Loans Held for Investment - Delinquencies (Details 6) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Other information concerning the credit quality
Totals	$ 3,095,540	$ 2,262,683	$ 2,167,547
Non-Accruing	5,734	3,970
Commercial and industrial
Other information concerning the credit quality
Totals	537,809	309,741	288,982
Non-Accruing	1,990	463
Franchise
Other information concerning the credit quality
Totals	431,618	328,925	295,965
Non-Accruing	0	1,630
Commercial owner occupied
Other information concerning the credit quality
Totals	460,068	294,726	302,556
Non-Accruing	606	536
SBA
Other information concerning the credit quality
Totals	92,195	62,256	70,191
Non-Accruing	503	0
Warehouse facilities
Other information concerning the credit quality
Totals	0	143,200	144,274
Non-Accruing		0
Commercial non-owner occupied
Other information concerning the credit quality
Totals	527,412	421,583	406,490
Non-Accruing	2,487	1,164
Multi-family
Other information concerning the credit quality
Totals	689,813	429,003	421,240
Non-Accruing	0	0
One-to-four family
Other information concerning the credit quality
Totals	101,377	80,050	78,781
Non-Accruing	131	155
Construction
Other information concerning the credit quality
Totals	231,098	169,748	141,293
Non-Accruing	0	0
Land
Other information concerning the credit quality
Totals	18,472	18,340	12,758
Non-Accruing	17	21
Other loans
Other information concerning the credit quality
Totals	5,678	5,111	$ 5,017
Non-Accruing	0	1
Current
Other information concerning the credit quality
Current	3,089,862	2,260,051
Current | Commercial and industrial
Other information concerning the credit quality
Current	535,709	309,464
Current | Franchise
Other information concerning the credit quality
Current	431,618	327,295
Current | Commercial owner occupied
Other information concerning the credit quality
Current	460,068	294,371
Current | SBA
Other information concerning the credit quality
Current	91,174	62,256
Current | Warehouse facilities
Other information concerning the credit quality
Current		143,200
Current | Commercial non-owner occupied
Other information concerning the credit quality
Current	524,925	421,369
Current | Multi-family
Other information concerning the credit quality
Current	689,813	429,003
Current | One-to-four family
Other information concerning the credit quality
Current	101,324	79,915
Current | Construction
Other information concerning the credit quality
Current	231,098	169,748
Current | Land
Other information concerning the credit quality
Current	18,455	18,319
Current | Other loans
Other information concerning the credit quality
Current	5,678	5,111
30-59
Other information concerning the credit quality
Days Past Due	1,042	323
30-59 | Commercial and industrial
Other information concerning the credit quality
Days Past Due	100	20
30-59 | Franchise
Other information concerning the credit quality
Days Past Due	0	0
30-59 | Commercial owner occupied
Other information concerning the credit quality
Days Past Due	0	0
30-59 | SBA
Other information concerning the credit quality
Days Past Due	928	0
30-59 | Warehouse facilities
Other information concerning the credit quality
Days Past Due		0
30-59 | Commercial non-owner occupied
Other information concerning the credit quality
Days Past Due	0	214
30-59 | Multi-family
Other information concerning the credit quality
Days Past Due	0	0
30-59 | One-to-four family
Other information concerning the credit quality
Days Past Due	14	89
30-59 | Construction
Other information concerning the credit quality
Days Past Due	0	0
30-59 | Land
Other information concerning the credit quality
Days Past Due	0	0
30-59 | Other loans
Other information concerning the credit quality
Days Past Due	0	0
60-89
Other information concerning the credit quality
Days Past Due	1,990	355
60-89 | Commercial and industrial
Other information concerning the credit quality
Days Past Due	1,990	0
60-89 | Franchise
Other information concerning the credit quality
Days Past Due	0	0
60-89 | Commercial owner occupied
Other information concerning the credit quality
Days Past Due	0	355
60-89 | SBA
Other information concerning the credit quality
Days Past Due	0	0
60-89 | Warehouse facilities
Other information concerning the credit quality
Days Past Due		0
60-89 | Commercial non-owner occupied
Other information concerning the credit quality
Days Past Due	0	0
60-89 | Multi-family
Other information concerning the credit quality
Days Past Due	0	0
60-89 | One-to-four family
Other information concerning the credit quality
Days Past Due	0	0
60-89 | Construction
Other information concerning the credit quality
Days Past Due	0	0
60-89 | Land
Other information concerning the credit quality
Days Past Due	0	0
60-89 | Other loans
Other information concerning the credit quality
Days Past Due	0	0
90
Other information concerning the credit quality
Days Past Due	2,646	1,954
90 | Commercial and industrial
Other information concerning the credit quality
Days Past Due	10	257
90 | Franchise
Other information concerning the credit quality
Days Past Due	0	1,630
90 | Commercial owner occupied
Other information concerning the credit quality
Days Past Due	0	0
90 | SBA
Other information concerning the credit quality
Days Past Due	93	0
90 | Warehouse facilities
Other information concerning the credit quality
Days Past Due		0
90 | Commercial non-owner occupied
Other information concerning the credit quality
Days Past Due	2,487	0
90 | Multi-family
Other information concerning the credit quality
Days Past Due	0	0
90 | One-to-four family
Other information concerning the credit quality
Days Past Due	39	46
90 | Construction
Other information concerning the credit quality
Days Past Due	0	0
90 | Land
Other information concerning the credit quality
Days Past Due	17	21
90 | Other loans
Other information concerning the credit quality
Days Past Due	$ 0	$ 0