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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period				$ 79,290
Provision for loan losses, LHFI		$ 2,486	$ 3,167	4,097	$ 7,128
Balance at end of period		80,399		80,399
Allowance for Loan Losses, LHFI [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period		79,005	81,235	79,290	76,733
Transfers	[1]		782		782
Loans charged-off		(2,937)	(3,421)	(6,970)	(5,963)
Recoveries		1,845	1,803	3,982	4,886
Net (charge-offs) recoveries		(1,092)	(1,618)	(2,988)	(1,077)
Provision for loan losses, LHFI		2,486	3,167	4,097	7,128
Balance at end of period		80,399	83,566	80,399	83,566
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				7,390	7,865
Transfers	[1]				573
Loans charged-off				(35)	(2)
Recoveries				577	536
Provision for loan losses, LHFI				(1,001)	(1,082)
Balance at end of period		6,931	7,890	6,931	7,890
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				8,641	10,874
Transfers	[1]				127
Loans charged-off				(281)	(1,302)
Recoveries				336	342
Provision for loan losses, LHFI				(337)	(379)
Balance at end of period		8,359	9,662	8,359	9,662
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				22,376	23,428
Transfers	[1]				103
Loans charged-off				(34)	(1,117)
Recoveries				30	36
Provision for loan losses, LHFI				1,876	1,552
Balance at end of period		24,248	24,002	24,248	24,002
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				3,450	2,790
Transfers	[1]				(68)
Recoveries				16	12
Provision for loan losses, LHFI				255	(355)
Balance at end of period		3,721	2,379	3,721	2,379
Allowance for Loan Losses, LHFI [Member] | Commercial and Industrial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period				27,359	22,851
Transfers	[1]				2
Loans charged-off				(2,831)	(178)
Recoveries				329	1,347
Provision for loan losses, LHFI				2,761	7,506
Balance at end of period		27,618	31,528	27,618	31,528
Allowance for Loan Losses, LHFI [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period				2,890	3,470
Transfers	[1]				45
Loans charged-off				(1,269)	(1,007)
Recoveries				954	1,037
Provision for loan losses, LHFI				673	(571)
Balance at end of period		3,248	2,974	3,248	2,974
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				990	789
Provision for loan losses, LHFI				(552)	(24)
Balance at end of period		438	765	438	765
Allowance for Loan Losses, LHFI [Member] | Other Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period				6,194	4,666
Loans charged-off				(2,520)	(2,357)
Recoveries				1,740	1,576
Provision for loan losses, LHFI				422	481
Balance at end of period		$ 5,836	$ 4,366	$ 5,836	$ 4,366

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