Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI - Troubled Debt Restructuring Related to Loans Held for Investment, Excluding Covered Loans, by Loan Type (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Financing Receivable Modifications [Line Items]
Nonaccrual	$ 52,888	$ 61,624
Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	1,263	2,218
Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	17,591	14,718
Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	7,870	9,621
Commercial and Industrial Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	15,708	23,938
Consumer Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	152	205
Other Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	1,262	1,402
Troubled Debt Restructurings [Member]
Financing Receivable Modifications [Line Items]
Accruing	14,947		$ 1,234
Nonaccrual	21,399	$ 16,700	33,218
Total	36,346		34,452
Troubled Debt Restructurings [Member] | Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Accruing	0		0
Nonaccrual	20		208
Total	20		208
Troubled Debt Restructurings [Member] | Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Accruing	50		501
Nonaccrual	3,563		3,407
Total	3,613		3,908
Troubled Debt Restructurings [Member] | Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Accruing	0		0
Nonaccrual	5,311		370
Total	5,311		370
Troubled Debt Restructurings [Member] | Commercial and Industrial Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing	14,897		733
Nonaccrual	11,965		28,673
Total	26,862		29,406
Troubled Debt Restructurings [Member] | Consumer Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing	0		0
Nonaccrual	30		4
Total	30		4
Troubled Debt Restructurings [Member] | Other Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing	0		0
Nonaccrual	510		556
Total	$ 510		$ 556