Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI - Impact of Modifications Classified as Troubled Debt Restructurings (Details) - Troubled Debt Restructurings [Member] $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) Contract	Sep. 30, 2017 USD ($) Contract	Sep. 30, 2018 USD ($) Contract	Sep. 30, 2017 USD ($) Contract
Troubled Debt Restructurings [Abstract]
Number of Contracts | Contract	12	8	38	26
Pre-Modification Outstanding Recorded Investment	$ 11,274	$ 13,038	$ 24,798	$ 14,791
Post-Modification Outstanding Recorded Investment	$ 10,183	$ 13,039	$ 23,249	$ 14,785
Secured by 1-4 Family Residential Properties [Member]
Troubled Debt Restructurings [Abstract]
Number of Contracts | Contract	3	1	19	17
Pre-Modification Outstanding Recorded Investment	$ 121	$ 112	$ 1,873	$ 1,280
Post-Modification Outstanding Recorded Investment	$ 121	$ 113	$ 1,432	$ 1,290
Secured by Nonfarm, Nonresidential Properties [Member]
Troubled Debt Restructurings [Abstract]
Number of Contracts | Contract		1		1
Pre-Modification Outstanding Recorded Investment		$ 426		$ 426
Post-Modification Outstanding Recorded Investment		$ 426		$ 426
Commercial and Industrial Loans [Member]
Troubled Debt Restructurings [Abstract]
Number of Contracts | Contract	9	6	15	7
Pre-Modification Outstanding Recorded Investment	$ 11,153	$ 12,500	$ 22,899	$ 12,744
Post-Modification Outstanding Recorded Investment	$ 10,062	$ 12,500	$ 21,791	$ 12,744
Construction, Land Development and Other Land [Member]
Troubled Debt Restructurings [Abstract]
Number of Contracts | Contract			1	1
Pre-Modification Outstanding Recorded Investment			$ 22	$ 341
Post-Modification Outstanding Recorded Investment			$ 22	$ 325
Consumer Loans [Member]
Troubled Debt Restructurings [Abstract]
Number of Contracts | Contract			3
Pre-Modification Outstanding Recorded Investment			$ 4
Post-Modification Outstanding Recorded Investment			$ 4