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Loans and allowance for loan losses (Schedule of summary loan portfolio) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Loans and Leases Receivable Disclosure [Line Items]
Total gross loans	$ 757,098		$ 677,006	$ 651,046
Net deferred loan costs	9,804		8,042
Allowance for loan losses	(7,903)	$ (7,858)	(6,646)	(6,310)	$ (5,939)	$ (5,457)
Total net loans	758,999		678,402
Indirect
Loans and Leases Receivable Disclosure [Line Items]
Total gross loans	354,394		297,144	272,892
Allowance for loan losses	(4,183)	(3,606)	(2,915)	(3,195)	(2,621)	(2,150)
Commercial real estate
Loans and Leases Receivable Disclosure [Line Items]
Total gross loans	245,704		223,030	224,699
Allowance for loan losses	(1,173)	(1,252)	(1,080)	(870)	(947)	(1,305)
Commercial real estate \| Undisbursed construction loans
Loans and Leases Receivable Disclosure [Line Items]
Total gross loans	16,654		12,870
Commercial real estate \| Non-residential
Loans and Leases Receivable Disclosure [Line Items]
Total gross loans	208,778		197,499
Commercial real estate \| Multifamily
Loans and Leases Receivable Disclosure [Line Items]
Total gross loans	20,272		12,661
Residential real estate
Loans and Leases Receivable Disclosure [Line Items]
Total gross loans	41,344		43,534	44,387
Allowance for loan losses	(256)	(305)	(320)	(474)	(513)	(455)
Commercial and industrial
Loans and Leases Receivable Disclosure [Line Items]
Total gross loans	88,187		83,203	79,055
Allowance for loan losses	(1,590)	(1,895)	(1,542)	(1,055)	(1,082)	(879)
Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total gross loans	27,469		30,095	30,013
Allowance for loan losses	(701)	$ (800)	(789)	$ (716)	$ (776)	$ (668)
Consumer \| Indirect
Loans and Leases Receivable Disclosure [Line Items]
Total gross loans	354,394		297,144
Consumer \| Home equity
Loans and Leases Receivable Disclosure [Line Items]
Total gross loans	17,336		19,269
Consumer \| Other consumer
Loans and Leases Receivable Disclosure [Line Items]
Total gross loans	$ 10,133		$ 10,826