Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI - Summary of Loan Type Related to Each Balance in Allowance for Loan Losses (Details) - USD ($) $ in Thousands		Mar. 31, 2017	Dec. 31, 2016
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment		$ 39,100	$ 27,100
Total LHFI	[1]	8,004,657	7,851,213
Allowance for Loan Losses, LHFI [Member]
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment		39,083	27,075
LHFI, Collectively Evaluated For Impairment		7,965,574	7,824,138
Total LHFI		8,004,657	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		859,927	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		1,997	2,441
LHFI, Collectively Evaluated For Impairment		857,930	828,996
Total LHFI		859,927	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		1,656,837	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		4,792	4,649
LHFI, Collectively Evaluated For Impairment		1,652,045	1,655,394
Total LHFI		1,656,837	1,660,043
Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member]
Loans and Leases Receivable, Other Information [Abstract]
Total LHFI		2,064,352	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		9,191	6,219
LHFI, Collectively Evaluated For Impairment		2,055,161	2,027,957
Total LHFI		2,064,352	2,034,176
Other Real Estate Secured [Member] | Loans Secured by Real Estate [Member]
Loans and Leases Receivable, Other Information [Abstract]
Total LHFI		399,636	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		399,636	318,148
Total LHFI		399,636	318,148
Commercial and Industrial Loans [Member]
Loans and Leases Receivable, Other Information [Abstract]
Total LHFI		1,540,783	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		23,007	13,669
LHFI, Collectively Evaluated For Impairment		1,517,776	1,514,765
Total LHFI		1,540,783	1,528,434
Consumer Loans [Member]
Loans and Leases Receivable, Other Information [Abstract]
Total LHFI		166,314	170,562
Consumer Loans [Member] | Allowance for Loan Losses, LHFI [Member]
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment		1	2
LHFI, Collectively Evaluated For Impairment		166,313	170,560
Total LHFI		166,314	170,562
State and Other Political Subdivision Loans [Member]
Loans and Leases Receivable, Other Information [Abstract]
Total LHFI		910,493	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		910,493	917,515
Total LHFI		910,493	917,515
Other Loans [Member]
Loans and Leases Receivable, Other Information [Abstract]
Total LHFI		406,315	390,898
Other Loans [Member] | Allowance for Loan Losses, LHFI [Member]
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment		95	95
LHFI, Collectively Evaluated For Impairment		406,220	390,803
Total LHFI		$ 406,315	$ 390,898

[1] During the first quarter of 2017, Trustmark reclassified $36.7 million of acquired loans not accounted for under Financial Accounting Standards Board (FASB) Accounting Standard Codification (ASC) Topic 310-30, “Loans and Debt Securities Acquired with Deteriorated Credit Quality” to LHFI due to the discount on these loans being fully amortized.