Represents the number of outstanding long-term FHLB advances.

No definition available.

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Namespace Prefix:	trmk_
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Balance Type:	na
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- Definition

Weighted average cost related to FHLB advances.

+ References

No definition available.

+ Details

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Data Type:	num:percentItemType
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- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

+ Details

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- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

+ Details

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- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Interest expense incurred during the reporting period on long-term borrowings associated with Federal Home Loan Bank and Federal Reserve Bank advances.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of addition (reduction) to the amount at which a liability could be incurred (settled) in a current transaction between willing parties.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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Borrowings - Long-term Debt Instruments - Additional information (Details) - Federal Home Loan Bank Advances [Member]	12 Months Ended
	Dec. 31, 2017 USD ($) Loan	Dec. 31, 2016 USD ($) Loan	Dec. 31, 2015 USD ($)
Dallas [Member]
Long-Term Borrowings [Abstract]
Number of outstanding long-term FHLB advances \| Loan	0	1
Weighted average remaining maturity		1 year 4 months 24 days
Weighted-average cost related to FHLB advances (in hundredths)		0.24%
Maturity date		May 25, 2018
Atlanta [Member]
Long-Term Borrowings [Abstract]
Number of outstanding long-term FHLB advances \| Loan	2	3
Weighted average remaining maturity	4 years 5 months 8 days	5 years 3 months 25 days
Weighted-average cost related to FHLB advances (in hundredths)	0.63%	0.82%
Atlanta [Member] \| Minimum [Member]
Long-Term Borrowings [Abstract]
Interest rate (in hundredths)	0.08%	0.08%
Atlanta [Member] \| Maximum [Member]
Long-Term Borrowings [Abstract]
Interest rate (in hundredths)	0.75%	6.12%
Atlanta and Dallas [Member]
Long-Term Borrowings [Abstract]
Interest expense, long-term	$ 566,000	$ 2,100,000	$ 49,000
Long Term Borrowing [Member] \| BancTrust [Member] \| Fair Market Value Adjustment [Member]
Long-Term Borrowings [Abstract]
Long-term FHLB advances	0	1,000
Long Term Borrowing [Member] \| Dallas [Member]
Long-Term Borrowings [Abstract]
Long-term FHLB advances		250,000,000
Long Term Borrowing [Member] \| Atlanta [Member] \| BancTrust [Member]
Long-Term Borrowings [Abstract]
Long-term FHLB advances	946,000	1,000,000
Long Term Borrowing [Member] \| Atlanta [Member] \| BancTrust [Member] \| Minimum [Member]
Long-Term Borrowings [Abstract]
Long-term FHLB advances	171,000	38,000
Long Term Borrowing [Member] \| Atlanta [Member] \| BancTrust [Member] \| Maximum [Member]
Long-Term Borrowings [Abstract]
Long-term FHLB advances	$ 775,000	$ 800,000