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, 2020	Dec. 31, 2019	Sep. 30, 2019
Financing Receivable Modifications [Line Items]
Nonaccrual	$ 53,856	$ 53,226
Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	786	897
Other Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	4,298
Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	10,272	7,700
Commercial and Industrial Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	16,813	21,775
Consumer Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	96	108
State and Other Political Subdivision Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	4,019	4,079
Other Commercial Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	5,920
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	1,534		$ 1,347
Nonaccrual	23,856		29,163
Total	25,390		30,510
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	13		18
Total	13		18
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	18
Nonaccrual	3,689
Total	3,707
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	2,970		5,243
Total	2,970		5,243
Troubled Debt Restructurings [Member] | Commercial and Industrial Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing	1,500		1,246
Nonaccrual	13,198		20,262
Total	14,698		21,508
Troubled Debt Restructurings [Member] | Consumer Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing	16		0
Nonaccrual	19		23
Total	35		23
Troubled Debt Restructurings [Member] | State and Other Political Subdivision Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing	0
Nonaccrual	3,842
Total	3,842
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			101
Nonaccrual			3,373
Total			3,474
Troubled Debt Restructurings [Member] | Other Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing			0
Nonaccrual			244
Total			$ 244