Contingencies - Summary of Changes in ACL on Off-balance Sheet Credit Exposures (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Commitments and Contingencies Disclosure [Abstract]
Balance at beginning of period		$ 33,733	$ 42,663	$ 38,572	$ 0
FASB ASU 2016-13 adoption adjustment		0	0	0	29,638
PCL, off-balance sheet credit exposures	[1]	(1,049)	(3,004)	(5,888)	10,021
Balance at end of period		$ 32,684	$ 39,659	$ 32,684	$ 39,659

[1] During the second quarter of 2021, Trustmark reclassified its credit loss expense related to off-balance sheet credit exposures from noninterest expense to PCL, off-balance sheet credit exposures. Prior periods have been reclassified accordingly.