LHFI and Allowance for Loan Losses, LHFI - Summary of Loan Type Related to Each Balance in Allowance for Loan Losses (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment		$ 48,900	$ 27,100
Total LHFI	[1]	8,569,967	7,851,213
Allowance for Loan Losses, LHFI [Member]
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment		48,936	27,075
LHFI, Collectively Evaluated For Impairment		8,521,031	7,824,138
Total LHFI		8,569,967	7,851,213
Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member]
Loans and Leases Receivable, Other Information [Abstract]
Total LHFI		987,624	831,437
Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member] | Allowance for Loan Losses, LHFI [Member]
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment		1,405	2,441
LHFI, Collectively Evaluated For Impairment		986,219	828,996
Total LHFI		987,624	831,437
Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member]
Loans and Leases Receivable, Other Information [Abstract]
Total LHFI		1,675,311	1,660,043
Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member] | Allowance for Loan Losses, LHFI [Member]
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment		4,736	4,649
LHFI, Collectively Evaluated For Impairment		1,670,575	1,655,394
Total LHFI		1,675,311	1,660,043
Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member]
Loans and Leases Receivable, Other Information [Abstract]
Total LHFI		2,193,823	2,034,176
Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member] | Allowance for Loan Losses, LHFI [Member]
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment		10,423	6,219
LHFI, Collectively Evaluated For Impairment		2,183,400	2,027,957
Total LHFI		2,193,823	2,034,176
Other Real Estate Secured [Member] | Loans Secured by Real Estate [Member]
Loans and Leases Receivable, Other Information [Abstract]
Total LHFI		517,956	318,148
Other Real Estate Secured [Member] | Loans Secured by Real Estate [Member] | Allowance for Loan Losses, LHFI [Member]
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Collectively Evaluated For Impairment		517,956	318,148
Total LHFI		517,956	318,148
Commercial and Industrial Loans [Member]
Loans and Leases Receivable, Other Information [Abstract]
Total LHFI		1,570,345	1,528,434
Commercial and Industrial Loans [Member] | Allowance for Loan Losses, LHFI [Member]
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment		31,799	13,669
LHFI, Collectively Evaluated For Impairment		1,538,546	1,514,765
Total LHFI		1,570,345	1,528,434
Consumer Loans [Member]
Loans and Leases Receivable, Other Information [Abstract]
Total LHFI		171,918	170,562
Consumer Loans [Member] | Allowance for Loan Losses, LHFI [Member]
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment		17	2
LHFI, Collectively Evaluated For Impairment		171,901	170,560
Total LHFI		171,918	170,562
State and Other Political Subdivision Loans [Member]
Loans and Leases Receivable, Other Information [Abstract]
Total LHFI		952,483	917,515
State and Other Political Subdivision Loans [Member] | Allowance for Loan Losses, LHFI [Member]
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Collectively Evaluated For Impairment		952,483	917,515
Total LHFI		952,483	917,515
Other Loans [Member]
Loans and Leases Receivable, Other Information [Abstract]
Total LHFI		500,507	390,898
Other Loans [Member] | Allowance for Loan Losses, LHFI [Member]
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment		556	95
LHFI, Collectively Evaluated For Impairment		499,951	390,803
Total LHFI		$ 500,507	$ 390,898

[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.