Fair Value - Fair Value and the Contractual Principal Outstanding of the LHFS (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair value and the contractual principal outstanding of the LHFS [Abstract]
Fair value of LHFS	$ 337,752	$ 169,285
LHFS contractual principal outstanding	321,690	164,420
Fair value less unpaid principal	$ 16,062	$ 4,865

Fair value and the contractual principal outstanding of the LHFS [Abstract]

No definition available.

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- Definition

This item represents the difference between the aggregate fair value and the unpaid principal.

+ References

No definition available.

+ Details

Name:	trmk_FairValueLessUnpaidPrincipalNet
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Data Type:	xbrli:monetaryItemType
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- Definition

Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.

+ References

No definition available.

+ Details

Name:	us-gaap_LoansHeldForSaleFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This is the principal amount outstanding for loans which are in the process of being securitized as of the date of the statement of financial position (across all types of loans).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121570589&loc=d3e107314-111719

+ Details

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Period Type:	instant