Acquired Loans - Components of the Allowance for Loan Losses on Acquired Loans (Details) - USD ($) $ in Thousands		3 Months Ended	9 Months Ended
		Sep. 30, 2019	Sep. 30, 2020		Sep. 30, 2019
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		$ 1,398	$ 815	[1]	$ 1,231
FASB ASU 2016-13 adoption adjustment			$ (815)
Net (charge-offs) recoveries		(9)			(26)
Provision for loan losses, acquired loans	[1]	(140)			44
Balance at end of period		$ 1,249			$ 1,249

[1] Effective January 1, 2020, Trustmark adopted FASB ASU 2016-13 using the modified retrospective approach.  Therefore, prior period balances are presented under legacy GAAP and may not be comparable to current period presentation.