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, 2020	Dec. 31, 2019	Jun. 30, 2019
Financing Receivable Modifications [Line Items]
Nonaccrual	$ 49,994	$ 53,226
Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	932	897
Other Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	4,441
Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	7,883	7,700
Commercial and Industrial Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	18,181	21,775
Consumer Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	120	108
State and Other Political Subdivision Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	4,049	4,079
Other Commercial Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	984
Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual		16,810
Other Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual		$ 825
Troubled Debt Restructurings [Member]
Financing Receivable Modifications [Line Items]
Accruing	1,589		$ 14,947
Nonaccrual	25,290		21,399
Total	26,879		36,346
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	14		20
Total	14		20
Troubled Debt Restructurings [Member] | Other Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Accruing	71
Nonaccrual	3,761
Total	3,832
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	3,010		5,311
Total	3,010		5,311
Troubled Debt Restructurings [Member] | Commercial and Industrial Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing	1,500		14,897
Nonaccrual	14,487		11,965
Total	15,987		26,862
Troubled Debt Restructurings [Member] | Consumer Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing	18		0
Nonaccrual	21		30
Total	39		30
Troubled Debt Restructurings [Member] | State and Other Political Subdivision Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing	0
Nonaccrual	3,872
Total	3,872
Troubled Debt Restructurings [Member] | Other Commercial Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing	0
Nonaccrual	125
Total	$ 125
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
Nonaccrual			3,563
Total			3,613
Troubled Debt Restructurings [Member] | Other Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing			0
Nonaccrual			510
Total			$ 510