Mortgage Banking (Details) (USD $)	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Mortgage servicing rights [Abstract]
Balance at beginning of period	$ 64,358,000us-gaap_ServicingAssetAtFairValueAmount	$ 67,834,000us-gaap_ServicingAssetAtFairValueAmount
Origination of servicing assets	3,126,000	2,315,000
Change in fair value [Abstract]
Due to market changes	(2,368,000)	(723,000)
Due to runoff	(2,213,000)	(1,812,000)
Balance at end of period	62,903,000us-gaap_ServicingAssetAtFairValueAmount	67,614,000us-gaap_ServicingAssetAtFairValueAmount
Residential mortgage loans sold	233,000,000	184,900,000
Gains on sales of residential mortgage loans, before tax	3,700,000us-gaap_GainLossOnSaleOfMortgageLoans	1,800,000us-gaap_GainLossOnSaleOfMortgageLoans
Mortgage loans serviced for others	5,635,000,000trmk_MortgageLoansServicedForOthers		5,636,000,000trmk_MortgageLoansServicedForOthers
Period of put back response	60 days
Mortgage Loans on Real Estate [Line Items]
Total mortgage loans sold and serviced for others	5,634,965,000		5,636,249,000
Schedule of changes in the reserve for mortgage loan [Abstract]
Balance at beginning of period	1,170,000	1,050,000
Provision for putback expenses	0us-gaap_ProvisionForLoanLossesExpensed	150,000us-gaap_ProvisionForLoanLossesExpensed
Losses	0us-gaap_ProvisionForLoanAndLeaseLosses	(72,000)us-gaap_ProvisionForLoanAndLeaseLosses
Balance at end of period	1,170,000	1,128,000
Mortgage loan servicing representation and warranty expenses	0	150,000
Federal National Mortgage Association [Member]
Mortgage Loans on Real Estate [Line Items]
Total mortgage loans sold and serviced for others	3,588,326,000		3,579,987,000
Government National Mortgage Association [Member]
Mortgage Loans on Real Estate [Line Items]
Total mortgage loans sold and serviced for others	1,922,043,000		1,948,565,000
Federal Home Loan Mortgage Corporation [Member]
Mortgage Loans on Real Estate [Line Items]
Total mortgage loans sold and serviced for others	76,987,000		80,551,000
Other [Member]
Mortgage Loans on Real Estate [Line Items]
Total mortgage loans sold and serviced for others	$ 47,609,000		$ 27,146,000

The amount of mortgage loan servicing put back expenses from representations and warranties on loans sold.

No definition available.

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- Definition

Amount of loans that underlying mortgage loans sold and serviced for others on balance sheet date.

+ References

No definition available.

+ Details

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- Definition

Outstanding balance of underlying mortgage loans serviced for others.

+ References

No definition available.

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- Details

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- Definition

Increase during the reporting period in the cumulative value of servicing rights. This increase is the result of new servicing rights that are created when mortgages are sold or transferred. Excludes disposals of mortgage loans sold serviced released.

+ References

No definition available.

+ Details

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- Definition

The period of time the company is required to provide a response to put back requests.

+ References

No definition available.

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- Definition

The net increase or decrease in fair value as a result of changes in the assumptions or model used to calculate the fair value of servicing assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 50

-Section 50

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=7882072&loc=d3e122625-111746

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- Definition

The gains (losses) included in earnings that represent the difference between the sale price and the carrying value of loans made to finance real estate acquisitions. This element refers to the gain (loss) and not to the cash proceeds of the sale. This element is a noncash adjustment to net income when calculating net cash generated by operating activities using the indirect method.

+ References

+ Details

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- Definition

The carrying amount of mortgage loans on real estate that were sold during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 205

-SubTopic 10

-Section S99

-Paragraph 6

-Subparagraph (SX 210.5-04.(c) Schedule IV)

-URI http://asc.fasb.org/extlink&oid=27047687&loc=d3e5864-122674

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 29

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 948

-SubTopic 310

-Section S99

-Paragraph 1

-Subparagraph (SX 210.12-29.6)

-URI http://asc.fasb.org/extlink&oid=6589523&loc=d3e617274-123014

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- Definition

Amount of reserve for write-down of a mortgage loan on real estate.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 205

-SubTopic 10

-Section S99

-Paragraph 6

-Subparagraph (SX 210.5-04.(c) Schedule IV)

-URI http://asc.fasb.org/extlink&oid=27047687&loc=d3e5864-122674

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

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-Name Regulation S-X (SX)

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-Publisher FASB

-Name Accounting Standards Codification

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-Subparagraph (SX 210.12-29.7)

-URI http://asc.fasb.org/extlink&oid=6589523&loc=d3e617274-123014

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- Definition

Amount of expense related to estimated loss from loan and lease transactions.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

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-Subparagraph (SX 210.9-04.11)

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- Definition

Amount of expense related to loss from loan transactions.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 11

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

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-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

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- Definition

Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 50

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- Definition

The net increase or decrease in fair value as a result of changes in the inputs used to calculate the fair value of servicing assets.

+ References

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