Shareholders' Equity - Table of Actual Regulatory Capital Amounts and Ratios (Details) - USD ($) $ in Thousands		Sep. 30, 2018	Dec. 31, 2017
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		$ 1,302,859	$ 1,243,240
Actual Regulatory Capital Ratio		12.20%	11.77%
Minimum Regulatory Capital Required Ratio		6.375%	5.75%
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		$ 1,362,859	$ 1,303,238
Actual Regulatory Capital Ratio		12.76%	12.33%
Minimum Regulatory Capital Required Ratio		7.875%	7.25%
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		$ 1,453,447	$ 1,384,050
Actual Regulatory Capital Ratio		13.61%	13.10%
Minimum Regulatory Capital Required Ratio		9.875%	9.25%
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		$ 1,362,859	$ 1,303,238
Actual Regulatory Capital Ratio		10.41%	9.67%
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		$ 1,344,029	$ 1,284,575
Actual Regulatory Capital Ratio		12.59%	12.16%
Minimum Regulatory Capital Required Ratio		6.375%	5.75%
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		$ 1,344,029	$ 1,284,575
Actual Regulatory Capital Ratio		12.59%	12.16%
Minimum Regulatory Capital Required Ratio		7.875%	7.25%
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		$ 1,434,617	$ 1,365,387
Actual Regulatory Capital Ratio		13.44%	12.93%
Minimum Regulatory Capital Required Ratio		9.875%	9.25%
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		$ 1,344,029	$ 1,284,575
Actual Regulatory Capital Ratio		10.29%	9.54%
Minimum Regulatory Capital Required Ratio		4.00%	4.00%
Minimum Regulatory Provision to be Well-Capitalized Ratio		5.00%	5.00%

[1] n/a