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, 2018	Dec. 31, 2017		Dec. 31, 2016
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Service charges on deposit accounts		$ 43,702	$ 44,003	[1]	$ 45,253	[1]
Bank card and other fees		28,905	28,286	[1]	27,906	[1]
Mortgage banking, net		34,674	29,902	[1]	28,212	[1]
Wealth management		30,338	30,340	[1]	30,492	[1]
Insurance commissions		40,481	38,168	[1]	36,764	[1]
Other, net		6,736	13,949	[1]	5,626	[1]
Security gains (losses), net		0	15	[1]	(310)	[1]
Total Noninterest Income		184,836	184,663	[1]	173,943	[1]
General Banking Segment [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Service charges on deposit accounts		43,699	44,001	[1]	45,252	[1]
Bank card and other fees		28,823	28,229	[1]	27,893	[1]
Mortgage banking, net		34,674	29,902	[1]	28,212	[1]
Wealth management		296	210	[1]	566	[1]
Other, net		6,630	13,823	[1]	5,446	[1]
Security gains (losses), net	[1]		15		(310)
Total Noninterest Income		114,122	116,180	[1]	107,059	[1]
Wealth Management Segment [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Service charges on deposit accounts		3	2	[1]	1	[1]
Bank card and other fees		82	57	[1]	13	[1]
Wealth management		30,042	30,130	[1]	29,926	[1]
Other, net		101	96	[1]	177	[1]
Total Noninterest Income		30,228	30,285	[1]	30,117	[1]
Insurance Segment [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Insurance commissions		40,481	38,168	[1]	36,764	[1]
Other, net		5	30	[1]	3	[1]
Total Noninterest Income		40,486	38,198	[1]	36,767	[1]
Topic 606 [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Service charges on deposit accounts		43,702	44,003	[1]	45,253	[1]
Bank card and other fees		27,008	28,036	[1]	27,243	[1]
Wealth management		30,338	30,340	[1]	30,492	[1]
Insurance commissions		40,481	38,168	[1]	36,764	[1]
Other, net		6,835	6,596	[1]	7,271	[1]
Total Noninterest Income		148,364	147,143	[1]	147,023	[1]
Topic 606 [Member] | General Banking Segment [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Service charges on deposit accounts		43,699	44,001	[1]	45,252	[1]
Bank card and other fees		26,926	27,979	[1]	27,230	[1]
Wealth management		296	210	[1]	566	[1]
Other, net		6,826	6,565	[1]	7,185	[1]
Total Noninterest Income		77,747	78,755	[1]	80,233	[1]
Topic 606 [Member] | Wealth Management Segment [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Service charges on deposit accounts		3	2	[1]	1	[1]
Bank card and other fees		82	57	[1]	13	[1]
Wealth management		30,042	30,130	[1]	29,926	[1]
Other, net		4	1	[1]	83	[1]
Total Noninterest Income		30,131	30,190	[1]	30,023	[1]
Topic 606 [Member] | Insurance Segment [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Insurance commissions		40,481	38,168	[1]	36,764	[1]
Other, net		5	30	[1]	3	[1]
Total Noninterest Income		40,486	38,198	[1]	36,767	[1]
Not Topic 606 [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Bank card and other fees	[2]	1,897	250	[1]	663	[1]
Mortgage banking, net	[2]	34,674	29,902	[1]	28,212	[1]
Other, net	[2]	(99)	7,353	[1]	(1,645)	[1]
Security gains (losses), net	[1],[2]		15		(310)
Total Noninterest Income	[2]	36,472	37,520	[1]	26,920	[1]
Not Topic 606 [Member] | General Banking Segment [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Bank card and other fees	[2]	1,897	250	[1]	663	[1]
Mortgage banking, net	[2]	34,674	29,902	[1]	28,212	[1]
Other, net	[2]	(196)	7,258	[1]	(1,739)	[1]
Security gains (losses), net	[1],[2]		15		(310)
Total Noninterest Income	[2]	36,375	37,425	[1]	26,826	[1]
Not Topic 606 [Member] | Wealth Management Segment [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Other, net	[2]	97	95	[1]	94	[1]
Total Noninterest Income	[2]	$ 97	$ 95	[1]	$ 94	[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 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