Loans and allowance for loan losses (Schedule of loan balances by segment) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Allowance for loan losses:
Beginning balance	$ 7,858	$ 5,939	$ 6,646	$ 5,457	$ 5,457
Provision (credit) for loan losses	450	525	2,010	1,575	2,100
Loans charged-off	(604)	(372)	(1,550)	(1,456)	(2,013)
Recoveries	199	218	797	734	1,102
Ending balance	7,903	6,310	7,903	6,310	6,646
Allowance for loan losses:
Ending balance: Loans deemed impaired	124	99	124	99	50
Ending balance: Loans not deemed impaired	7,779	6,211	7,779	6,211	6,596
Loan receivables:
Ending balance	757,098	651,046	757,098	651,046	677,006
Ending balance: Loans deemed impaired	8,773	8,579	8,773	8,579	5,749
Ending balance: Loans not deemed impaired	748,325	642,467	748,325	642,467	671,257
Indirect
Allowance for loan losses:
Beginning balance	3,606	2,621	2,915	2,150	2,150
Provision (credit) for loan losses	898	728	1,930	1,545	1,539
Loans charged-off	(494)	(365)	(1,413)	(1,100)	(1,607)
Recoveries	173	211	751	600	833
Ending balance	4,183	3,195	4,183	3,195	2,915
Allowance for loan losses:
Ending balance: Loans deemed impaired	118	83	118	83	50
Ending balance: Loans not deemed impaired	4,065	3,112	4,065	3,112	2,865
Loan receivables:
Ending balance	354,394	272,892	354,394	272,892	297,144
Ending balance: Loans deemed impaired	673	542	673	542	452
Ending balance: Loans not deemed impaired	353,721	272,350	353,721	272,350	296,692
Commercial real estate
Allowance for loan losses:
Beginning balance	1,252	947	1,080	1,305	1,305
Provision (credit) for loan losses	(79)	(77)	93	(132)	(45)
Loans charged-off	0	0	0	(303)	(303)
Recoveries	0	0	0	0	123
Ending balance	1,173	870	1,173	870	1,080
Allowance for loan losses:
Ending balance: Loans deemed impaired	0	0	0	0	0
Ending balance: Loans not deemed impaired	1,173	870	1,173	870	1,080
Loan receivables:
Ending balance	245,704	224,699	245,704	224,699	223,030
Ending balance: Loans deemed impaired	4,238	4,668	4,238	4,668	2,507
Ending balance: Loans not deemed impaired	241,466	220,031	241,466	220,031	220,523
Residential real estate
Allowance for loan losses:
Beginning balance	305	513	320	455	455
Provision (credit) for loan losses	(49)	(40)	(67)	15	(140)
Loans charged-off	0	0	0	0	0
Recoveries	0	1	3	4	5
Ending balance	256	474	256	474	320
Allowance for loan losses:
Ending balance: Loans deemed impaired	0	0	0	0	0
Ending balance: Loans not deemed impaired	256	474	256	474	320
Loan receivables:
Ending balance	41,344	44,387	41,344	44,387	43,534
Ending balance: Loans deemed impaired	2,657	2,445	2,657	2,445	2,285
Ending balance: Loans not deemed impaired	38,687	41,942	38,687	41,942	41,249
Commercial and industrial
Allowance for loan losses:
Beginning balance	1,895	1,082	1,542	879	879
Provision (credit) for loan losses	(276)	(27)	89	91	578
Loans charged-off	(43)	(1)	(55)	(28)	(37)
Recoveries	14	1	14	113	122
Ending balance	1,590	1,055	1,590	1,055	1,542
Allowance for loan losses:
Ending balance: Loans deemed impaired	0	5	0	5	0
Ending balance: Loans not deemed impaired	1,590	1,050	1,590	1,050	1,542
Loan receivables:
Ending balance	88,187	79,055	88,187	79,055	83,203
Ending balance: Loans deemed impaired	674	630	674	630	297
Ending balance: Loans not deemed impaired	87,513	78,425	87,513	78,425	82,906
Consumer
Allowance for loan losses:
Beginning balance	800	776	789	668	668
Provision (credit) for loan losses	(44)	(59)	(35)	56	168
Loans charged-off	(67)	(6)	(82)	(25)	(66)
Recoveries	12	5	29	17	19
Ending balance	701	716	701	716	789
Allowance for loan losses:
Ending balance: Loans deemed impaired	6	11	6	11	0
Ending balance: Loans not deemed impaired	695	705	695	705	789
Loan receivables:
Ending balance	27,469	30,013	27,469	30,013	30,095
Ending balance: Loans deemed impaired	531	294	531	294	208
Ending balance: Loans not deemed impaired	26,938	$ 29,719	26,938	$ 29,719	29,887
Consumer | Indirect
Loan receivables:
Ending balance	$ 354,394		$ 354,394		$ 297,144