Loans - Days past due and Non-accruing (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Other information concerning the credit quality
Total Gross Loans	$ 8,852,005	$ 6,222,053
Non-accruing	4,857	3,284
Warehouse Facilities
Other information concerning the credit quality
Total Gross Loans		116,066
Current
Other information concerning the credit quality
Current	8,839,152	6,211,994
30-59
Other information concerning the credit quality
Days Past Due	7,046	5,964
60-89
Other information concerning the credit quality
Days Past Due	1,242	1,056
90
Other information concerning the credit quality
Days Past Due	4,565	3,039
Business Loans | Commercial and industrial
Other information concerning the credit quality
Total Gross Loans	1,364,461	1,086,659
Non-accruing	931	1,160
Business Loans | Franchise
Other information concerning the credit quality
Total Gross Loans	765,416	660,415
Non-accruing	190	0
Business Loans | Commercial owner occupied
Other information concerning the credit quality
Total Gross Loans	1,679,122	1,295,214
Non-accruing	599	97
Business Loans | SBA
Other information concerning the credit quality
Total Gross Loans	198,201	202,938
Non-accruing	2,739	1,201
Business Loans | Warehouse Facilities
Other information concerning the credit quality
Total Gross Loans		116,066
Non-accruing		0
Business Loans | Agribusiness
Other information concerning the credit quality
Total Gross Loans	138,519
Non-accruing	0
Business Loans | Current | Commercial and industrial
Other information concerning the credit quality
Current	1,362,017	1,085,770
Business Loans | Current | Franchise
Other information concerning the credit quality
Current	759,546	660,415
Business Loans | Current | Commercial owner occupied
Other information concerning the credit quality
Current	1,677,967	1,291,254
Business Loans | Current | SBA
Other information concerning the credit quality
Current	195,051	200,821
Business Loans | Current | Warehouse Facilities
Other information concerning the credit quality
Current		116,066
Business Loans | Current | Agribusiness
Other information concerning the credit quality
Current	138,519
Business Loans | 30-59 | Commercial and industrial
Other information concerning the credit quality
Days Past Due	309	84
Business Loans | 30-59 | Franchise
Other information concerning the credit quality
Days Past Due	5,680	0
Business Loans | 30-59 | Commercial owner occupied
Other information concerning the credit quality
Days Past Due	343	3,474
Business Loans | 30-59 | SBA
Other information concerning the credit quality
Days Past Due	524	177
Business Loans | 30-59 | Warehouse Facilities
Other information concerning the credit quality
Days Past Due		0
Business Loans | 30-59 | Agribusiness
Other information concerning the credit quality
Days Past Due	0
Business Loans | 60-89 | Commercial and industrial
Other information concerning the credit quality
Days Past Due	1,204	570
Business Loans | 60-89 | Franchise
Other information concerning the credit quality
Days Past Due	0	0
Business Loans | 60-89 | Commercial owner occupied
Other information concerning the credit quality
Days Past Due	0	486
Business Loans | 60-89 | SBA
Other information concerning the credit quality
Days Past Due	0	0
Business Loans | 60-89 | Warehouse Facilities
Other information concerning the credit quality
Days Past Due		0
Business Loans | 60-89 | Agribusiness
Other information concerning the credit quality
Days Past Due	0
Business Loans | 90 | Commercial and industrial
Other information concerning the credit quality
Days Past Due	931	235
Business Loans | 90 | Franchise
Other information concerning the credit quality
Days Past Due	190	0
Business Loans | 90 | Commercial owner occupied
Other information concerning the credit quality
Days Past Due	812	0
Business Loans | 90 | SBA
Other information concerning the credit quality
Days Past Due	2,626	1,940
Business Loans | 90 | Warehouse Facilities
Other information concerning the credit quality
Days Past Due		0
Business Loans | 90 | Agribusiness
Other information concerning the credit quality
Days Past Due	0
Real Estate Loans | Commercial non-owner occupied
Other information concerning the credit quality
Total Gross Loans	2,004,536	1,243,115
Non-accruing	0	0
Real Estate Loans | Multi-family
Other information concerning the credit quality
Total Gross Loans	1,535,289	794,384
Non-accruing	0	0
Real Estate Loans | One-to-four family
Other information concerning the credit quality
Total Gross Loans	356,264	270,894
Non-accruing	398	817
Real Estate Loans | Construction
Other information concerning the credit quality
Total Gross Loans	523,643	282,811
Non-accruing	0	0
Real Estate Loans | Farmland
Other information concerning the credit quality
Total Gross Loans	150,502	145,393
Non-accruing	0	0
Real Estate Loans | Land
Other information concerning the credit quality
Total Gross Loans	46,628	31,233
Non-accruing	0	9
Real Estate Loans | Current | Commercial non-owner occupied
Other information concerning the credit quality
Current	2,004,536	1,243,115
Real Estate Loans | Current | Multi-family
Other information concerning the credit quality
Current	1,535,275	792,603
Real Estate Loans | Current | One-to-four family
Other information concerning the credit quality
Current	356,219	269,725
Real Estate Loans | Current | Construction
Other information concerning the credit quality
Current	523,643	282,811
Real Estate Loans | Current | Farmland
Other information concerning the credit quality
Current	150,502	145,393
Real Estate Loans | Current | Land
Other information concerning the credit quality
Current	46,628	31,141
Real Estate Loans | 30-59 | Commercial non-owner occupied
Other information concerning the credit quality
Days Past Due	0	0
Real Estate Loans | 30-59 | Multi-family
Other information concerning the credit quality
Days Past Due	14	1,781
Real Estate Loans | 30-59 | One-to-four family
Other information concerning the credit quality
Days Past Due	30	354
Real Estate Loans | 30-59 | Construction
Other information concerning the credit quality
Days Past Due	0	0
Real Estate Loans | 30-59 | Farmland
Other information concerning the credit quality
Days Past Due	0	0
Real Estate Loans | 30-59 | Land
Other information concerning the credit quality
Days Past Due	0	83
Real Estate Loans | 60-89 | Commercial non-owner occupied
Other information concerning the credit quality
Days Past Due	0	0
Real Estate Loans | 60-89 | Multi-family
Other information concerning the credit quality
Days Past Due	0	0
Real Estate Loans | 60-89 | One-to-four family
Other information concerning the credit quality
Days Past Due	9	0
Real Estate Loans | 60-89 | Construction
Other information concerning the credit quality
Days Past Due	0	0
Real Estate Loans | 60-89 | Farmland
Other information concerning the credit quality
Days Past Due	0	0
Real Estate Loans | 60-89 | Land
Other information concerning the credit quality
Days Past Due	0	0
Real Estate Loans | 90 | Commercial non-owner occupied
Other information concerning the credit quality
Days Past Due	0	0
Real Estate Loans | 90 | Multi-family
Other information concerning the credit quality
Days Past Due	0	0
Real Estate Loans | 90 | One-to-four family
Other information concerning the credit quality
Days Past Due	6	815
Real Estate Loans | 90 | Construction
Other information concerning the credit quality
Days Past Due	0	0
Real Estate Loans | 90 | Farmland
Other information concerning the credit quality
Days Past Due	0	0
Real Estate Loans | 90 | Land
Other information concerning the credit quality
Days Past Due	0	9
Consumer Loans | Consumer loans
Other information concerning the credit quality
Total Gross Loans	89,424	92,931
Non-accruing	0	0
Consumer Loans | Current | Consumer loans
Other information concerning the credit quality
Current	89,249	92,880
Consumer Loans | 30-59 | Consumer loans
Other information concerning the credit quality
Days Past Due	146	11
Consumer Loans | 60-89 | Consumer loans
Other information concerning the credit quality
Days Past Due	29	0
Consumer Loans | 90 | Consumer loans
Other information concerning the credit quality
Days Past Due	$ 0	$ 40