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	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable Modifications [Line Items]
Nonaccrual	$ 53,226	$ 61,624
Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	897	2,218
Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	16,810	14,718
Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	7,700	9,621
Other Real Estate Secured [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	1,032	927
Commercial and Industrial Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	21,775	23,938
Consumer Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	108	205
Other Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	825	1,402
Troubled Debt Restructurings [Member]
Financing Receivable Modifications [Line Items]
Accruing	3,396	11,484	$ 660
Nonaccrual	28,127	16,706	23,211
Total	31,523	28,190	23,871
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	0
Nonaccrual	15	24	199
Total	15	24	199
Troubled Debt Restructurings [Member] | Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Accruing	77	743	51
Nonaccrual	3,865	3,125	3,140
Total	3,942	3,868	3,191
Troubled Debt Restructurings [Member] | Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Accruing	0	1,734	0
Nonaccrual	5,176	395	421
Total	5,176	2,129	421
Troubled Debt Restructurings [Member] | Commercial and Industrial Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing	3,319	9,007	53
Nonaccrual	18,913	12,620	19,434
Total	22,232	21,627	19,487
Troubled Debt Restructurings [Member] | Consumer Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing	0	0	0
Nonaccrual	21	2	17
Total	21	2	17
Troubled Debt Restructurings [Member] | Other Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing	0	0	556
Nonaccrual	137	540	0
Total	$ 137	$ 540	$ 556