Loans and Allowance for Loan and Lease Losses - Schedule of composition of loan portfolio (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable
Gross loans	$ 1,278,981		$ 1,126,339
Deferred fee (income) costs, net	1,871		4,783
Allowance for loan and lease losses	(17,485)	$ (18,166)	(13,611)	$ (12,086)	$ (11,474)	$ (13,506)
Loans, net	$ 1,263,367		$ 1,117,511
Percentage of loan portfolio	100.00%		100.00%
Commercial loans
Accounts, Notes, Loans and Financing Receivable
Gross loans	$ 614,737		$ 409,420
Allowance for loan and lease losses	$ (10,932)	(11,487)	$ (8,883)	(7,520)	(6,809)	(8,071)
Percentage of loan portfolio	48.10%		36.20%
Commercial real estate loans – owner occupied
Accounts, Notes, Loans and Financing Receivable
Gross loans	$ 195,586		$ 219,483
Percentage of loan portfolio	15.30%		19.50%
Commercial real estate loans – all other
Accounts, Notes, Loans and Financing Receivable
Gross loans	$ 199,911		$ 208,283
Percentage of loan portfolio	15.60%		18.50%
Residential mortgage loans – multi-family
Accounts, Notes, Loans and Financing Receivable
Gross loans	$ 161,947		$ 176,523
Percentage of loan portfolio	12.70%		15.70%
Residential mortgage loans – single family
Accounts, Notes, Loans and Financing Receivable
Gross loans	$ 13,764		$ 18,782
Percentage of loan portfolio	1.10%		1.70%
Construction and land development loans
Accounts, Notes, Loans and Financing Receivable
Gross loans	$ 9,300		$ 2,981
Allowance for loan and lease losses	$ (114)	$ (77)	$ (34)	$ (83)	$ (119)	$ (426)
Percentage of loan portfolio	0.70%		0.30%
Consumer loans
Accounts, Notes, Loans and Financing Receivable
Gross loans	$ 83,736		$ 90,867
Percentage of loan portfolio	6.50%		8.10%