Loans Held for Investment - Delinquencies (Details 6) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Sep. 30, 2014
Other information concerning the credit quality
Totals	$ 2,857,775	$ 2,262,683	$ 2,130,853
Non-Accruing	4,823	3,970	4,663
Commercial and industrial
Other information concerning the credit quality
Totals	491,112	309,741	276,321	$ 276,321
Non-Accruing	498	463	601
Franchise
Other information concerning the credit quality
Totals	371,875	328,925	216,544
Non-Accruing	1,630	1,630	1,854
Commercial owner occupied
Other information concerning the credit quality
Totals	424,289	294,726	279,704
Non-Accruing	839	536	527
SBA
Other information concerning the credit quality
Totals	78,350	62,256	49,855
Non-Accruing	69	0	0
Warehouse facilities
Other information concerning the credit quality
Totals	1,394	143,200	216,554
Non-Accruing	0	0	0
Commercial non-owner occupied
Other information concerning the credit quality
Totals	522,080	421,583	452,422
Non-Accruing	428	1,164	1,602
Multi-family
Other information concerning the credit quality
Totals	619,485	429,003	397,130
Non-Accruing	0	0	0
One-to-four family
Other information concerning the credit quality
Totals	106,854	80,050	116,735
Non-Accruing	1,340	155	79
Construction
Other information concerning the credit quality
Totals	218,069	169,748	111,704	111,704
Non-Accruing	0	0	0
Land
Other information concerning the credit quality
Totals	18,222	18,340	7,243
Non-Accruing	19	21	0
Other loans
Other information concerning the credit quality
Totals	6,045	5,111	6,641	$ 6,641
Non-Accruing	0	1	0
Current
Other information concerning the credit quality
Current	2,854,329	2,260,051	2,127,575
Current | Commercial and industrial
Other information concerning the credit quality
Current	490,796	309,464	275,850
Current | Franchise
Other information concerning the credit quality
Current	370,245	327,295	214,691
Current | Commercial owner occupied
Other information concerning the credit quality
Current	424,289	294,371	278,953
Current | SBA
Other information concerning the credit quality
Current	78,104	62,256	49,855
Current | Warehouse facilities
Other information concerning the credit quality
Current	1,394	143,200	216,554
Current | Commercial non-owner occupied
Other information concerning the credit quality
Current	522,080	421,369	452,422
Current | Multi-family
Other information concerning the credit quality
Current	619,485	429,003	397,130
Current | One-to-four family
Other information concerning the credit quality
Current	105,619	79,915	116,533
Current | Construction
Other information concerning the credit quality
Current	218,069	169,748	111,704
Current | Land
Other information concerning the credit quality
Current	18,203	18,319	7,243
Current | Other loans
Other information concerning the credit quality
Current	6,045	5,111	6,640
30-59
Other information concerning the credit quality
Days Past Due	247	323	645
30-59 | Commercial and industrial
Other information concerning the credit quality
Days Past Due	0	20	146
30-59 | Franchise
Other information concerning the credit quality
Days Past Due	0	0	0
30-59 | Commercial owner occupied
Other information concerning the credit quality
Days Past Due	0	0	349
30-59 | SBA
Other information concerning the credit quality
Days Past Due	246	0	0
30-59 | Warehouse facilities
Other information concerning the credit quality
Days Past Due	0	0	0
30-59 | Commercial non-owner occupied
Other information concerning the credit quality
Days Past Due	0	214	0
30-59 | Multi-family
Other information concerning the credit quality
Days Past Due	0	0	0
30-59 | One-to-four family
Other information concerning the credit quality
Days Past Due	1	89	149
30-59 | Construction
Other information concerning the credit quality
Days Past Due	0	0	0
30-59 | Land
Other information concerning the credit quality
Days Past Due	0	0	0
30-59 | Other loans
Other information concerning the credit quality
Days Past Due	0	0	1
60-89
Other information concerning the credit quality
Days Past Due	0	355	375
60-89 | Commercial and industrial
Other information concerning the credit quality
Days Past Due	0	0	0
60-89 | Franchise
Other information concerning the credit quality
Days Past Due	0	0	0
60-89 | Commercial owner occupied
Other information concerning the credit quality
Days Past Due	0	355	375
60-89 | SBA
Other information concerning the credit quality
Days Past Due	0	0	0
60-89 | Warehouse facilities
Other information concerning the credit quality
Days Past Due	0	0	0
60-89 | Commercial non-owner occupied
Other information concerning the credit quality
Days Past Due	0	0	0
60-89 | Multi-family
Other information concerning the credit quality
Days Past Due	0	0	0
60-89 | One-to-four family
Other information concerning the credit quality
Days Past Due	0	0	0
60-89 | Construction
Other information concerning the credit quality
Days Past Due	0	0	0
60-89 | Land
Other information concerning the credit quality
Days Past Due	0	0	0
60-89 | Other loans
Other information concerning the credit quality
Days Past Due	0	0	0
90
Other information concerning the credit quality
Days Past Due	3,199	1,954	2,258
90 | Commercial and industrial
Other information concerning the credit quality
Days Past Due	316	257	325
90 | Franchise
Other information concerning the credit quality
Days Past Due	1,630	1,630	1,853
90 | Commercial owner occupied
Other information concerning the credit quality
Days Past Due	0	0	27
90 | SBA
Other information concerning the credit quality
Days Past Due	0	0	0
90 | Warehouse facilities
Other information concerning the credit quality
Days Past Due	0	0	0
90 | Commercial non-owner occupied
Other information concerning the credit quality
Days Past Due	0	0	0
90 | Multi-family
Other information concerning the credit quality
Days Past Due	0	0	0
90 | One-to-four family
Other information concerning the credit quality
Days Past Due	1,234	46	53
90 | Construction
Other information concerning the credit quality
Days Past Due	0	0	0
90 | Land
Other information concerning the credit quality
Days Past Due	19	21	0
90 | Other loans
Other information concerning the credit quality
Days Past Due	$ 0	$ 0	$ 0