Loans and allowance for loan losses - Allowance for loan losses (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance			$ 3,423,000
Provision for (Recovery of) Loan Losses	$ 100,000		(300,000)	$ (500,000)
Ending Balance	3,370,000		3,370,000		$ 3,423,000
Consumer Real Estate Secured By 1-4 Family Residential
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				269,000	269,000
Provision for (Recovery of) Loan Losses				(31,000)
Charge-offs				(84,000)
Recoveries				58,000
Ending Balance		$ 212,000		212,000
Consumer and other
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance			451,000
Ending Balance	82,000		82,000		451,000
Construction and land development
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	228,000	269,000	286,000	499,000	499,000
Provision for (Recovery of) Loan Losses	16,000	38,000	(42,000)	(192,000)	(213,000)
Ending Balance	244,000	307,000	244,000	307,000	286,000
Construction and land development | Residential
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	57,000	66,000	57,000	214,000	214,000
Provision for (Recovery of) Loan Losses	12,000	10,000	12,000	(138,000)	(157,000)
Ending Balance	69,000	76,000	69,000	76,000	57,000
Construction and land development | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	171,000	203,000	229,000	285,000	285,000
Provision for (Recovery of) Loan Losses	4,000	28,000	(54,000)	(54,000)	(56,000)
Ending Balance	175,000	231,000	175,000	231,000	229,000
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	2,187,000	1,898,000	1,953,000	2,517,000	2,517,000
Provision for (Recovery of) Loan Losses	29,000	89,000	263,000	(544,000)	(578,000)
Recoveries				14,000	14,000
Ending Balance	2,216,000	1,987,000	2,216,000	1,987,000	1,953,000
Commercial real estate | Owner occupied
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	868,000	802,000	833,000	1,047,000	1,047,000
Provision for (Recovery of) Loan Losses	7,000	58,000	42,000	(187,000)	(214,000)
Ending Balance	875,000	860,000	875,000	860,000	833,000
Commercial real estate | Non-owner occupied
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	1,267,000	1,059,000	1,083,000	1,421,000	1,421,000
Provision for (Recovery of) Loan Losses	40,000	30,000	224,000	(346,000)	(352,000)
Recoveries				14,000	14,000
Ending Balance	1,307,000	1,089,000	1,307,000	1,089,000	1,083,000
Commercial real estate | Multifamily
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	50,000	35,000	35,000	47,000	47,000
Provision for (Recovery of) Loan Losses	(17,000)	1,000	(2,000)	(11,000)	(12,000)
Ending Balance	33,000	36,000	33,000	36,000	35,000
Commercial real estate | Farmland
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	2,000	2,000	2,000	2,000	2,000
Provision for (Recovery of) Loan Losses	(1,000)		(1,000)
Ending Balance	1,000	2,000	1,000	2,000	2,000
Commercial real estate | Home equity lines
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	12,000		12,000	24,000	24,000
Provision for (Recovery of) Loan Losses			(58,000)	(23,000)	(23,000)
Recoveries			58,000	10,000	11,000
Ending Balance	12,000	11,000	12,000	11,000	12,000
Commercial real estate | Consumer Real Estate Secured By 1-4 Family Residential
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance			182,000	269,000	269,000
Provision for (Recovery of) Loan Losses					(76,000)
Charge-offs					(84,000)
Recoveries					73,000
Ending Balance					182,000
Commercial real estate | First deed of trust
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	114,000
Provision for (Recovery of) Loan Losses	13,000
Recoveries	2,000
Ending Balance	129,000		129,000
Commercial real estate | Second deed of trust
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	49,000
Provision for (Recovery of) Loan Losses	(11,000)
Charge-offs	(27,000)
Recoveries	27,000
Ending Balance	38,000		38,000
Consumer real estate secured by 1-4 family residential
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	175,000	196,000	182,000
Provision for (Recovery of) Loan Losses	2,000	(6,000)	(368,000)
Charge-offs	(27,000)		(27,000)
Recoveries	29,000	22,000	392,000
Ending Balance	179,000	212,000	179,000	212,000	182,000
Consumer real estate secured by 1-4 family residential | Home equity lines
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance		11,000	12,000
Ending Balance	12,000	11,000	12,000	11,000	12,000
Consumer real estate secured by 1-4 family residential | First deed of trust
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance		113,000	123,000	166,000	166,000
Provision for (Recovery of) Loan Losses		(3,000)	2,000	(65,000)	(54,000)
Recoveries		1,000	4,000	10,000	11,000
Ending Balance	129,000	111,000	129,000	111,000	123,000
Consumer real estate secured by 1-4 family residential | Second deed of trust
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance		72,000	47,000	79,000	79,000
Provision for (Recovery of) Loan Losses		(3,000)	(312,000)	57,000	1,000
Charge-offs			(27,000)	(84,000)	(84,000)
Recoveries		21,000	330,000	38,000	51,000
Ending Balance	38,000	90,000	38,000	90,000	47,000
Commercial and industrial loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	3,423,000	3,429,000	3,423,000	3,970,000	3,970,000
Provision for (Recovery of) Loan Losses	100,000		(300,000)	(500,000)	(500,000)
Charge-offs	(187,000)	(11,000)	(209,000)	(126,000)	(165,000)
Recoveries	34,000	25,000	456,000	99,000	118,000
Ending Balance	3,370,000	3,443,000	3,370,000	3,443,000	3,423,000
Commercial and industrial loans | Commercial and industrial loans (except those secured by real estate)
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	533,000	422,000	486,000	408,000	408,000
Provision for (Recovery of) Loan Losses	201,000	55,000	189,000	45,000	47,000
Charge-offs	(157,000)		(157,000)
Recoveries	5,000	3,000	64,000	27,000	31,000
Ending Balance	582,000	480,000	582,000	480,000	486,000
Commercial and industrial loans | Guaranteed student loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	60,000	80,000	65,000	87,000	87,000
Provision for (Recovery of) Loan Losses	9,000	1,000	26,000	7,000	13,000
Charge-offs	(2,000)	(11,000)	(24,000)	(24,000)	(35,000)
Ending Balance	67,000	70,000	67,000	70,000	65,000
Commercial and industrial loans | Consumer and other
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	45,000	36,000	29,000	36,000	36,000
Provision for (Recovery of) Loan Losses	(7,000)	(4,000)	9,000	14,000	39,000
Charge-offs	(1,000)		(1,000)	(18,000)	(46,000)
Ending Balance	37,000	32,000	37,000	32,000	29,000
Commercial and industrial loans | Unallocated
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	195,000	528,000	422,000	154,000	154,000
Provision for (Recovery of) Loan Losses	(150,000)	(173,000)	(377,000)	201,000	268,000
Ending Balance	$ 45,000	$ 355,000	$ 45,000	$ 355,000	$ 422,000