Internal risk grading system (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) area grade	Dec. 31, 2014 USD ($)	Dec. 31, 2013 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	$ 2,262,683	$ 1,628,445	$ 1,243,252
Business loans: Commercial and industrial
Credit Risk Grades
Total Gross Loans	309,741	228,979	187,035
Business loans: Franchise loans
Credit Risk Grades
Total Gross Loans	328,925	199,228	0
Business loans: Commercial owner occupied
Credit Risk Grades
Total Gross Loans	294,726	210,995	221,089
Business loans: SBA
Credit Risk Grades
Total Gross Loans	62,256	28,404	10,659
Business loans: Warehouse facilities
Credit Risk Grades
Total Gross Loans	143,200	113,798	87,517
Real estate loans: Commercial non-owner occupied
Credit Risk Grades
Total Gross Loans	421,583	359,213	333,544
Real estate loans: Multi-family
Credit Risk Grades
Total Gross Loans	429,003	262,965	233,689
Real estate loans: One-to-four family
Credit Risk Grades
Total Gross Loans	80,050	122,795	145,235
Real estate loans: Construction
Credit Risk Grades
Total Gross Loans	169,748	89,682	13,040
Real estate loans: Land
Credit Risk Grades
Total Gross Loans	18,340	9,088	7,605
Other loans
Credit Risk Grades
Total Gross Loans	5,111	3,298	$ 3,839
Pass
Credit Risk Grades
Total Gross Loans	2,242,242	1,612,143
Pass | Business loans: Commercial and industrial
Credit Risk Grades
Total Gross Loans	306,513	227,151
Pass | Business loans: Franchise loans
Credit Risk Grades
Total Gross Loans	327,295	199,228
Pass | Business loans: Commercial owner occupied
Credit Risk Grades
Total Gross Loans	286,270	202,390
Pass | Business loans: SBA
Credit Risk Grades
Total Gross Loans	62,256	28,132
Pass | Business loans: Warehouse facilities
Credit Risk Grades
Total Gross Loans	143,200	113,798
Pass | Real estate loans: Commercial non-owner occupied
Credit Risk Grades
Total Gross Loans	418,917	355,274
Pass | Real estate loans: Multi-family
Credit Risk Grades
Total Gross Loans	425,616	261,956
Pass | Real estate loans: One-to-four family
Credit Risk Grades
Total Gross Loans	78,997	122,146
Pass | Real estate loans: Construction
Credit Risk Grades
Total Gross Loans	169,748	89,682
Pass | Real estate loans: Land
Credit Risk Grades
Total Gross Loans	18,319	9,088
Pass | Other loans
Credit Risk Grades
Total Gross Loans	5,111	3,298
Special Mention
Credit Risk Grades
Total Gross Loans	700	773
Special Mention | Business loans: Commercial and industrial
Credit Risk Grades
Total Gross Loans	73	0
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	627	0
Special Mention | Business loans: SBA
Credit Risk Grades
Total Gross Loans	0	272
Special Mention | Business loans: Warehouse facilities
Credit Risk Grades
Total Gross Loans	0	0
Special Mention | Real estate loans: Commercial non-owner occupied
Credit Risk Grades
Total Gross Loans	0	0
Special Mention | Real estate loans: Multi-family
Credit Risk Grades
Total Gross Loans	0	501
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	18,280	15,529
Substandard | Business loans: Commercial and industrial
Credit Risk Grades
Total Gross Loans	3,155	1,828
Substandard | Business loans: Franchise loans
Credit Risk Grades
Total Gross Loans	169	0
Substandard | Business loans: Commercial owner occupied
Credit Risk Grades
Total Gross Loans	7,829	8,605
Substandard | Business loans: SBA
Credit Risk Grades
Total Gross Loans	0	0
Substandard | Business loans: Warehouse facilities
Credit Risk Grades
Total Gross Loans	0	0
Substandard | Real estate loans: Commercial non-owner occupied
Credit Risk Grades
Total Gross Loans	2,666	3,939
Substandard | Real estate loans: Multi-family
Credit Risk Grades
Total Gross Loans	3,387	508
Substandard | Real estate loans: One-to-four family
Credit Risk Grades
Total Gross Loans	1,053	649
Substandard | Real estate loans: Construction
Credit Risk Grades
Total Gross Loans	0	0
Substandard | Real estate loans: Land
Credit Risk Grades
Total Gross Loans	21	0
Substandard | Other loans
Credit Risk Grades
Total Gross Loans	0	0
Doubtful
Credit Risk Grades
Total Gross Loans	1,461	0
Doubtful | Business loans: Commercial and industrial
Credit Risk Grades
Total Gross Loans	0	0
Doubtful | Business loans: Franchise loans
Credit Risk Grades
Total Gross Loans	1,461	0
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	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