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	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Financing Receivable Modifications [Line Items]
Nonaccrual	$ 59,030	$ 61,624
Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	1,144	2,218
Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	18,598	14,718
Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	7,757	9,621
Commercial and Industrial Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	25,313	23,938
Consumer Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	110	205
Other Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	963	1,402
Troubled Debt Restructurings [Member]
Financing Receivable Modifications [Line Items]
Accruing	1,347		$ 2,346
Nonaccrual	29,163	$ 16,700	33,617
Total	30,510		35,963
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	18		26
Total	18		26
Troubled Debt Restructurings [Member] | Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Accruing	101		563
Nonaccrual	3,373		3,052
Total	3,474		3,615
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	5,243		360
Total	5,243		360
Troubled Debt Restructurings [Member] | Commercial and Industrial Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing	1,246		1,783
Nonaccrual	20,262		29,636
Total	21,508		31,419
Troubled Debt Restructurings [Member] | Consumer Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing	0		0
Nonaccrual	23		3
Total	23		3
Troubled Debt Restructurings [Member] | Other Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing	0		0
Nonaccrual	244		540
Total	$ 244		$ 540