Shareholders' Equity - Table of Actual Regulatory Capital Amounts and Ratios (Details) - USD ($) $ in Thousands		Sep. 30, 2020	Dec. 31, 2019
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		$ 1,358,889	$ 1,312,668
Actual Regulatory Capital Ratio		11.36%	11.93%
Minimum Regulatory Capital Required Ratio		7.00%	7.00%
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		$ 1,418,889	$ 1,372,668
Actual Regulatory Capital Ratio		11.86	12.48
Minimum Regulatory Capital Required Ratio		8.50	8.50
Trustmark Corporation [Member] | Total Capital (to Risk Weighted Assets) [Member]
Total Capital (to Risk Weighted Assets) [Abstract]
Actual Regulatory Capital Amount		$ 1,541,261	$ 1,457,760
Actual Regulatory Capital Ratio		12.88	13.25
Minimum Regulatory Capital Required Ratio		10.50	10.50
Trustmark Corporation [Member] | Tier 1 Leverage (to Average Assets) [Member]
Tier 1 Leverage (to Average Assets) [Abstract]
Actual Regulatory Capital Amount		$ 1,418,889	$ 1,372,668
Actual Regulatory Capital Ratio		9.20	10.48
Minimum Regulatory Capital Required Ratio		4.00	4.00
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		$ 1,384,436	$ 1,352,893
Actual Regulatory Capital Ratio		11.57%	12.30%
Minimum Regulatory Capital Required Ratio		7.00%	7.00%
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		$ 1,384,436	$ 1,352,893
Actual Regulatory Capital Ratio		11.57	12.30
Minimum Regulatory Capital Required Ratio		8.50	8.50
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		$ 1,506,808	$ 1,437,985
Actual Regulatory Capital Ratio		12.60	13.07
Minimum Regulatory Capital Required Ratio		10.50	10.50
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		$ 1,384,436	$ 1,352,893
Actual Regulatory Capital Ratio		9.00	10.35
Minimum Regulatory Capital Required Ratio		4.00	4.00
Minimum Regulatory Provision to be Well-Capitalized Ratio		5.00	5.00

[1] n/a