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, 2016	Dec. 31, 2015	Sep. 30, 2015
Financing Receivable Modifications [Line Items]
Nonaccrual	$ 54,410	$ 55,312
Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	4,724	6,123
Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	20,107	23,079
Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	10,313	17,800
Commercial and Industrial Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	16,525	7,622
Consumer Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	189	31
Other Real Estate Secured [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	1,731	145
Troubled Debt Restructurings [Member]
Financing Receivable Modifications [Line Items]
Accruing			$ 2,204
Nonaccrual	3,669	$ 7,400	8,969
Total	3,669		11,173
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	556		1,006
Total	556		1,006
Troubled Debt Restructurings [Member] | Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Accruing			1,385
Nonaccrual	2,545		2,921
Total	2,545		4,306
Troubled Debt Restructurings [Member] | Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Accruing			819
Nonaccrual	179		4,503
Total	179		5,322
Troubled Debt Restructurings [Member] | Commercial and Industrial Loans [Member]
Financing Receivable Modifications [Line Items]
Accruing	0		0
Nonaccrual	387		477
Total	387		477
Troubled Debt Restructurings [Member] | Consumer Loans [Member]
Financing Receivable Modifications [Line Items]
Nonaccrual	2
Total	$ 2
Troubled Debt Restructurings [Member] | Other Real Estate Secured [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Modifications [Line Items]
Accruing			0
Nonaccrual			62
Total			$ 62