Loans Held for Investment - Delinquencies (Details 6) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015
Other information concerning the credit quality
Totals	$ 2,927,554	$ 2,262,683	$ 2,118,323
Non-Accruing	4,062	3,970
Commercial and industrial
Other information concerning the credit quality
Totals	508,141	309,741	284,873
Non-Accruing	1,220	463
Franchise
Other information concerning the credit quality
Totals	403,855	328,925	257,582
Non-Accruing	1,461	1,630
Commercial owner occupied
Other information concerning the credit quality
Totals	443,060	294,726	294,545
Non-Accruing	486	536
SBA
Other information concerning the credit quality
Totals	86,076	62,256	50,306
Non-Accruing	329	0
Warehouse facilities
Other information concerning the credit quality
Totals	0	143,200	198,113
Non-Accruing		0
Commercial non-owner occupied
Other information concerning the credit quality
Totals	526,362	421,583	402,786
Non-Accruing	411	1,164
Multi-family
Other information concerning the credit quality
Totals	613,573	429,003	400,237
Non-Accruing	0	0
One-to-four family
Other information concerning the credit quality
Totals	106,538	80,050	84,283
Non-Accruing	137	155
Construction
Other information concerning the credit quality
Totals	215,786	169,748	124,448
Non-Accruing	0	0
Land
Other information concerning the credit quality
Totals	18,341	18,340	16,339
Non-Accruing	18	21
Other loans
Other information concerning the credit quality
Totals	5,822	5,111	$ 4,811
Non-Accruing	0	1
Current
Other information concerning the credit quality
Current	2,922,126	2,260,051
Current | Commercial and industrial
Other information concerning the credit quality
Current	506,965	309,464
Current | Franchise
Other information concerning the credit quality
Current	402,394	327,295
Current | Commercial owner occupied
Other information concerning the credit quality
Current	443,060	294,371
Current | SBA
Other information concerning the credit quality
Current	85,830	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	523,875	421,369
Current | Multi-family
Other information concerning the credit quality
Current	613,573	429,003
Current | One-to-four family
Other information concerning the credit quality
Current	106,498	79,915
Current | Construction
Other information concerning the credit quality
Current	215,786	169,748
Current | Land
Other information concerning the credit quality
Current	18,323	18,319
Current | Other loans
Other information concerning the credit quality
Current	5,822	5,111
30-59
Other information concerning the credit quality
Days Past Due	1,144	323
30-59 | Commercial and industrial
Other information concerning the credit quality
Days Past Due	1,144	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	0	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	0	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	2,487	355
60-89 | Commercial and industrial
Other information concerning the credit quality
Days Past Due	0	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	2,487	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	1,797	1,954
90 | Commercial and industrial
Other information concerning the credit quality
Days Past Due	32	257
90 | Franchise
Other information concerning the credit quality
Days Past Due	1,461	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	246	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	0	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	40	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	18	21
90 | Other loans
Other information concerning the credit quality
Days Past Due	$ 0	$ 0