Contingencies - Summary of Changes in ACL on Off-balance Sheet Credit Exposures (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Commitments And Contingencies Disclosure [Abstract]
Balance at beginning of period		$ 29,205	$ 36,421	$ 38,572	$ 0
FASB ASU 2016-13 adoption adjustment		0	0	0	29,638
PCL, off-balance sheet credit exposures	[1]	4,528	6,242	(4,839)	13,025
Balance at end of period		$ 33,733	$ 42,663	$ 33,733	$ 42,663

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