Borrowings - Junior Subordinated Debt Securities - Additional information (Details) $ in Thousands		12 Months Ended
	Aug. 18, 2006 USD ($) Quarter	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Variable Interest Entity [Line Items]
Junior subordinated debt securities		$ 61,856	$ 61,856
Total assets		13,797,953	13,352,333	$ 12,678,896
Total liabilities and shareholders' equity		13,797,953	13,352,333
Common securities		14,115	14,091
Net income		$ 105,630	108,411	116,038
Trustmark Preferred Capital Trust I [Member] | Junior Subordinated Debt Securities [Member]
Variable Interest Entity [Line Items]
Face amount of debt issued	$ 60,000
Maturity date	Sep. 30, 2036
Variable interest rate, description		three-month LIBOR
Basis spread over LIBOR rate (in hundredths)	1.72%
Junior subordinated debt securities	$ 61,900
Consecutive quarters that Trustmark may defer interest payments | Quarter	20
Total assets		$ 61,900	61,900
Total liabilities and shareholders' equity		61,900	61,900
Trust preferred securities		60,000	60,000
Common securities		1,900	1,900
Net income		55	45	38
Dividends paid		$ 55	$ 45	$ 38