Loans and allowance for credit losses - Allowance for credit losses on loans losses (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 3,423	$ 3,370	$ 3,370
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	3,423	3,370	3,370
Impact of adoption ASC 326			(127)
Provision for (Recovery of) Credit Losses			(21)
Charge-offs	(6)		(33)
Recoveries	20		192
Ending Balance	3,574	3,270	3,423
Adoption of ASC 326
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Provision for (Recovery of) Credit Losses	137
Construction and land development
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	314	271	271
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	314	271	271
Impact of adoption ASC 326			37
Provision for (Recovery of) Credit Losses		7	(6)
Ending Balance	259	315	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
Provision for (Recovery of) Credit Losses	(55)
Construction and land development | Residential
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	86	79	79
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	86	79	79
Impact of adoption ASC 326			3
Provision for (Recovery of) Credit Losses		(31)	(4)
Ending Balance	57	51	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
Provision for (Recovery of) Credit Losses	(29)
Construction and land development | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	228	192	192
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	228	192	192
Impact of adoption ASC 326			34
Provision for (Recovery of) Credit Losses		38	(2)
Ending Balance	202	264	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
Provision for (Recovery of) Credit Losses	(26)
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,923	2,189	2,189
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	1,923	2,189	2,189
Impact of adoption ASC 326			(276)
Provision for (Recovery of) Credit Losses		(22)	(10)
Ending Balance	2,119	1,891	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)
Provision for (Recovery of) Credit Losses	196
Commercial real estate | Owner occupied
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	409	867	867
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	409	867	867
Impact of adoption ASC 326			(475)
Provision for (Recovery of) Credit Losses		(1)	(17)
Ending Balance	437	391	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)
Provision for (Recovery of) Credit Losses	28
Commercial real estate | Non-owner occupied
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,467	1,289	1,289
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	1,467	1,289	1,289
Impact of adoption ASC 326			192
Provision for (Recovery of) Credit Losses		(21)	14
Ending Balance	1,596	1,460	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
Provision for (Recovery of) Credit Losses	129
Commercial real estate | Multifamily
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	44	33	33
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	44	33	33
Impact of adoption ASC 326			7
Provision for (Recovery of) Credit Losses			(4)
Ending Balance	86	40	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
Provision for (Recovery of) Credit Losses	42
Commercial real estate | Farmland
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	3
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	3
Provision for (Recovery of) Credit Losses			(3)
Ending Balance			3
Commercial real estate | Farmland | Adoption of ASC 326
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Provision for (Recovery of) Credit Losses	(3)
Consumer real estate secured by 1-4 family residential
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	432	185	185
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	432	185	185
Impact of adoption ASC 326			125
Provision for (Recovery of) Credit Losses		9	(103)
Recoveries	16	3	19
Ending Balance	428	322	432
Consumer real estate secured by 1-4 family residential | Adoption of ASC 326
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Impact of adoption ASC 326		125
Provision for (Recovery of) Credit Losses	(20)
Consumer real estate secured by 1-4 family residential | Home equity lines
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	40	11	11
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	40	11	11
Impact of adoption ASC 326			24
Provision for (Recovery of) Credit Losses		(2)	(5)
Recoveries	10
Ending Balance	32	33	40
Consumer real estate secured by 1-4 family residential | Home equity lines | Adoption of ASC 326
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Impact of adoption ASC 326		24
Provision for (Recovery of) Credit Losses	(18)
Consumer real estate secured by 1-4 family residential | First deed of trust
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	293	131	131
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	293	131	131
Impact of adoption ASC 326			76
Provision for (Recovery of) Credit Losses		6	(83)
Recoveries	1	1	3
Ending Balance	298	214	293
Consumer real estate secured by 1-4 family residential | 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
Provision for (Recovery of) Credit Losses	4
Consumer real estate secured by 1-4 family residential | Second deed of trust
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	99	43	43
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	99	43	43
Impact of adoption ASC 326			25
Provision for (Recovery of) Credit Losses		5	(15)
Recoveries	5	2	16
Ending Balance	98	75	99
Consumer real estate secured by 1-4 family residential | 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
Provision for (Recovery of) Credit Losses	(6)
Consumer real estate secured by 1-4 family residential | 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
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance		3,370	3,370
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance		3,370	3,370
Provision for (Recovery of) Credit Losses		23
Charge-offs		(3)
Recoveries		9
Ending Balance		3,272
Commercial and industrial loans | Adoption of ASC 326
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Impact of adoption ASC 326		(127)
Commercial and industrial loans | Commercial and industrial loans (except those secured by real estate)
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	640	576	576
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	640	576	576
Impact of adoption ASC 326			1
Provision for (Recovery of) Credit Losses		(34)	110
Recoveries	4	6	173
Ending Balance	666	549	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
Provision for (Recovery of) Credit Losses	22
Commercial and industrial loans | Student loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	57	52	52
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	57	52	52
Provision for (Recovery of) Credit Losses		63	(35)
Charge-offs	(6)	(3)	(30)
Ending Balance	55	112	57
Commercial and industrial loans | Student loans | Adoption of ASC 326
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Provision for (Recovery of) Credit Losses	4
Commercial and industrial loans | Consumer Other and Unallocated [Member]
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Ending Balance	47
Commercial and industrial loans | Consumer and other
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	36	37	37
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	36	37	37
Impact of adoption ASC 326			(5)
Provision for (Recovery of) Credit Losses		2	(7)
Charge-offs			(3)
Ending Balance	36	34	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)
Commercial and industrial loans | Unallocated
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	21	60	60
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	21	60	60
Impact of adoption ASC 326			(9)
Provision for (Recovery of) Credit Losses		(2)	30
Ending Balance	11	49	$ 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)
Provision for (Recovery of) Credit Losses	$ (10)