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	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Financing Receivable Modifications [Line Items]
Nonaccrual	$ 63,514	$ 63,128
Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	6,109	5,985
Other Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	3,964	4,487
Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	15,695	15,197
Commercial and Industrial Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	12,776	15,618
Consumer Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	71	86
State and Other Political Subdivision Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	3,914	3,970
Other Commercial Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	5,766	$ 5,793
Troubled Debt Restructurings [Member]
Financing Receivable Modifications [Line Items]
Accruing	1,542		$ 2,657
Nonaccrual	21,407		23,836
Total	22,949		26,493
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	11		14
Total	11		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	42		0
Nonaccrual	3,644		3,672
Total	3,686		3,672
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	3,846		2,899
Total	3,846		2,899
Troubled Debt Restructurings [Member] | Commercial and Industrial Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing	1,500		2,640
Nonaccrual	10,073		17,103
Total	11,573		19,743
Troubled Debt Restructurings [Member] | Consumer Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing	0		17
Nonaccrual	15		23
Total	15		40
Troubled Debt Restructurings [Member] | State and Other Political Subdivision Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing	0
Nonaccrual	3,737
Total	3,737
Troubled Debt Restructurings [Member] | Other Commercial Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing	0		0
Nonaccrual	81		125
Total	$ 81		$ 125