Shareholders' Equity - Table of Actual Regulatory Capital Amounts and Ratios (Details) $ in Thousands		Sep. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)
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		$ 1,439,365	$ 1,395,844
Actual Regulatory Capital Ratio		11.68%	11.62%
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		$ 1,499,365	$ 1,455,844
Actual Regulatory Capital Ratio		12.17	12.11
Minimum Regulatory Capital Required Ratio		8.50	8.50
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		$ 1,726,040	$ 1,696,794
Actual Regulatory Capital Ratio		14.01	14.12
Minimum Regulatory Capital Required Ratio		10.50	10.50
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		$ 1,499,365	$ 1,455,844
Actual Regulatory Capital Ratio		8.92	9.33
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		$ 1,505,242	$ 1,412,015
Actual Regulatory Capital Ratio		12.22%	11.75%
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		$ 1,505,242	$ 1,412,015
Actual Regulatory Capital Ratio		12.22	11.75
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		$ 1,608,930	$ 1,530,044
Actual Regulatory Capital Ratio		13.06	12.73
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		$ 1,505,242	$ 1,412,015
Actual Regulatory Capital Ratio		8.98	9.07
Minimum Regulatory Capital Required Ratio		4.00	4.00
Minimum Regulatory Provision to be Well-Capitalized Ratio		5.00	5.00

[1] n/a