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		Jun. 30, 2017	Dec. 31, 2016
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment		$ 53,400	$ 27,100
Total LHFI	[1]	8,296,045	7,851,213
Allowance for Loan Losses, LHFI [Member]
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment		53,385	27,075
LHFI, Collectively Evaluated For Impairment		8,242,660	7,824,138
Total LHFI		8,296,045	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		922,029	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		1,980	2,441
LHFI, Collectively Evaluated For Impairment		920,049	828,996
Total LHFI		922,029	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		1,655,968	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		5,260	4,649
LHFI, Collectively Evaluated For Impairment		1,650,708	1,655,394
Total LHFI		1,655,968	1,660,043
Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member]
Loans and Leases Receivable, Other Information [Abstract]
Total LHFI		2,109,367	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		17,884	6,219
LHFI, Collectively Evaluated For Impairment		2,091,483	2,027,957
Total LHFI		2,109,367	2,034,176
Other Real Estate Secured [Member] | Loans Secured by Real Estate [Member]
Loans and Leases Receivable, Other Information [Abstract]
Total LHFI		432,208	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		432,208	318,148
Total LHFI		432,208	318,148
Commercial and Industrial Loans [Member]
Loans and Leases Receivable, Other Information [Abstract]
Total LHFI		1,635,000	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		23,737	13,669
LHFI, Collectively Evaluated For Impairment		1,611,263	1,514,765
Total LHFI		1,635,000	1,528,434
Consumer Loans [Member]
Loans and Leases Receivable, Other Information [Abstract]
Total LHFI		170,858	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		170,857	170,560
Total LHFI		170,858	170,562
State and Other Political Subdivision Loans [Member]
Loans and Leases Receivable, Other Information [Abstract]
Total LHFI		936,860	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		936,860	917,515
Total LHFI		936,860	917,515
Other Loans [Member]
Loans and Leases Receivable, Other Information [Abstract]
Total LHFI		433,755	390,898
Other Loans [Member] | Allowance for Loan Losses, LHFI [Member]
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment		4,523	95
LHFI, Collectively Evaluated For Impairment		429,232	390,803
Total LHFI		$ 433,755	$ 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.