Defined Benefit and Other Postretirement Benefits - Plan Assets Measured at Fair Value (Details) - Trustmark Capital Accumulation Plan [Member] - Trustmark Corporation Pension Plan for Certain Employees of Acquired Financial Institutions [Member] - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Asset target allocations [Abstract]
Fair value of plan assets	$ 2,900	$ 2,873	$ 3,443
Level 1 [Member]
Asset target allocations [Abstract]
Fair value of plan assets	2,900	2,873
Money Market Funds [Member]
Asset target allocations [Abstract]
Fair value of plan assets	107	131
Money Market Funds [Member] | Level 1 [Member]
Asset target allocations [Abstract]
Fair value of plan assets	107	131
Exchange Traded Equity Securities Funds [Member]
Asset target allocations [Abstract]
Fair value of plan assets	1,460	1,242
Exchange Traded Equity Securities Funds [Member] | Level 1 [Member]
Asset target allocations [Abstract]
Fair value of plan assets	1,460	1,242
Exchange Traded Fixed Income Funds [Member]
Asset target allocations [Abstract]
Fair value of plan assets	1,021	1,182
Exchange Traded Fixed Income Funds [Member] | Level 1 [Member]
Asset target allocations [Abstract]
Fair value of plan assets	1,021	1,182
International Exchange Traded Funds [Member]
Asset target allocations [Abstract]
Fair value of plan assets	312	318
International Exchange Traded Funds [Member] | Level 1 [Member]
Asset target allocations [Abstract]
Fair value of plan assets	$ 312	$ 318