Shareholders' Equity - Table of Actual Regulatory Capital Amounts and Ratios (Details) - USD ($) $ in Thousands		Dec. 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		$ 1,312,668	$ 1,271,538
Actual Regulatory Capital Ratio		11.93%	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		$ 1,372,668	$ 1,331,538
Actual Regulatory Capital Ratio		12.48%	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		$ 1,457,760	$ 1,412,059
Actual Regulatory Capital Ratio		13.25%	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		$ 1,372,668	$ 1,331,538
Actual Regulatory Capital Ratio		10.48%	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		$ 1,352,893	$ 1,311,548
Actual Regulatory Capital Ratio		12.30%	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		$ 1,352,893	$ 1,311,548
Actual Regulatory Capital Ratio		12.30%	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		$ 1,437,985	$ 1,392,069
Actual Regulatory Capital Ratio		13.07%	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		$ 1,352,893	$ 1,311,548
Actual Regulatory Capital Ratio		10.35%	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