Loans Held for Investment - Delinquencies (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Other information concerning the credit quality
Gross loans	$ 4,864,883	$ 3,245,694	$ 2,927,554
Non-Accruing	395	1,141
Commercial and industrial
Other information concerning the credit quality
Gross loans	733,852	563,169	508,141
Non-Accruing	0	250
Franchise
Other information concerning the credit quality
Gross loans	565,415	459,421	403,855
Non-Accruing	0	0
Commercial owner occupied
Other information concerning the credit quality
Gross loans	729,476	454,918	443,060
Non-Accruing	206	436
SBA
Other information concerning the credit quality
Gross loans	108,224	96,705	86,076
Non-Accruing	73	316
Commercial non-owner occupied
Other information concerning the credit quality
Gross loans	1,095,184	586,975	526,362
Non-Accruing	0	0
Multi-family
Other information concerning the credit quality
Gross loans	746,547	690,955	613,573
Non-Accruing	0	0
One-to-four family
Other information concerning the credit quality
Gross loans	322,048	100,451	106,538
Non-Accruing	104	124
Construction
Other information concerning the credit quality
Gross loans	465,295	269,159	215,786
Non-Accruing	12	0
Land
Other information concerning the credit quality
Gross loans	31,799	19,829	18,341
Non-Accruing	12	15
Other loans
Other information concerning the credit quality
Gross loans	7,309	4,112	$ 5,822
Non-Accruing	0	0
Current
Other information concerning the credit quality
Current	4,861,864	3,244,862
Current | Commercial and industrial
Other information concerning the credit quality
Current	733,250	562,805
Current | Franchise
Other information concerning the credit quality
Current	565,415	459,421
Current | Commercial owner occupied
Other information concerning the credit quality
Current	728,403	454,918
Current | SBA
Other information concerning the credit quality
Current	108,057	96,389
Current | Commercial non-owner occupied
Other information concerning the credit quality
Current	1,094,655	586,975
Current | Multi-family
Other information concerning the credit quality
Current	746,310	690,955
Current | One-to-four family
Other information concerning the credit quality
Current	321,653	100,314
Current | Construction
Other information concerning the credit quality
Current	465,279	269,159
Current | Land
Other information concerning the credit quality
Current	31,772	19,814
Current | Other loans
Other information concerning the credit quality
Current	7,226	4,112
30-59
Other information concerning the credit quality
Days Past Due	600	122
30-59 | Commercial and industrial
Other information concerning the credit quality
Days Past Due	225	104
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	17	0
30-59 | Commercial non-owner occupied
Other information concerning the credit quality
Days Past Due	0	0
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	354	18
30-59 | Construction
Other information concerning the credit quality
Days Past Due	4	0
30-59 | Land
Other information concerning the credit quality
Days Past Due	15	0
30-59 | Other loans
Other information concerning the credit quality
Days Past Due	83	0
60-89
Other information concerning the credit quality
Days Past Due	1,965	71
60-89 | Commercial and industrial
Other information concerning the credit quality
Days Past Due	280	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	901	0
60-89 | SBA
Other information concerning the credit quality
Days Past Due	18	0
60-89 | Commercial non-owner occupied
Other information concerning the credit quality
Days Past Due	529	0
60-89 | Multi-family
Other information concerning the credit quality
Days Past Due	237	0
60-89 | One-to-four family
Other information concerning the credit quality
Days Past Due	0	71
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	454	639
90 | Commercial and industrial
Other information concerning the credit quality
Days Past Due	97	260
90 | Franchise
Other information concerning the credit quality
Days Past Due	0	0
90 | Commercial owner occupied
Other information concerning the credit quality
Days Past Due	172	0
90 | SBA
Other information concerning the credit quality
Days Past Due	132	316
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	41	48
90 | Construction
Other information concerning the credit quality
Days Past Due	12	0
90 | Land
Other information concerning the credit quality
Days Past Due	12	15
90 | Other loans
Other information concerning the credit quality
Days Past Due	$ 0	$ 0