Parent Company Only Financial Information - Parent Only Financial Statements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Assets
Other assets	$ 498,864	$ 532,442
Total Assets	13,286,460	13,797,953	$ 13,352,333
Liabilities and Shareholders' Equity:
Junior subordinated debt securities	61,856	61,856
Shareholders' equity	1,591,453	1,571,701	1,520,208	$ 1,473,057
Total Liabilities and Shareholders' Equity	13,286,460	13,797,953
Expense:
Net Income	149,584	105,630	108,411
Operating Activities
Net income	149,584	105,630	108,411
Adjustments to reconcile net income to net cash provided by operating activities:
Other	(3,016)	6,430	2,932
Net cash from operating activities	239,198	206,607	148,337
Investing Activities
Net cash from investing activities	438,787	(348,862)	(649,664)
Financing Activities
Cash dividends paid on common stock	(62,425)	(62,795)	(62,666)
Net cash from financing activities	(664,192)	150,317	551,282
Net change in cash and cash equivalents	13,793	8,062	49,955
Cash and cash equivalents at beginning of year	335,768	327,706	277,751
Cash and cash equivalents at end of year	349,561	335,768	327,706
Trustmark Corp (Parent Company Only) [Member]
Assets
Investment in banks	1,637,338	1,617,238
Other assets	16,975	17,349
Total Assets	1,654,313	1,634,587
Liabilities and Shareholders' Equity:
Accrued expense	1,004	1,030
Junior subordinated debt securities	61,856	61,856
Shareholders' equity	1,591,453	1,571,701
Total Liabilities and Shareholders' Equity	1,654,313	1,634,587
Revenue:
Dividends received from banks	128,592	65,663	65,987
Earnings of subsidiaries over distributions	23,791	42,211	44,756
Other income	86	71	60
Total Revenue	152,469	107,945	110,803
Expense:
Other expense	2,885	2,315	2,392
Total Expense	2,885	2,315	2,392
Net Income	149,584	105,630	108,411
Operating Activities
Net income	149,584	105,630	108,411
Adjustments to reconcile net income to net cash provided by operating activities:
Net change in investment in subsidiaries	(23,791)	(42,211)	(44,756)
Other	(1,395)	(1,697)	(739)
Net cash from operating activities	124,398	61,722	62,916
Investing Activities
Payment for investments in subsidiaries	0	(30,755)	0
Repayment for investments in subsidiaries		32,000
Net cash from investing activities	0	1,245	0
Financing Activities
Cash dividends paid on common stock	(62,425)	(62,795)	(62,666)
Other common stock transactions, net	(62,421)		(857)
Net cash from financing activities	(124,846)	(62,795)	(63,523)
Net change in cash and cash equivalents	(448)	172	(607)
Cash and cash equivalents at beginning of year	16,885	16,713	17,320
Cash and cash equivalents at end of year	$ 16,437	$ 16,885	$ 16,713