Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI - Additional Information (Details 2)	12 Months Ended
Dec. 31, 2019 USD ($) KeyRatio LoanPool CreditRiskGrade	Dec. 31, 2018 USD ($)
Financing Receivable, Recorded Investment, Aging [Abstract]
Number of key quality ratios \| KeyRatio	6
LHFS past due 90 days or more	$ 41,600,000	$ 37,400,000
Financing Receivable [Abstract]
Number of primary commercial loan groups \| LoanPool	9
Number of individual credit risk grades \| CreditRiskGrade	10
Minimum [Member]
Financing Receivable [Abstract]
Period to conduct asset review	6 months
Credit amount used as baseline in evaluating loan policy	$ 100,000
Maximum [Member]
Financing Receivable [Abstract]
Period to conduct asset review	18 months

Loans held for sale eligible for repurchase that are equal to or greater than 90 days past due.

No definition available.

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Credit amount used in baseline evaluation.

No definition available.

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Financing Receivable [Abstract]

No definition available.

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This line item represents the number of individual credit risk grades established by the entity.

No definition available.

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This line item represents the number of key quality ratios on which entity's loan portfolio credit quality indicators focused.

No definition available.

Name:	trmk_NumberOfKeyQualityRatios
Namespace Prefix:	trmk_
Data Type:	xbrli:integerItemType
Balance Type:	na
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This line item represents the number of primary commercial loan groups.

No definition available.

Name:	trmk_NumberOfPrimaryCommercialLoanGroups
Namespace Prefix:	trmk_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

This line item represents the period to conduct asset review by the entity.

No definition available.

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Namespace Prefix:	trmk_
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Balance Type:	na
Period Type:	duration

No definition available.

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Balance Type:	na
Period Type:	duration

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