Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI - Change in Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period			$ 71,265
Provision for loan losses, LHFI	$ 2,921	$ 2,596	5,683	$ 4,839
Balance at end of period	76,184		76,184
Allowance for Loan Losses, LHFI [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	72,445	69,668	71,265	67,619
Loans charged-off	(2,118)	(3,251)	(6,320)	(6,614)
Recoveries	2,936	2,783	5,556	5,952
Net recoveries (charge-offs)	818	(468)	(764)	(662)
Provision for loan losses, LHFI	2,921	2,596	5,683	4,839
Balance at end of period	76,184	71,796	76,184	71,796
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)	(212)
Recoveries			753	657
Provision for loan losses, LHFI			(1,056)	(1,314)
Balance at end of period	8,724	10,718	8,724	10,718
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			(343)	(970)
Recoveries			904	566
Provision for loan losses, LHFI			(414)	(459)
Balance at end of period	10,494	9,815	10,494	9,815
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			(20)	(105)
Recoveries			236	802
Provision for loan losses, LHFI			3,467	2,090
Balance at end of period	24,650	24,350	24,650	24,350
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			26	3
Provision for loan losses, LHFI			905	284
Balance at end of period	3,194	2,754	3,194	2,754
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			(2,186)	(1,810)
Recoveries			869	318
Provision for loan losses, LHFI			1,186	3,628
Balance at end of period	21,880	17,951	21,880	17,951
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			(1,318)	(889)
Recoveries			978	1,822
Provision for loan losses, LHFI			413	(780)
Balance at end of period	3,314	3,032	3,314	3,032
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			(100)	104
Balance at end of period	759	913	759	913
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			(2,395)	(2,628)
Recoveries			1,790	1,784
Provision for loan losses, LHFI			1,282	1,286
Balance at end of period	$ 3,169	$ 2,263	$ 3,169	$ 2,263