Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI - Impaired Financing Receivables (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Loan and Lease Receivables, Impaired [Abstract]
Total LHFI Unpaid Principal Balance	$ 53,677	$ 35,077
Total LHFI With No Related Allowance Recorded	29,588	19,440
Total LHFI With an Allowance Recorded	19,930	7,635
Total LHFI Carrying Amount	49,518	27,075
Related Allowance	7,421	3,260
Average Recorded Investment	38,297	29,140
Commercial and Industrial Loans [Member]
Loan and Lease Receivables, Impaired [Abstract]
Total LHFI Unpaid Principal Balance	24,250	14,593
Total LHFI With No Related Allowance Recorded	23,081	11,222
Total LHFI With an Allowance Recorded	419	2,447
Total LHFI Carrying Amount	23,500	13,669
Related Allowance	101	1,976
Average Recorded Investment	18,584	14,258
Consumer Loans [Member]
Loan and Lease Receivables, Impaired [Abstract]
Total LHFI Unpaid Principal Balance	1	2
Total LHFI With No Related Allowance Recorded	0	0
Total LHFI With an Allowance Recorded	1	2
Total LHFI Carrying Amount	1	2
Related Allowance	0	0
Average Recorded Investment	1	2
State and Other Political Subdivision Loans [Member]
Loan and Lease Receivables, Impaired [Abstract]
Total LHFI Unpaid Principal Balance	0	0
Total LHFI With No Related Allowance Recorded	0	0
Total LHFI With an Allowance Recorded	0	0
Total LHFI Carrying Amount	0	0
Related Allowance	0	0
Average Recorded Investment	0	0
Other Loans [Member]
Loan and Lease Receivables, Impaired [Abstract]
Total LHFI Unpaid Principal Balance	4,428	95
Total LHFI With No Related Allowance Recorded	0	0
Total LHFI With an Allowance Recorded	4,428	95
Total LHFI Carrying Amount	4,428	95
Related Allowance	657	0
Average Recorded Investment	2,262	95
Loans Secured by Real Estate [Member] | Construction, Land Development and Other Land [Member]
Loan and Lease Receivables, Impaired [Abstract]
Total LHFI Unpaid Principal Balance	2,758	5,691
Total LHFI With No Related Allowance Recorded	1,331	2,213
Total LHFI With an Allowance Recorded	200	228
Total LHFI Carrying Amount	1,531	2,441
Related Allowance	70	103
Average Recorded Investment	1,986	2,943
Loans Secured by Real Estate [Member] | Secured by 1-4 Family Residential Properties [Member]
Loan and Lease Receivables, Impaired [Abstract]
Total LHFI Unpaid Principal Balance	6,093	6,134
Total LHFI With No Related Allowance Recorded	175	221
Total LHFI With an Allowance Recorded	4,499	4,428
Total LHFI Carrying Amount	4,674	4,649
Related Allowance	1,243	960
Average Recorded Investment	4,662	4,639
Loans Secured by Real Estate [Member] | Secured by Nonfarm, Nonresidential Properties [Member]
Loan and Lease Receivables, Impaired [Abstract]
Total LHFI Unpaid Principal Balance	16,147	8,562
Total LHFI With No Related Allowance Recorded	5,001	5,784
Total LHFI With an Allowance Recorded	10,383	435
Total LHFI Carrying Amount	15,384	6,219
Related Allowance	5,350	221
Average Recorded Investment	10,802	6,703
Loans Secured by Real Estate [Member] | Other Real Estate Secured [Member]
Loan and Lease Receivables, Impaired [Abstract]
Total LHFI Unpaid Principal Balance	0	0
Total LHFI With No Related Allowance Recorded	0	0
Total LHFI With an Allowance Recorded	0	0
Total LHFI Carrying Amount	0	0
Related Allowance	0	0
Average Recorded Investment	$ 0	$ 500