LHFI and Allowance for Loan Losses, LHFI - Aging Analysis of Past Due and Nonaccrual LHFI by Loan Type (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		$ 18,433	$ 14,684
Nonaccrual		67,575	49,234
Current Loans		8,483,959	7,787,295
Total LHFI	[1]	8,569,967	7,851,213
Past Due 30 to 59 Days [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		12,390	9,686
Past Due 60 to 89 Days [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		3,872	3,167
Past Due 90 Days or More [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due	[2]	2,171	1,831
Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		392	339
Nonaccrual		2,105	3,323
Current Loans		985,127	827,775
Total LHFI		987,624	831,437
Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member] | Past Due 30 to 59 Days [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		391	248
Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member] | Past Due 60 to 89 Days [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		1	37
Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member] | Past Due 90 Days or More [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due	[2]		54
Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		10,413	9,178
Nonaccrual		19,022	20,329
Current Loans		1,645,876	1,630,536
Total LHFI		1,675,311	1,660,043
Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member] | Past Due 30 to 59 Days [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		6,412	5,308
Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member] | Past Due 60 to 89 Days [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		2,084	2,434
Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member] | Past Due 90 Days or More [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due	[2]	1,917	1,436
Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		2,575	706
Nonaccrual		12,608	8,482
Current Loans		2,178,640	2,024,988
Total LHFI		2,193,823	2,034,176
Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member] | Past Due 30 to 59 Days [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		2,319	606
Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member] | Past Due 60 to 89 Days [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		256	100
Other Real Estate Secured [Member] | Loans Secured by Real Estate [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due			179
Nonaccrual		212	402
Current Loans		517,744	317,567
Total LHFI		517,956	318,148
Other Real Estate Secured [Member] | Loans Secured by Real Estate [Member] | Past Due 30 to 59 Days [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due			179
Commercial and Industrial Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		2,004	784
Nonaccrual		33,338	15,824
Current Loans		1,535,003	1,511,826
Total LHFI		1,570,345	1,528,434
Commercial and Industrial Loans [Member] | Past Due 30 to 59 Days [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		759	571
Commercial and Industrial Loans [Member] | Past Due 60 to 89 Days [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		1,233	213
Commercial and Industrial Loans [Member] | Past Due 90 Days or More [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due	[2]	12
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		2,638	2,232
Nonaccrual		135	300
Current Loans		169,145	168,030
Total LHFI		171,918	170,562
Consumer Loans [Member] | Past Due 30 to 59 Days [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		2,141	1,561
Consumer Loans [Member] | Past Due 60 to 89 Days [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		255	330
Consumer Loans [Member] | Past Due 90 Days or More [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due	[2]	242	341
State and Other Political Subdivision Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		389	1,035
Current Loans		952,094	916,480
Total LHFI		952,483	917,515
State and Other Political Subdivision Loans [Member] | Past Due 30 to 59 Days [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		350	1,035
State and Other Political Subdivision Loans [Member] | Past Due 60 to 89 Days [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		39
Other Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		22	231
Nonaccrual		155	574
Current Loans		500,330	390,093
Total LHFI		500,507	390,898
Other Loans [Member] | Past Due 30 to 59 Days [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		18	178
Other Loans [Member] | Past Due 60 to 89 Days [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		$ 4	$ 53

[1] During the first quarter of 2017, Trustmark reclassified $36.7 million of acquired loans not accounted for under FASB ASC Topic 310-30 to LHFI due to the discount on these loans being fully amortized.

[2] Past due 90 days or more but still accruing interest.