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, 2021	Dec. 31, 2020	Sep. 30, 2020
Financing Receivable Modifications [Line Items]
Nonaccrual	$ 66,240	$ 63,128
Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	5,629	5,985
Other Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	3,204	4,487
Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	13,077	15,197
Secured by 1-4 Family Residential Properties [Member] | Other Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	12,562	11,807
Commercial and Industrial Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	22,218	15,618
Consumer Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	60	86
State and Other Political Subdivision Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	3,786	3,970
Other Commercial Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	5,529	$ 5,793
Troubled Debt Restructurings [Member]
Financing Receivable Modifications [Line Items]
Accruing	2,394		$ 1,534
Nonaccrual	21,096		23,856
Total	23,490		25,390
Troubled Debt Restructurings [Member] | Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Accruing	0
Nonaccrual	4,607		13
Total	4,607		13
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		18
Nonaccrual	1,007		3,689
Total	1,007		3,707
Troubled Debt Restructurings [Member] | Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Accruing	394
Nonaccrual	2,961		2,970
Total	3,355		2,970
Troubled Debt Restructurings [Member] | Secured by 1-4 Family Residential Properties [Member] | Other Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Accruing	0
Nonaccrual	2,292
Total	2,292
Troubled Debt Restructurings [Member] | Commercial and Industrial Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing	2,000		1,500
Nonaccrual	1,600		13,198
Total	3,600		14,698
Troubled Debt Restructurings [Member] | Consumer Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing	0		16
Nonaccrual	11		19
Total	11		35
Troubled Debt Restructurings [Member] | State and Other Political Subdivision Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing	0
Nonaccrual	3,609		3,842
Total	3,609		3,842
Troubled Debt Restructurings [Member] | Other Commercial Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing	0
Nonaccrual	5,009		125
Total	$ 5,009		$ 125