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, 2018	Dec. 31, 2017
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment	$ 55,800	$ 48,900
Total LHFI	8,835,868	8,569,967
Allowance for Loan Losses, LHFI [Member]
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment	55,835	48,936
LHFI, Collectively Evaluated For Impairment	8,780,033	8,521,031
Total LHFI	8,835,868	8,569,967
Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member]
Loans and Leases Receivable, Other Information [Abstract]
Total LHFI	1,056,601	987,624
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	1,552	1,405
LHFI, Collectively Evaluated For Impairment	1,055,049	986,219
Total LHFI	1,056,601	987,624
Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member]
Loans and Leases Receivable, Other Information [Abstract]
Total LHFI	1,825,492	1,675,311
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	3,963	4,736
LHFI, Collectively Evaluated For Impairment	1,821,529	1,670,575
Total LHFI	1,825,492	1,675,311
Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member]
Loans and Leases Receivable, Other Information [Abstract]
Total LHFI	2,220,914	2,193,823
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	9,476	10,423
LHFI, Collectively Evaluated For Impairment	2,211,438	2,183,400
Total LHFI	2,220,914	2,193,823
Other Real Estate Secured [Member] | Loans Secured by Real Estate [Member]
Loans and Leases Receivable, Other Information [Abstract]
Total LHFI	543,820	517,956
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, Individually Evaluated For Impairment	248
LHFI, Collectively Evaluated For Impairment	543,572	517,956
Total LHFI	543,820	517,956
Commercial and Industrial Loans [Member]
Loans and Leases Receivable, Other Information [Abstract]
Total LHFI	1,538,715	1,570,345
Commercial and Industrial Loans [Member] | Allowance for Loan Losses, LHFI [Member]
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment	30,717	31,799
LHFI, Collectively Evaluated For Impairment	1,507,998	1,538,546
Total LHFI	1,538,715	1,570,345
Consumer Loans [Member]
Loans and Leases Receivable, Other Information [Abstract]
Total LHFI	182,448	171,918
Consumer Loans [Member] | Allowance for Loan Losses, LHFI [Member]
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment	2	17
LHFI, Collectively Evaluated For Impairment	182,446	171,901
Total LHFI	182,448	171,918
State and Other Political Subdivision Loans [Member]
Loans and Leases Receivable, Other Information [Abstract]
Total LHFI	973,818	952,483
State and Other Political Subdivision Loans [Member] | Allowance for Loan Losses, LHFI [Member]
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment	8,595
LHFI, Collectively Evaluated For Impairment	965,223	952,483
Total LHFI	973,818	952,483
Other Loans [Member]
Loans and Leases Receivable, Other Information [Abstract]
Total LHFI	494,060	500,507
Other Loans [Member] | Allowance for Loan Losses, LHFI [Member]
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment	1,282	556
LHFI, Collectively Evaluated For Impairment	492,778	499,951
Total LHFI	$ 494,060	$ 500,507