Fair Value - Fair Value and the Contractual Principal Outstanding of the LHFS (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Fair value and the contractual principal outstanding of the LHFS [Abstract]
Fair value of LHFS	$ 134,874	$ 132,300
LHFS contractual principal outstanding	134,598	129,347
Fair value less unpaid principal	$ 276	$ 2,953

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

No definition available.

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Data Type:	xbrli:stringItemType
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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
Namespace Prefix:	trmk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- 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=109247956&loc=d3e107314-111719

+ Details

Name:	us-gaap_PrincipalAmountOutstandingOnLoansHeldForSaleOrSecuritization
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant