Shareholders' Equity - Table of Actual Regulatory Capital Amounts and Ratios (Details) - USD ($) $ in Thousands		Mar. 31, 2019	Dec. 31, 2018
Trustmark Corporation [Member] | Common Equity Tier 1 Capital (to Risk Weighted Assets) [Member]
Common Equity Tier One Risk Based Capital [Abstract]
Actual Regulatory Capital Amount		$ 1,253,096	$ 1,271,538
Actual Regulatory Capital Ratio		11.88%	11.77%
Minimum Regulatory Capital Required Ratio		7.00%	6.375%
Minimum Regulatory Provision to be Well-Capitalized Ratio	[1]
Trustmark Corporation [Member] | Tier 1 Capital (to Risk Weighted Assets) [Member]
Tier 1 Capital (to Risk Weighted Assets) [Abstract]
Actual Regulatory Capital Amount		$ 1,313,096	$ 1,331,538
Actual Regulatory Capital Ratio		12.45%	12.33%
Minimum Regulatory Capital Required Ratio		8.50%	7.875%
Minimum Regulatory Provision to be Well-Capitalized Ratio	[1]
Trustmark Corporation [Member] | Total Capital (to Risk Weighted Assets) [Member]
Total Capital (to Risk Weighted Assets) [Abstract]
Actual Regulatory Capital Amount		$ 1,393,398	$ 1,412,059
Actual Regulatory Capital Ratio		13.21%	13.07%
Minimum Regulatory Capital Required Ratio		10.50%	9.875%
Minimum Regulatory Provision to be Well-Capitalized Ratio	[1]
Trustmark Corporation [Member] | Tier 1 Leverage (to Average Assets) [Member]
Tier 1 Leverage (to Average Assets) [Abstract]
Actual Regulatory Capital Amount		$ 1,313,096	$ 1,331,538
Actual Regulatory Capital Ratio		10.05%	10.26%
Minimum Regulatory Capital Required Ratio		4.00%	4.00%
Minimum Regulatory Provision to be Well-Capitalized Ratio	[1]
Trustmark National Bank [Member] | Common Equity Tier 1 Capital (to Risk Weighted Assets) [Member]
Common Equity Tier One Risk Based Capital [Abstract]
Actual Regulatory Capital Amount		$ 1,294,212	$ 1,311,548
Actual Regulatory Capital Ratio		12.27%	12.14%
Minimum Regulatory Capital Required Ratio		7.00%	6.375%
Minimum Regulatory Provision to be Well-Capitalized Ratio		6.50%	6.50%
Trustmark National Bank [Member] | Tier 1 Capital (to Risk Weighted Assets) [Member]
Tier 1 Capital (to Risk Weighted Assets) [Abstract]
Actual Regulatory Capital Amount		$ 1,294,212	$ 1,311,548
Actual Regulatory Capital Ratio		12.27%	12.14%
Minimum Regulatory Capital Required Ratio		8.50%	7.875%
Minimum Regulatory Provision to be Well-Capitalized Ratio		8.00%	8.00%
Trustmark National Bank [Member] | Total Capital (to Risk Weighted Assets) [Member]
Total Capital (to Risk Weighted Assets) [Abstract]
Actual Regulatory Capital Amount		$ 1,374,514	$ 1,392,069
Actual Regulatory Capital Ratio		13.03%	12.89%
Minimum Regulatory Capital Required Ratio		10.50%	9.875%
Minimum Regulatory Provision to be Well-Capitalized Ratio		10.00%	10.00%
Trustmark National Bank [Member] | Tier 1 Leverage (to Average Assets) [Member]
Tier 1 Leverage (to Average Assets) [Abstract]
Actual Regulatory Capital Amount		$ 1,294,212	$ 1,311,548
Actual Regulatory Capital Ratio		9.92%	10.13%
Minimum Regulatory Capital Required Ratio		4.00%	4.00%
Minimum Regulatory Provision to be Well-Capitalized Ratio		5.00%	5.00%

[1] n/a