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, 2021	Dec. 31, 2020	Jun. 30, 2020
Financing Receivable Modifications [Line Items]
Nonaccrual	$ 51,448	$ 63,128
Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	6,165	5,985
Other Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	3,731	4,487
Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	13,563	15,197
Commercial and Industrial Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	6,042	15,618
Consumer Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	53	86
State and Other Political Subdivision Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	3,854	3,970
Other Commercial Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	5,643	$ 5,793
Troubled Debt Restructurings [Member]
Financing Receivable Modifications [Line Items]
Accruing	2,552		$ 1,589
Nonaccrual	22,563		25,290
Total	25,115		26,879
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	5,593		14
Total	5,593		14
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	0		71
Nonaccrual	1,160		3,761
Total	1,160		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	3,090		3,010
Total	3,090		3,010
Troubled Debt Restructurings [Member] | Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Accruing	52
Nonaccrual	2,414
Total	2,466
Troubled Debt Restructurings [Member] | Commercial and Industrial Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing	2,500		1,500
Nonaccrual	1,608		14,487
Total	4,108		15,987
Troubled Debt Restructurings [Member] | Consumer Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing	0		18
Nonaccrual	12		21
Total	12		39
Troubled Debt Restructurings [Member] | State and Other Political Subdivision Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing	0		0
Nonaccrual	3,677		3,872
Total	3,677		3,872
Troubled Debt Restructurings [Member] | Other Commercial Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing	0		0
Nonaccrual	5,009		125
Total	$ 5,009		$ 125