Loans Held for Investment - Internal Risk Grading System (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Credit Risk Grades
Totals	$ 3,095,540	$ 2,262,683	$ 2,167,547
Commercial and industrial
Credit Risk Grades
Totals	537,809	309,741	288,982
Franchise
Credit Risk Grades
Totals	431,618	328,925	295,965
Commercial owner occupied
Credit Risk Grades
Totals	460,068	294,726	302,556
SBA
Credit Risk Grades
Totals	92,195	62,256	70,191
Warehouse facilities
Credit Risk Grades
Totals	0	143,200	144,274
Commercial non-owner occupied
Credit Risk Grades
Totals	527,412	421,583	406,490
Multi-family
Credit Risk Grades
Totals	689,813	429,003	421,240
One-to-four family
Credit Risk Grades
Totals	101,377	80,050	78,781
Construction
Credit Risk Grades
Totals	231,098	169,748	141,293
Land
Credit Risk Grades
Totals	18,472	18,340	12,758
Other loans
Credit Risk Grades
Totals	5,678	5,111	$ 5,017
Pass
Credit Risk Grades
Totals	3,067,596	2,242,242
Pass | Commercial and industrial
Credit Risk Grades
Totals	525,979	306,513
Pass | Franchise
Credit Risk Grades
Totals	430,934	327,295
Pass | Commercial owner occupied
Credit Risk Grades
Totals	452,461	286,270
Pass | SBA
Credit Risk Grades
Totals	91,692	62,256
Pass | Warehouse facilities
Credit Risk Grades
Totals		143,200
Pass | Commercial non-owner occupied
Credit Risk Grades
Totals	523,837	418,917
Pass | Multi-family
Credit Risk Grades
Totals	687,396	425,616
Pass | One-to-four family
Credit Risk Grades
Totals	100,488	78,997
Pass | Construction
Credit Risk Grades
Totals	231,098	169,748
Pass | Land
Credit Risk Grades
Totals	18,455	18,319
Pass | Other loans
Credit Risk Grades
Totals	5,256	5,111
Special Mention
Credit Risk Grades
Totals	6,737	700
Special Mention | Commercial and industrial
Credit Risk Grades
Totals	4,034	73
Special Mention | Franchise
Credit Risk Grades
Totals	684	0
Special Mention | Commercial owner occupied
Credit Risk Grades
Totals	2,019	627
Special Mention | SBA
Credit Risk Grades
Totals	0	0
Special Mention | Warehouse facilities
Credit Risk Grades
Totals		0
Special Mention | Commercial non-owner occupied
Credit Risk Grades
Totals	0	0
Special Mention | Multi-family
Credit Risk Grades
Totals	0	0
Special Mention | One-to-four family
Credit Risk Grades
Totals	0	0
Special Mention | Construction
Credit Risk Grades
Totals	0	0
Special Mention | Land
Credit Risk Grades
Totals	0	0
Special Mention | Other loans
Credit Risk Grades
Totals	0	0
Substandard
Credit Risk Grades
Totals	19,217	18,280
Substandard | Commercial and industrial
Credit Risk Grades
Totals	5,806	3,155
Substandard | Franchise
Credit Risk Grades
Totals	0	169
Substandard | Commercial owner occupied
Credit Risk Grades
Totals	5,588	7,829
Substandard | SBA
Credit Risk Grades
Totals	503	0
Substandard | Warehouse facilities
Credit Risk Grades
Totals		0
Substandard | Commercial non-owner occupied
Credit Risk Grades
Totals	3,575	2,666
Substandard | Multi-family
Credit Risk Grades
Totals	2,417	3,387
Substandard | One-to-four family
Credit Risk Grades
Totals	889	1,053
Substandard | Construction
Credit Risk Grades
Totals	0	0
Substandard | Land
Credit Risk Grades
Totals	17	21
Substandard | Other loans
Credit Risk Grades
Totals	422	0
Doubtful
Credit Risk Grades
Totals	1,990	1,461
Doubtful | Commercial and industrial
Credit Risk Grades
Totals	1,990	0
Doubtful | Franchise
Credit Risk Grades
Totals	0	1,461
Doubtful | Commercial owner occupied
Credit Risk Grades
Totals	0	0
Doubtful | SBA
Credit Risk Grades
Totals	0	0
Doubtful | Warehouse facilities
Credit Risk Grades
Totals		0
Doubtful | Commercial non-owner occupied
Credit Risk Grades
Totals	0	0
Doubtful | Multi-family
Credit Risk Grades
Totals	0	0
Doubtful | One-to-four family
Credit Risk Grades
Totals	0	0
Doubtful | Construction
Credit Risk Grades
Totals	0	0
Doubtful | Land
Credit Risk Grades
Totals	0	0
Doubtful | Other loans
Credit Risk Grades
Totals	$ 0	$ 0