Shareholders' Equity (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014	Dec. 31, 2014
Securities available for sale and transferred securities, Before tax amount: [Abstract]
Unrealized holding gains arising during the period, Before tax amount	$ 18,438		$ 6,848
Reclassification adjustment for net gains realized in net income, Before tax amount	0		(389)
Change in net unrealized holding loss on securities transferred to held to maturity, Before tax amount	1,415		1,333
Total securities available for sale and transferred securities, Before tax amount	19,853		7,792
Securities available for sale and transferred securities, Tax (expense) benefit: [Abstract]
Unrealized holding gains arising during the period, Tax Effect	(7,052)		(2,619)
Reclassification adjustment for net gains realized in net income, Tax	0		149
Change in net unrealized holding loss on securities transferred to held to maturity, Tax	(541)		(510)
Total securities available for sale and transferred securities, Tax	(7,593)		(2,980)
Securities available for sale and transferred securities, Net of tax amount: [Abstract]
Unrealized holding gains arising during the period, after tax income (expense)	11,386		4,229
Reclassification adjustment for net gains realized in net income, after tax income (expense)	0		(240)
Change in net unrealized holding loss on securities transferred to held to maturity, after tax income (expense)	874		823
Total securities available for sale and transferred securities, after tax income (expense)	12,260		4,812
Pension and other postretirement benefit plans, Before tax amount: [Abstract]
Net change in prior service costs, before tax amount	63		63
Recognized net loss due to lump sum settlements, before tax amount	417		375
Change in net actuarial loss, before tax amount	1,220		906
Total pension and other postretirement benefit plans, before tax amount	1,700		1,344
Pension and other postretirement benefit plans, Tax (expense) benefit: [Abstract]
Net change in prior service costs, tax (expense) benefit	(24)		(24)
Recognized net loss due to lump sum settlements, tax (expense) benefit	(160)		(143)
Change in net actuarial loss, tax (expense) benefit	(466)		(347)
Total pension and other postretirement benefit plans, tax (expense) benefit	(650)		(514)
Pension and other postretirement benefit plans, Net of tax amount: [Abstract]
Net change in prior service costs, after tax income (expense)	39		39
Recognized net loss due to lump sum settlements, after tax income (expense)	257		232
Change in net actuarial loss, after tax income (expense)	754		559
Total pension and other postretirement benefit plans, after tax income (expense)	1,050		830
Derivatives, Before tax amount: [Abstract]
Change in accumulated gain on effective cash flow hedge derivatives, before tax amount	(985)		(661)
Reclassification adjustment for loss realized in net income, before tax amount	211
Total cash flow hedge derivatives, before tax benefit	(774)
Derivatives, Tax (expense) benefit: [Abstract]
Change in accumulated gain on effective cash flow hedge derivatives, tax (expense) benefit	377		253
Reclassification adjustment for loss realized in net income, tax (expense) benefit	(81)
Total cash flow hedge derivatives, tax (expense) benefit	296
Derivatives, Net of tax amount: [Abstract]
Change in the accumulated gain on effective cash flow hedge derivatives, after tax amount	(608)		(408)
Reclassification adjustment for loss realized in net income, after tax amount	130		0
Total cash flow hedge derivatives, after tax amount	(478)
Total other comprehensive income (loss), Before tax amount	20,779		8,475
Total other comprehensive income (loss), Tax expense (benefit)	(7,947)		(3,241)
Total other comprehensive income (loss), Net of tax	12,832		5,234
Accumulated Other Comprehensive Income (Loss) [Line Items]
Opening balance	(42,484)		(43,731)
Other comprehensive income (loss) before reclassification	12,702		5,474
Amounts reclassified from accumulated other comprehensive loss	130		(240)
Net other comprehensive income (loss)	12,832		5,234
Ending balance	(29,652)		(38,497)
Securities Available for Sale and Transferred Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Opening balance	(11,003)		(25,462)
Other comprehensive income (loss) before reclassification	12,260		5,052
Amounts reclassified from accumulated other comprehensive loss	0		(240)
Net other comprehensive income (loss)	12,260		4,812
Ending balance	1,257		(20,650)
Defined Benefit Pension Items [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Opening balance	(31,617)		(19,793)
Other comprehensive income (loss) before reclassification	1,050		830
Amounts reclassified from accumulated other comprehensive loss	0		0
Net other comprehensive income (loss)	1,050		830
Ending balance	(30,567)		(18,963)
Cash Flow Hedge Derivatives [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Opening balance	136		1,524
Other comprehensive income (loss) before reclassification	(608)		(408)
Amounts reclassified from accumulated other comprehensive loss	130		0
Net other comprehensive income (loss)	(478)		(408)
Ending balance	(342)		1,116
Trustmark Corporation [Member] | Tier 1 Capital (to Risk Weighted Assets) [Member]
Common Equity Tier One Risk Based Capital [Abstract]
Actual Regulatory Capital Amount	1,117,340			1,069,630
Actual Regulatory Capital Ratio (in hundredths)	13.14%			12.75%
Minimum Regulatory Capital Required Ratio (in hundredths)	4.50%				[1]
Minimum Regulatory Provision to be Well-Capitalized Ratio (in hundredths)		[1]			[1]
Tier 1 Capital (to Risk Weighted Assets) [Abstract]
Actual Regulatory Capital Amount	1,175,578			1,129,630
Actual Regulatory Capital Ratio (in hundredths)	13.83%			13.47%
Minimum Regulatory Capital Required Ratio (in hundredths)	6.00%			4.00%
Minimum Regulatory Provision to be Well-Capitalized Ratio (in hundredths)		[1]			[1]
Trustmark Corporation [Member] | Total Capital (to Risk Weighted Assets) [Member]
Total Capital (to Risk Weighted Assets) [Abstract]
Actual Regulatory Capital Amount	1,268,725			1,221,292
Actual Regulatory Capital Ratio (in hundredths)	14.92%			14.56%
Minimum Regulatory Capital Required Ratio (in hundredths)	8.00%			8.00%
Minimum Regulatory Provision to be Well-Capitalized Ratio (in hundredths)		[1]			[1]
Trustmark Corporation [Member] | Tier 1 Capital (to Average Assets) [Member]
Tier 1 Leverage (to Average Assets) [Abstract]
Actual Regulatory Capital Amount	1,175,578			1,129,630
Actual Regulatory Capital Ratio (in hundredths)	9.99%			9.63%
Minimum Regulatory Capital Required Ratio (in hundredths)	4.00%			4.00%
Minimum Regulatory Provision to be Well-Capitalized Ratio (in hundredths)		[1]			[1]
Trustmark National Bank [Member] | Tier 1 Capital (to Risk Weighted Assets) [Member]
Common Equity Tier One Risk Based Capital [Abstract]
Actual Regulatory Capital Amount	1,156,239			1,108,399
Actual Regulatory Capital Ratio (in hundredths)	13.60%			13.24%
Minimum Regulatory Capital Required Ratio (in hundredths)	4.50%				[1]
Minimum Regulatory Provision to be Well-Capitalized Ratio (in hundredths)	6.50%				[1]
Tier 1 Capital (to Risk Weighted Assets) [Abstract]
Actual Regulatory Capital Amount	1,156,239			1,108,399
Actual Regulatory Capital Ratio (in hundredths)	13.60%			13.24%
Minimum Regulatory Capital Required Ratio (in hundredths)	6.00%			4.00%
Minimum Regulatory Provision to be Well-Capitalized Ratio (in hundredths)	8.00%			6.00%
Trustmark National Bank [Member] | Total Capital (to Risk Weighted Assets) [Member]
Total Capital (to Risk Weighted Assets) [Abstract]
Actual Regulatory Capital Amount	1,249,386			1,198,697
Actual Regulatory Capital Ratio (in hundredths)	14.70%			14.32%
Minimum Regulatory Capital Required Ratio (in hundredths)	8.00%			8.00%
Minimum Regulatory Provision to be Well-Capitalized Ratio (in hundredths)	10.00%			10.00%
Trustmark National Bank [Member] | Tier 1 Capital (to Average Assets) [Member]
Tier 1 Leverage (to Average Assets) [Abstract]
Actual Regulatory Capital Amount	$ 1,156,239			$ 1,108,399
Actual Regulatory Capital Ratio (in hundredths)	9.84%			9.46%
Minimum Regulatory Capital Required Ratio (in hundredths)	4.00%			4.00%
Minimum Regulatory Provision to be Well-Capitalized Ratio (in hundredths)	5.00%			5.00%

[1] n/a