Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI - Change in Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	$ 71,265
Provision for loan losses, LHFI	2,762	$ 2,243
Balance at end of period	72,445
Allowance for Loan Losses, LHFI [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	71,265	67,619
Loans charged-off	(4,202)	(3,363)
Recoveries	2,620	3,169
Net charge-offs	(1,582)	(194)
Provision for loan losses, LHFI	2,762	2,243
Balance at end of period	72,445	69,668
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	(58)
Recoveries	303	492
Provision for loan losses, LHFI	(804)	(1,937)
Balance at end of period	8,526	10,142
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	(241)	(692)
Recoveries	152	457
Provision for loan losses, LHFI	529	30
Balance at end of period	10,787	10,473
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		(27)
Recoveries	182	119
Provision for loan losses, LHFI	759	2,052
Balance at end of period	21,908	23,707
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
Recoveries	20	1
Provision for loan losses, LHFI	856	(395)
Balance at end of period	3,139	2,073
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	(1,984)	(770)
Recoveries	488	123
Provision for loan losses, LHFI	1,136	2,481
Balance at end of period	21,651	17,649
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	(745)	(484)
Recoveries	480	1,010
Provision for loan losses, LHFI	216	(601)
Balance at end of period	3,192	2,804
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	(11)	7
Balance at end of period	848	816
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	(1,174)	(1,390)
Recoveries	995	967
Provision for loan losses, LHFI	81	606
Balance at end of period	$ 2,394	$ 2,004