Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI - Nonaccrual LHFI by Loan Type (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Loan Portfolio [Abstract]
Total nonaccrual LHFI	$ 69,289	$ 49,234
Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member]
Loan Portfolio [Abstract]
Total nonaccrual LHFI	2,365	3,323
Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member]
Loan Portfolio [Abstract]
Total nonaccrual LHFI	18,593	20,329
Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member]
Loan Portfolio [Abstract]
Total nonaccrual LHFI	17,611	8,482
Other Real Estate Secured [Member] | Loans Secured by Real Estate [Member]
Loan Portfolio [Abstract]
Total nonaccrual LHFI	214	402
Commercial and Industrial Loans [Member]
Loan Portfolio [Abstract]
Total nonaccrual LHFI	25,101	15,824
Consumer Loans [Member]
Loan Portfolio [Abstract]
Total nonaccrual LHFI	607	300
Other Loans [Member]
Loan Portfolio [Abstract]
Total nonaccrual LHFI	$ 4,798	$ 574