- Internal risk grading system (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) area grade	Dec. 31, 2015 USD ($)
Receivables [Abstract]
Number of areas where the entity's credit quality is maintained and credit risk managed | area	2
Number of Pass scale grades | grade	6
Credit Risk Grades
Total Gross Loans	$ 3,245,694	$ 2,262,683
Business loans: Commercial and industrial
Credit Risk Grades
Total Gross Loans	563,169	309,741
Business loans: Franchise loans
Credit Risk Grades
Total Gross Loans	459,421	328,925
Business loans: Commercial owner occupied
Credit Risk Grades
Total Gross Loans	454,918	294,726
Business loans: SBA
Credit Risk Grades
Total Gross Loans	96,705	62,256
Business loans: Warehouse facilities
Credit Risk Grades
Total Gross Loans		143,200
Real estate loans: Commercial non-owner occupied
Credit Risk Grades
Total Gross Loans	586,975	421,583
Real estate loans: Multi-family
Credit Risk Grades
Total Gross Loans	690,955	429,003
Real estate loans: One-to-four family
Credit Risk Grades
Total Gross Loans	100,451	80,050
Real estate loans: Construction
Credit Risk Grades
Total Gross Loans	269,159	169,748
Real estate loans: Land
Credit Risk Grades
Total Gross Loans	19,829	18,340
Other loans
Credit Risk Grades
Total Gross Loans	4,112	5,111
Pass
Credit Risk Grades
Total Gross Loans	3,216,683	2,242,242
Pass | Business loans: Commercial and industrial
Credit Risk Grades
Total Gross Loans	550,919	306,513
Pass | Business loans: Franchise loans
Credit Risk Grades
Total Gross Loans	459,421	327,295
Pass | Business loans: Commercial owner occupied
Credit Risk Grades
Total Gross Loans	450,416	286,270
Pass | Business loans: SBA
Credit Risk Grades
Total Gross Loans	96,190	62,256
Pass | Business loans: Warehouse facilities
Credit Risk Grades
Total Gross Loans		143,200
Pass | Real estate loans: Commercial non-owner occupied
Credit Risk Grades
Total Gross Loans	585,093	418,917
Pass | Real estate loans: Multi-family
Credit Risk Grades
Total Gross Loans	681,942	425,616
Pass | Real estate loans: One-to-four family
Credit Risk Grades
Total Gross Loans	100,010	78,997
Pass | Real estate loans: Construction
Credit Risk Grades
Total Gross Loans	269,159	169,748
Pass | Real estate loans: Land
Credit Risk Grades
Total Gross Loans	19,814	18,319
Pass | Other loans
Credit Risk Grades
Total Gross Loans	3,719	5,111
Special Mention
Credit Risk Grades
Total Gross Loans	15,970	700
Special Mention | Business loans: Commercial and industrial
Credit Risk Grades
Total Gross Loans	8,216	73
Special Mention | Business loans: Franchise loans
Credit Risk Grades
Total Gross Loans	0	0
Special Mention | Business loans: Commercial owner occupied
Credit Risk Grades
Total Gross Loans	281	627
Special Mention | Business loans: SBA
Credit Risk Grades
Total Gross Loans	53	0
Special Mention | Business loans: Warehouse facilities
Credit Risk Grades
Total Gross Loans		0
Special Mention | Real estate loans: Commercial non-owner occupied
Credit Risk Grades
Total Gross Loans	810	0
Special Mention | Real estate loans: Multi-family
Credit Risk Grades
Total Gross Loans	6,610	0
Special Mention | Real estate loans: One-to-four family
Credit Risk Grades
Total Gross Loans	0	0
Special Mention | Real estate loans: Construction
Credit Risk Grades
Total Gross Loans	0	0
Special Mention | Real estate loans: Land
Credit Risk Grades
Total Gross Loans	0	0
Special Mention | Other loans
Credit Risk Grades
Total Gross Loans	0	0
Substandard
Credit Risk Grades
Total Gross Loans	12,791	18,280
Substandard | Business loans: Commercial and industrial
Credit Risk Grades
Total Gross Loans	3,784	3,155
Substandard | Business loans: Franchise loans
Credit Risk Grades
Total Gross Loans	0	169
Substandard | Business loans: Commercial owner occupied
Credit Risk Grades
Total Gross Loans	4,221	7,829
Substandard | Business loans: SBA
Credit Risk Grades
Total Gross Loans	462	0
Substandard | Business loans: Warehouse facilities
Credit Risk Grades
Total Gross Loans		0
Substandard | Real estate loans: Commercial non-owner occupied
Credit Risk Grades
Total Gross Loans	1,072	2,666
Substandard | Real estate loans: Multi-family
Credit Risk Grades
Total Gross Loans	2,403	3,387
Substandard | Real estate loans: One-to-four family
Credit Risk Grades
Total Gross Loans	441	1,053
Substandard | Real estate loans: Construction
Credit Risk Grades
Total Gross Loans	0	0
Substandard | Real estate loans: Land
Credit Risk Grades
Total Gross Loans	15	21
Substandard | Other loans
Credit Risk Grades
Total Gross Loans	393	0
Doubtful
Credit Risk Grades
Total Gross Loans	250	1,461
Doubtful | Business loans: Commercial and industrial
Credit Risk Grades
Total Gross Loans	250	0
Doubtful | Business loans: Franchise loans
Credit Risk Grades
Total Gross Loans	0	1,461
Doubtful | Business loans: Commercial owner occupied
Credit Risk Grades
Total Gross Loans	0	0
Doubtful | Business loans: SBA
Credit Risk Grades
Total Gross Loans	0	0
Doubtful | Business loans: Warehouse facilities
Credit Risk Grades
Total Gross Loans		0
Doubtful | Real estate loans: Commercial non-owner occupied
Credit Risk Grades
Total Gross Loans	0	0
Doubtful | Real estate loans: Multi-family
Credit Risk Grades
Total Gross Loans	0	0
Doubtful | Real estate loans: One-to-four family
Credit Risk Grades
Total Gross Loans	0	0
Doubtful | Real estate loans: Construction
Credit Risk Grades
Total Gross Loans	0	0
Doubtful | Real estate loans: Land
Credit Risk Grades
Total Gross Loans	0	0
Doubtful | Other loans
Credit Risk Grades
Total Gross Loans	$ 0	$ 0