Revenue from Contracts with Customers - Summary of Noninterest Income Disaggregated by Reportable Operating Segment and Revenue Stream (Details) - USD ($) $ in Thousands		3 Months Ended			6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017		Jun. 30, 2018	Jun. 30, 2017
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Service charges on deposit accounts		$ 10,647	$ 10,755	[1]	$ 21,504	$ 21,587	[1]
Bank card and other fees		7,070	7,370	[1]	13,696	13,870	[1]
Mortgage banking, net		9,046	9,008	[1]	20,311	19,193	[1]
Insurance commissions		10,735	9,745	[1]	20,154	18,957	[1]
Wealth management		7,478	7,674	[1]	15,045	15,087	[1]
Other, net		2,415	5,637	[1]	3,474	7,528	[1]
Security gains (losses), net			1	[1]	0	1	[1]
Total Noninterest Income		47,391	50,190	[1]	94,184	96,223	[1]
Topic 606 [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Service charges on deposit accounts		10,647	10,755	[1]	21,504	21,587	[1]
Bank card and other fees		6,854	7,209	[1]	13,406	13,685	[1]
Insurance commissions		10,735	9,745	[1]	20,154	18,957	[1]
Wealth management		7,478	7,674	[1]	15,045	15,087	[1]
Other, net		1,543	1,163	[1]	2,984	3,507	[1]
Total Noninterest Income		37,257	36,546	[1]	73,093	72,823	[1]
Not Topic 606 [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Bank card and other fees	[2]	216	161	[1]	290	185	[1]
Mortgage banking, net	[2]	9,046	9,008	[1]	20,311	19,193	[1]
Other, net	[2]	872	4,474	[1]	490	4,021	[1]
Security gains (losses), net	[1],[2]		1			1
Total Noninterest Income	[2]	10,134	13,644	[1]	21,091	23,400	[1]
General Banking Division [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Service charges on deposit accounts		10,646	10,755	[1]	21,503	21,587	[1]
Bank card and other fees		7,048	7,362	[1]	13,652	13,858	[1]
Mortgage banking, net		9,046	9,008	[1]	20,311	19,193	[1]
Wealth management		93	83	[1]	140	146	[1]
Other, net		2,388	5,611	[1]	3,424	7,475	[1]
Security gains (losses), net	[1]		1			1
Total Noninterest Income		29,221	32,820	[1]	59,030	62,260	[1]
General Banking Division [Member] | Topic 606 [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Service charges on deposit accounts		10,646	10,755	[1]	21,503	21,587	[1]
Bank card and other fees		6,832	7,201	[1]	13,362	13,673	[1]
Wealth management		93	83	[1]	140	146	[1]
Other, net		1,541	1,162	[1]	2,981	3,502	[1]
Total Noninterest Income		19,112	19,201	[1]	37,986	38,908	[1]
General Banking Division [Member] | Not Topic 606 [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Bank card and other fees	[2]	216	161	[1]	290	185	[1]
Mortgage banking, net	[2]	9,046	9,008	[1]	20,311	19,193	[1]
Other, net	[2]	847	4,449	[1]	443	3,973	[1]
Security gains (losses), net	[1],[2]		1			1
Total Noninterest Income	[2]	10,109	13,619	[1]	21,044	23,352	[1]
Wealth Management Division [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Service charges on deposit accounts		1			1
Bank card and other fees		22	8	[1]	44	12	[1]
Wealth management		7,385	7,591	[1]	14,905	14,941	[1]
Other, net		26	25	[1]	49	48	[1]
Total Noninterest Income		7,434	7,624	[1]	14,999	15,001	[1]
Wealth Management Division [Member] | Topic 606 [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Service charges on deposit accounts		1			1
Bank card and other fees		22	8	[1]	44	12	[1]
Wealth management		7,385	7,591	[1]	14,905	14,941	[1]
Other, net		1			2
Total Noninterest Income		7,409	7,599	[1]	14,952	14,953	[1]
Wealth Management Division [Member] | Not Topic 606 [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Other, net	[2]	25	25	[1]	47	48	[1]
Total Noninterest Income	[2]	25	25	[1]	47	48	[1]
Insurance Division [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Insurance commissions		10,735	9,745	[1]	20,154	18,957	[1]
Other, net		1	1	[1]	1	5	[1]
Total Noninterest Income		10,736	9,746	[1]	20,155	18,962	[1]
Insurance Division [Member] | Topic 606 [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Insurance commissions		10,735	9,745	[1]	20,154	18,957	[1]
Other, net		1	1	[1]	1	5	[1]
Total Noninterest Income		$ 10,736	$ 9,746	[1]	$ 20,155	$ 18,962	[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.