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	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Financing Receivable Modifications [Line Items]
Nonaccrual	$ 74,144	$ 49,234
Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	2,746	3,323
Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	19,079	20,329
Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	20,661	8,482
Commercial and Industrial Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	26,086	15,824
Consumer Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	491	300
Troubled Debt Restructurings [Member]
Financing Receivable Modifications [Line Items]
Accruing	0		$ 0
Nonaccrual	13,240	$ 14,400	7,704
Total	13,240		7,704
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	641		577
Total	641		577
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		0
Nonaccrual	3,589		3,187
Total	3,589		3,187
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	802		3,501
Total	802		3,501
Troubled Debt Restructurings [Member] | Commercial and Industrial Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing	0		0
Nonaccrual	8,207		437
Total	8,207		437
Troubled Debt Restructurings [Member] | Consumer Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing	0		0
Nonaccrual	1		2
Total	$ 1		$ 2