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, 2017	Dec. 31, 2016	Mar. 31, 2016
Financing Receivable Modifications [Line Items]
Nonaccrual	$ 61,307	$ 49,234
Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	2,856	3,323
Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	20,537	20,329
Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	11,492	8,482
Commercial and Industrial Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	25,410	15,824
Consumer Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	325	300
Troubled Debt Restructurings [Member]
Financing Receivable Modifications [Line Items]
Accruing	0		$ 2,243
Nonaccrual	12,399	$ 14,400	6,945
Total	12,399		9,188
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	642		845
Total	642		845
Troubled Debt Restructurings [Member] | Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Accruing	0		1,444
Nonaccrual	3,070		2,086
Total	3,070		3,530
Troubled Debt Restructurings [Member] | Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Accruing	0		799
Nonaccrual	841		3,566
Total	841		4,365
Troubled Debt Restructurings [Member] | Commercial and Industrial Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing	0		0
Nonaccrual	7,845		448
Total	7,845		$ 448
Troubled Debt Restructurings [Member] | Consumer Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing	0
Nonaccrual	1
Total	$ 1