Allowance for loan losses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 3,562	$ 5,729	$ 7,239
Provision for (Recovery of) Loan Losses	0	(2,000)	100
Charge-offs	(544)	(816)	(2,381)
Recoveries	355	649	771
Ending balance	3,373	3,562	5,729
Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	30	34	135
Provision for (Recovery of) Loan Losses	10	(6)	(103)
Charge-offs	0	0	0
Recoveries	1	2	2
Ending balance	41	30	34
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	291	202	1,274
Provision for (Recovery of) Loan Losses	9	292	(1,016)
Charge-offs	(10)	(252)	(100)
Recoveries	10	49	44
Ending balance	300	291	202
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,695	2,651	2,226
Provision for (Recovery of) Loan Losses	(730)	(866)	1,645
Charge-offs	(67)	(127)	(1,245)
Recoveries	178	37	25
Ending balance	1,076	1,695	2,651
Home equity lines [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	448	469	424
Provision for (Recovery of) Loan Losses	(127)	36	506
Charge-offs	(53)	(62)	(476)
Recoveries	3	5	15
Ending balance	271	448	469
Construction and Land Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	321	236	1,409
Provision for (Recovery of) Loan Losses	19	286	(1,119)
Charge-offs	(10)	(252)	(100)
Recoveries	11	51	46
Ending balance	341	321	236
Owner Occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,167	1,837	1,200
Provision for (Recovery of) Loan Losses	(490)	(576)	1,268
Charge-offs	(66)	(127)	(631)
Recoveries	0	33	0
Ending balance	611	1,167	1,837
Non-Owner Occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	460	607	670
Provision for (Recovery of) Loan Losses	(106)	(151)	430
Charge-offs	(1)	0	(518)
Recoveries	53	4	25
Ending balance	406	460	607
Multifamily [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	51	77	19
Provision for (Recovery of) Loan Losses	5	(26)	58
Charge-offs	0	0	0
Recoveries	0	0	0
Ending balance	56	51	77
Farmland [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	17	130	337
Provision for (Recovery of) Loan Losses	(139)	(113)	(111)
Charge-offs	0	0	(96)
Recoveries	125	0	0
Ending balance	3	17	130
First Deed of Trust [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	602	1,345	1,992
Provision for (Recovery of) Loan Losses	(40)	(1,020)	(442)
Charge-offs	(140)	(103)	(277)
Recoveries	25	380	72
Ending balance	447	602	1,345
Second Deed of Trust [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	111	275	394
Provision for (Recovery of) Loan Losses	21	(159)	(223)
Charge-offs	(25)	(55)	(86)
Recoveries	29	50	190
Ending balance	136	111	275
Consumer Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,161	2,089	2,810
Provision for (Recovery of) Loan Losses	(146)	(1,143)	(159)
Charge-offs	(218)	(220)	(839)
Recoveries	57	435	277
Ending balance	854	1,161	2,089
Commercial and industrial loans (except those secured by real estate) [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	94	506	724
Provision for (Recovery of) Loan Losses	44	(350)	(447)
Charge-offs	(15)	(162)	(172)
Recoveries	100	100	401
Ending balance	223	94	506
Guaranteed student loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	230	217	0
Provision for (Recovery of) Loan Losses	149	13	217
Charge-offs	(221)	0	0
Recoveries	0	0	0
Ending balance	158	230	217
Consumer And Other [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	2	30	70
Provision for (Recovery of) Loan Losses	10	1	(37)
Charge-offs	(13)	(55)	(25)
Recoveries	9	26	22
Ending balance	8	2	30
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	59	0
Provision for (Recovery of) Loan Losses	654	59
Charge-offs	0	0
Recoveries	0	0
Ending balance	$ 713	$ 59	$ 0