Revenue from Contracts with Customers - Summary of Noninterest Income Disaggregated by Reportable Operating Segment and Revenue Stream (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017
Revenue From Contract With Customer [Line Items]
Service charges on deposit accounts		$ 42,603	$ 43,702	[1]	$ 44,003	[1],[2]
Bank card and other fees		31,736	28,905	[1]	28,286	[1],[2]
Mortgage banking, net		29,822	34,674	[1]	29,902	[1],[2]
Insurance commissions		42,396	40,481	[1]	38,168	[1],[2]
Wealth management		30,679	30,338	[1]	30,340	[1],[2]
Other, net		9,809	6,736	[1]	13,949	[1],[2]
Security gains (losses), net		0	0		15	[1],[2]
Total Noninterest Income		187,045	184,836	[1]	184,663	[1],[2]
Topic 606 [Member]
Revenue From Contract With Customer [Line Items]
Service charges on deposit accounts		42,603	43,702	[1]	44,003	[1],[2]
Bank card and other fees		28,030	27,008	[1]	28,036	[1],[2]
Insurance commissions		42,396	40,481	[1]	38,168	[1],[2]
Wealth management		30,679	30,338	[1]	30,340	[1],[2]
Other, net		9,866	6,836	[1]	6,597	[1],[2]
Total Noninterest Income		153,574	148,365	[1]	147,144	[1],[2]
Not Topic 606 [Member]
Revenue From Contract With Customer [Line Items]
Bank card and other fees	[3]	3,706	1,897	[1]	250	[1],[2]
Mortgage banking, net	[3]	29,822	34,674	[1]	29,902	[1],[2]
Other, net	[3]	(57)	(100)	[1]	7,352	[1],[2]
Security gains (losses), net	[1],[2],[3]				15
Total Noninterest Income	[3]	33,471	36,471	[1]	37,519	[1],[2]
General Banking Segment [Member]
Revenue From Contract With Customer [Line Items]
Service charges on deposit accounts		42,509	43,614	[1]	43,928	[1],[2]
Bank card and other fees		31,678	28,801	[1]	28,208	[1],[2]
Mortgage banking, net		29,822	34,674	[1]	29,902	[1],[2]
Wealth management		379	296	[1]	210	[1],[2]
Other, net		9,367	6,545	[1]	13,781	[1],[2]
Security gains (losses), net	[1],[2]				15
Total Noninterest Income		113,755	113,930	[1]	116,044	[1],[2]
General Banking Segment [Member] | Topic 606 [Member]
Revenue From Contract With Customer [Line Items]
Service charges on deposit accounts		42,509	43,614	[1]	43,928	[1],[2]
Bank card and other fees		27,972	26,904	[1]	27,958	[1],[2]
Wealth management		379	296	[1]	210	[1],[2]
Other, net		9,527	6,762	[1]	6,547	[1],[2]
Total Noninterest Income		80,387	77,576	[1]	78,643	[1],[2]
General Banking Segment [Member] | Not Topic 606 [Member]
Revenue From Contract With Customer [Line Items]
Bank card and other fees	[3]	3,706	1,897	[1]	250	[1],[2]
Mortgage banking, net	[3]	29,822	34,674	[1]	29,902	[1],[2]
Other, net	[3]	(160)	(217)	[1]	7,234	[1],[2]
Security gains (losses), net	[1],[2],[3]				15
Total Noninterest Income	[3]	33,368	36,354	[1]	37,401	[1],[2]
Wealth Management Segment [Member]
Revenue From Contract With Customer [Line Items]
Service charges on deposit accounts		94	88	[1]	75	[1],[2]
Bank card and other fees		58	104	[1]	78	[1],[2]
Wealth management		30,300	30,042	[1]	30,130	[1],[2]
Other, net		409	186	[1]	138	[1],[2]
Total Noninterest Income		30,861	30,420	[1]	30,421	[1],[2]
Wealth Management Segment [Member] | Topic 606 [Member]
Revenue From Contract With Customer [Line Items]
Service charges on deposit accounts		94	88	[1]	75	[1],[2]
Bank card and other fees		58	104	[1]	78	[1],[2]
Wealth management		30,300	30,042	[1]	30,130	[1],[2]
Other, net		306	69	[1]	20	[1],[2]
Total Noninterest Income		30,758	30,303	[1]	30,303	[1],[2]
Wealth Management Segment [Member] | Not Topic 606 [Member]
Revenue From Contract With Customer [Line Items]
Other, net	[3]	103	117	[1]	118	[1],[2]
Total Noninterest Income	[3]	103	117	[1]	118	[1],[2]
Insurance Segment [Member]
Revenue From Contract With Customer [Line Items]
Insurance commissions		42,396	40,481	[1]	38,168	[1],[2]
Other, net		33	5	[1]	30	[1],[2]
Total Noninterest Income		42,429	40,486	[1]	38,198	[1],[2]
Insurance Segment [Member] | Topic 606 [Member]
Revenue From Contract With Customer [Line Items]
Insurance commissions		42,396	40,481	[1]	38,168	[1],[2]
Other, net		33	5	[1]	30	[1],[2]
Total Noninterest Income		$ 42,429	$ 40,486	[1]	$ 38,198	[1],[2]

[1] During the first quarter of 2019, Trustmark revised the composition of its operating segments by moving the Private Banking Group from the General Banking Segment to the Wealth Management Segment as a result of a change in supervision of this group for segment reporting purposes.  The prior period amounts presented include reclassifications to conform to the current period presentation.

[2] 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.

[3] Noninterest income not in scope for FASB ASC Topic 606 includes customer derivatives revenue and miscellaneous credit card 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 securities gains (losses), net.