LHFI and Allowance for Loan Losses, LHFI - Change in Allowance for Loan Losses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	$ 71,265
Provision for loan losses, LHFI	15,094	$ 10,957	$ 8,375
Balance at end of period	76,733	71,265
Allowance for Loan Losses, LHFI [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	71,265	67,619	69,616
Loans charged-off	(21,147)	(18,930)	(22,469)
Recoveries	11,521	11,619	12,097
Net (charge-offs) recoveries	(9,626)	(7,311)	(10,372)
Provision for loan losses, LHFI	15,094	10,957	8,375
Balance at end of period	76,733	71,265	67,619
Allowance for Loan Losses, LHFI [Member] | Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	9,085	11,587
Loans charged-off	(79)	(311)
Recoveries	1,428	1,380
Provision for loan losses, LHFI	(2,569)	(3,571)
Balance at end of period	7,865	9,085	11,587
Allowance for Loan Losses, LHFI [Member] | Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	10,347	10,678
Loans charged-off	(950)	(1,319)
Recoveries	1,833	1,122
Provision for loan losses, LHFI	(356)	(134)
Balance at end of period	10,874	10,347	10,678
Allowance for Loan Losses, LHFI [Member] | Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	20,967	21,563
Loans charged-off	(4,231)	(3,067)
Recoveries	396	976
Provision for loan losses, LHFI	6,296	1,495
Balance at end of period	23,428	20,967	21,563
Allowance for Loan Losses, LHFI [Member] | Other Real Estate Secured [Member] | Loans Secured by Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	2,263	2,467
Loans charged-off	(5)	(27)
Recoveries	69	7
Provision for loan losses, LHFI	463	(184)
Balance at end of period	2,790	2,263	2,467
Allowance for Loan Losses, LHFI [Member] | Commercial and Industrial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	22,011	15,815
Loans charged-off	(8,286)	(6,602)
Recoveries	2,578	732
Provision for loan losses, LHFI	6,548	12,066
Balance at end of period	22,851	22,011	15,815
Allowance for Loan Losses, LHFI [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	3,241	2,879
Loans charged-off	(2,546)	(1,864)
Recoveries	1,938	4,007
Provision for loan losses, LHFI	837	(1,781)
Balance at end of period	3,470	3,241	2,879
Allowance for Loan Losses, LHFI [Member] | State and Other Political Subdivision Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	859	809
Provision for loan losses, LHFI	(70)	50
Balance at end of period	789	859	809
Allowance for Loan Losses, LHFI [Member] | Other Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	2,492	1,821
Loans charged-off	(5,050)	(5,740)
Recoveries	3,279	3,395
Provision for loan losses, LHFI	3,945	3,016
Balance at end of period	$ 4,666	$ 2,492	$ 1,821