Parent Company Only Financial Information - Parent Only Financial Statements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Assets
Other assets	$ 532,442	$ 577,964
Total Assets	13,797,953	13,352,333	$ 12,678,896
Liabilities and Shareholders' Equity:
Junior subordinated debt securities	61,856	61,856
Shareholders' equity	1,571,701	1,520,208	1,473,057	$ 1,419,940
Total Liabilities and Shareholders' Equity	13,797,953	13,352,333
Expense:
Net Income	105,630	108,411	116,038
Operating Activities
Net income	105,630	108,411	116,038
Adjustments to reconcile net income to net cash provided by operating activities:
Other	6,430	2,932	5,043
Net cash provided by operating activities	206,607	148,337	172,539
Investing Activities
Net cash used in investing activities	(348,862)	(649,664)	(527,277)
Financing Activities
Cash dividends paid on common stock	(62,795)	(62,666)	(62,605)
Net cash provided by financing activities	150,317	551,282	316,516
Net change in cash and cash equivalents	8,062	49,955	(38,222)
Cash and cash equivalents at beginning of year	327,706	277,751	315,973
Cash and cash equivalents at end of year	335,768	327,706	277,751
Trustmark Corp (Parent Company Only) [Member]
Assets
Investment in banks	1,617,238	1,566,186
Other assets	17,349	16,756
Total Assets	1,634,587	1,582,942
Liabilities and Shareholders' Equity:
Accrued expense	1,030	878
Junior subordinated debt securities	61,856	61,856
Shareholders' equity	1,571,701	1,520,208
Total Liabilities and Shareholders' Equity	1,634,587	1,582,942
Revenue:
Dividends received from banks	65,663	65,987	64,752
Earnings of subsidiaries over distributions	42,211	44,756	53,562
Other income	71	60	55
Total Revenue	107,945	110,803	118,369
Expense:
Other expense	2,315	2,392	2,331
Total Expense	2,315	2,392	2,331
Net Income	105,630	108,411	116,038
Operating Activities
Net income	105,630	108,411	116,038
Adjustments to reconcile net income to net cash provided by operating activities:
Net change in investment in subsidiaries	(42,211)	(44,756)	(53,562)
Other	(1,697)	(739)	(761)
Net cash provided by operating activities	61,722	62,916	61,715
Investing Activities
Payment for investments in subsidiaries	30,755
Repayment for investments in subsidiaries	32,000
Net cash used in investing activities	1,245
Financing Activities
Cash dividends paid on common stock	(62,795)	(62,666)	(62,605)
Other common stock transactions, net		(857)	(211)
Net cash provided by financing activities	(62,795)	(63,523)	(62,816)
Net change in cash and cash equivalents	172	(607)	(1,101)
Cash and cash equivalents at beginning of year	16,713	17,320	18,421
Cash and cash equivalents at end of year	$ 16,885	$ 16,713	$ 17,320