Parent Company Only Financial Information - Parent Only Financial Statements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Assets
Other assets	$ 532,389	$ 498,864
Total Assets	13,497,877	13,286,460	$ 13,797,953
Liabilities and Shareholders' Equity:
Junior subordinated debt securities	61,856	61,856
Shareholders' equity	1,660,702	1,591,453	1,571,701	$ 1,520,208
Total Liabilities and Shareholders' Equity	13,497,877	13,286,460
Expense:
Net Income	150,460	149,584	105,630
Operating Activities
Net income	150,460	149,584	105,630
Adjustments to reconcile net income to net cash provided by operating activities:
Other	23,838	(6,886)	2,121
Net cash from operating activities	116,447	239,198	206,607
Investing Activities
Net cash from investing activities	(74,239)	438,787	(348,862)
Financing Activities
Common stock dividends	(59,804)	(62,425)	(62,795)
Repurchase and retirement of common stock	(56,615)	(62,421)	0
Net cash from financing activities	(32,853)	(664,192)	150,317
Trustmark Corp (Parent Company Only) [Member]
Assets
Investment in banks	1,707,644	1,637,338
Other assets	15,778	16,975
Total Assets	1,723,422	1,654,313
Liabilities and Shareholders' Equity:
Accrued expense	864	1,004
Junior subordinated debt securities	61,856	61,856
Shareholders' equity	1,660,702	1,591,453
Total Liabilities and Shareholders' Equity	1,723,422	1,654,313
Revenue:
Dividends received from banks	120,297	128,592	65,663
Earnings of subsidiaries over distributions	32,971	23,791	42,211
Other income	90	86	71
Total Revenue	153,358	152,469	107,945
Expense:
Other expense	2,898	2,885	2,315
Total Expense	2,898	2,885	2,315
Net Income	150,460	149,584	105,630
Operating Activities
Net income	150,460	149,584	105,630
Adjustments to reconcile net income to net cash provided by operating activities:
Net change in investment in subsidiaries	(32,971)	(23,791)	(42,211)
Other	(1,800)	(1,395)	(1,697)
Net cash from operating activities	115,689	124,398	61,722
Investing Activities
Payment for investments in subsidiaries	0	0	(30,755)
Repayment for investments in subsidiaries			32,000
Net cash from investing activities	0	0	1,245
Financing Activities
Common stock dividends	(59,804)	(62,425)	(62,795)
Repurchase and retirement of common stock	(56,615)	(62,421)
Net cash from financing activities	(116,419)	(124,846)	(62,795)
Net change in cash and cash equivalents	(730)	(448)	172
Cash and cash equivalents at beginning of year	16,437	16,885	16,713
Cash and cash equivalents at end of year	$ 15,707	$ 16,437	$ 16,885