth management		7,719	7,466	[1]	22,624	22,407	[1]
Other, net		1			3
Total Noninterest Income		7,740	7,490	[1]	22,692	22,443	[1]
Wealth Management Division [Member] | Not Topic 606 [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Other, net	[2]	29	22	[1]	76	70	[1]
Total Noninterest Income	[2]	29	22	[1]	76	70	[1]
Insurance Division [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Insurance commissions		10,765	10,398	[1]	30,919	29,355	[1]
Other, net		2			3	5	[1]
Total Noninterest Income		10,767	10,398	[1]	30,922	29,360	[1]
Insurance Division [Member] | Topic 606 [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Insurance commissions		10,765	10,398	[1]	30,919	29,355	[1]
Other, net		2			3	5	[1]
Total Noninterest Income		$ 10,767	$ 10,398	[1]	$ 30,922	$ 29,360	[1]

[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.

[2] Noninterest income not in scope for FASB ASC Topic 606 includes customer derivatives revenue and miscellaneous credit card fee income within bank card and other fees; mortgage banking, net; amortization of tax credits, accretion of the FDIC indemnification asset, cash surrender value on various life insurance policies, earnings on Trustmark’s non-qualified deferred compensation plans, other partnership investments and rental income within other, net; and security gains (losses), net.