Loans and allowance for credit losses - Allowance for credit losses on loans losses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 3,681	$ 3,256	$ 3,423	$ 3,370	$ 3,370
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	3,681	3,256	3,423	3,370	3,370
Provision for (Recovery of) Credit Losses	(9)	(53)	128	(52)	(21)
Charge-offs			(16)	(23)	(33)
Charge-offs	(5)	(16)			(33)
Recoveries	33	166	165	185	192
Ending Balance	3,700	3,353	3,700	3,353	3,423
Adoption of ASC 326
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Impact of adoption ASC 326				(127)	(127)
Construction and land development
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	290	329	314	271	271
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	290	329	314	271	271
Provision for (Recovery of) Credit Losses	24	36		57	(6)
Ending Balance	314	365	314	365	314
Construction and land development | Adoption of ASC 326
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Impact of adoption ASC 326				37	37
Construction and land development | Residential
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	84	61	86	79	79
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	84	61	86	79	79
Provision for (Recovery of) Credit Losses	18	12	16	(9)	(4)
Ending Balance	102	73	102	73	86
Construction and land development | Residential | Adoption of ASC 326
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Impact of adoption ASC 326				3	3
Construction and land development | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	206	268	228	192	192
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	206	268	228	192	192
Provision for (Recovery of) Credit Losses	6	24	(16)	66	(2)
Ending Balance	212	292	212	292	228
Construction and land development | Commercial | Adoption of ASC 326
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Impact of adoption ASC 326				34	34
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	2,015	1,799	1,923	2,189	2,189
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	2,015	1,799	1,923	2,189	2,189
Provision for (Recovery of) Credit Losses	9	80	101	(34)	(10)
Ending Balance	2,024	1,879	2,024	1,879	1,923
Commercial real estate | Adoption of ASC 326
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Impact of adoption ASC 326				(276)	(276)
Commercial real estate | Owner occupied
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	461	379	409	867	867
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	461	379	409	867	867
Provision for (Recovery of) Credit Losses	5	18	57	5	(17)
Ending Balance	466	397	466	397	409
Commercial real estate | Owner occupied | Adoption of ASC 326
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Impact of adoption ASC 326				(475)	(475)
Commercial real estate | Non-owner occupied
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,469	1,376	1,467	1,289	1,289
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	1,469	1,376	1,467	1,289	1,289
Provision for (Recovery of) Credit Losses	14	59	16	(46)	14
Ending Balance	1,483	1,435	1,483	1,435	1,467
Commercial real estate | Non-owner occupied | Adoption of ASC 326
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Impact of adoption ASC 326				192	192
Commercial real estate | Multifamily
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	84	44	44	33	33
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	84	44	44	33	33
Provision for (Recovery of) Credit Losses	(10)		30	4	(4)
Ending Balance	74	44	74	44	44
Commercial real estate | Multifamily | Adoption of ASC 326
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Impact of adoption ASC 326				7	7
Commercial real estate | Farmland
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1		3
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	1		3
Provision for (Recovery of) Credit Losses		3	(2)	3	(3)
Ending Balance	1	3	1	3	3
Consumer real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	427	361	432	185	185
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	427	361	432	185	185
Provision for (Recovery of) Credit Losses	(4)	29	(134)	73	(103)
Recoveries	2	6	127	13	19
Ending Balance	425	396	425	396	432
Consumer real estate | Adoption of ASC 326
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Impact of adoption ASC 326				125	125
Consumer real estate | Home equity lines
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	32	32	40	11	11
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	32	32	40	11	11
Provision for (Recovery of) Credit Losses	1	2	(17)	(1)	(5)
Recoveries			10
Ending Balance	33	34	33	34	40
Consumer real estate | Home equity lines | Adoption of ASC 326
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Impact of adoption ASC 326				24	24
Consumer real estate | First deed of trust
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	292	245	293	131	131
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	292	245	293	131	131
Provision for (Recovery of) Credit Losses	(14)	24	(17)	61	(83)
Recoveries	1	1	3	2	3
Ending Balance	279	270	279	270	293
Consumer real estate | First deed of trust | Adoption of ASC 326
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Impact of adoption ASC 326				76	76
Consumer real estate | Second deed of trust
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	103	84	99	43	43
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	103	84	99	43	43
Provision for (Recovery of) Credit Losses	9	3	(100)	13	(15)
Recoveries	1	5	114	11	16
Ending Balance	113	92	113	92	99
Consumer real estate | Second deed of trust | Adoption of ASC 326
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Impact of adoption ASC 326				25	25
Consumer real estate | Consumer Other and Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance			57
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance			57
Ending Balance					57
Commercial and industrial loans | Commercial and industrial loans (except those secured by real estate)
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	726	673	640	576	576
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	726	673	640	576	576
Provision for (Recovery of) Credit Losses	(24)	(223)	55	(139)	110
Recoveries	30	160	37	172	173
Ending Balance	732	610	732	610	640
Commercial and industrial loans | Commercial and industrial loans (except those secured by real estate) | Adoption of ASC 326
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Impact of adoption ASC 326				1	1
Commercial and industrial loans | Student loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	45	44	57	52	52
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	45	44	57	52	52
Provision for (Recovery of) Credit Losses	1	16		15	(35)
Charge-offs			(16)	(21)	(30)
Charge-offs	(5)	(14)			(30)
Ending Balance	41	46	41	46	57
Commercial and industrial loans | Consumer Other and Unallocated [Member]
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Ending Balance	164		164
Commercial and industrial loans | Consumer and other
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	34	34	36	37	37
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	34	34	36	37	37
Provision for (Recovery of) Credit Losses	(1)	3	(3)	5	(7)
Charge-offs				(2)	(3)
Charge-offs		(2)			(3)
Recoveries	1		1
Ending Balance	34	35	34	35	36
Commercial and industrial loans | Consumer and other | Adoption of ASC 326
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Impact of adoption ASC 326				(5)	(5)
Commercial and industrial loans | Unallocated
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	144	16	21	60	60
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	144	16	21	60	60
Provision for (Recovery of) Credit Losses	(14)	6	109	(29)	30
Ending Balance	$ 130	$ 22	$ 130	22	21
Commercial and industrial loans | Unallocated | Adoption of ASC 326
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Impact of adoption ASC 326				$ (9)	$ (9)