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, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period				$ 76,733
Provision for loan losses, LHFI		$ 3,167	$ 2,921	7,128	$ 5,683
Balance at end of period		83,566		83,566
Allowance for Loan Losses, LHFI [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period		81,235	72,445	76,733	71,265
Transfers	[1]	782		782
Loans charged-off		(3,421)	(2,118)	(5,963)	(6,320)
Recoveries		1,803	2,936	4,886	5,556
Net (charge-offs) recoveries		(1,618)	818	(1,077)	(764)
Provision for loan losses, LHFI		3,167	2,921	7,128	5,683
Balance at end of period		83,566	76,184	83,566	76,184
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				7,865	9,085
Transfers	[2]			573
Loans charged-off				(2)	(58)
Recoveries				536	753
Provision for loan losses, LHFI				(1,082)	(1,056)
Balance at end of period		7,890	8,724	7,890	8,724
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				10,874	10,347
Transfers	[2]			127
Loans charged-off				(1,302)	(343)
Recoveries				342	904
Provision for loan losses, LHFI				(379)	(414)
Balance at end of period		9,662	10,494	9,662	10,494
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				23,428	20,967
Transfers	[2]			103
Loans charged-off				(1,117)	(20)
Recoveries				36	236
Provision for loan losses, LHFI				1,552	3,467
Balance at end of period		24,002	24,650	24,002	24,650
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				2,790	2,263
Transfers	[2]			(68)
Recoveries				12	26
Provision for loan losses, LHFI				(355)	905
Balance at end of period		2,379	3,194	2,379	3,194
Allowance for Loan Losses, LHFI [Member] | Commercial and Industrial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period				22,851	22,011
Transfers	[2]			2
Loans charged-off				(178)	(2,186)
Recoveries				1,347	869
Provision for loan losses, LHFI				7,506	1,186
Balance at end of period		31,528	21,880	31,528	21,880
Allowance for Loan Losses, LHFI [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period				3,470	3,241
Transfers	[2]			45
Loans charged-off				(1,007)	(1,318)
Recoveries				1,037	978
Provision for loan losses, LHFI				(571)	413
Balance at end of period		2,974	3,314	2,974	3,314
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				789	859
Provision for loan losses, LHFI				(24)	(100)
Balance at end of period		765	759	765	759
Allowance for Loan Losses, LHFI [Member] | Other Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period				4,666	2,492
Loans charged-off				(2,357)	(2,395)
Recoveries				1,576	1,790
Provision for loan losses, LHFI				481	1,282
Balance at end of period		$ 4,366	$ 3,169	$ 4,366	$ 3,169

[1] The allowance for loan losses balance related to the remaining loans acquired in the Bay Bank & Trust Company (Bay Bank) merger on March 16, 2012, which were transferred from acquired loans to LHFI during the second quarter of 2018.

[2] The allowance for loan losses balance related to the remaining loans acquired in the Bay Bank merger on March 16, 2012, which were transferred from acquired loans to LHFI during the second quarter of 2018.