Loans and allowances for loan losses - Classified by type (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Sep. 30, 2023	Mar. 31, 2023	Dec. 31, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items]
Less: allowance for credit losses	$ (3,574)	$ (3,423)		$ (3,270)	$ (3,370)
Percentage of class of loans to loan portfolio (in percent)	100.00%	100.00%
Loans
Total loans	$ 591,338	$ 575,008	$ 591,338
Deferred (fees) and costs, net	750	803
Less: allowance for credit losses	(3,574)	(3,423)		(3,270)	(3,370)
Total loans, net	588,514	572,388
Construction and land development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Less: allowance for credit losses	$ (259)	$ (314)	(259)	(315)	(271)
Percentage of class of loans to loan portfolio (in percent)	7.36%	8.26%
Loans
Total loans	$ 43,514	$ 47,495	43,514
Less: allowance for credit losses	(259)	(314)	(259)	(315)	(271)
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Less: allowance for credit losses	$ (2,119)	$ (1,923)	(2,119)	(1,891)	(2,189)
Percentage of class of loans to loan portfolio (in percent)	51.61%	50.54%
Loans
Total loans	$ 305,215	$ 290,590	305,215
Less: allowance for credit losses	(2,119)	(1,923)	(2,119)	(1,891)	(2,189)
Consumer real estate secured by 1-4 family residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Less: allowance for credit losses	$ (428)	$ (432)	(428)	(322)	(185)
Percentage of class of loans to loan portfolio (in percent)	21.92%	22.35%
Loans
Total loans	$ 129,631	$ 128,532	129,631
Less: allowance for credit losses	(428)	(432)	(428)	(322)	(185)
Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Less: allowance for credit losses				(3,272)	(3,370)
Loans
Less: allowance for credit losses				(3,272)	(3,370)
Residential | Construction and land development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Less: allowance for credit losses	$ (57)	$ (86)		(51)	(79)
Percentage of class of loans to loan portfolio (in percent)	1.53%	1.82%
Loans
Total loans	$ 9,077	$ 10,471	9,077
Less: allowance for credit losses	(57)	(86)		(51)	(79)
Commercial | Construction and land development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Less: allowance for credit losses	$ (202)	$ (228)		(264)	(192)
Percentage of class of loans to loan portfolio (in percent)	5.83%	6.44%
Loans
Total loans	$ 34,437	$ 37,024	34,437
Less: allowance for credit losses	(202)	(228)		(264)	(192)
Owner occupied | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Less: allowance for credit losses	$ (437)	$ (409)		(391)	(867)
Percentage of class of loans to loan portfolio (in percent)	20.53%	21.33%
Loans
Total loans	$ 121,429	$ 122,666	121,429
Less: allowance for credit losses	(437)	(409)		(391)	(867)
Non-owner occupied | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Less: allowance for credit losses	$ (1,596)	$ (1,467)		(1,460)	(1,289)
Percentage of class of loans to loan portfolio (in percent)	27.99%	26.93%
Loans
Total loans	$ 165,508	$ 154,855	165,508
Less: allowance for credit losses	(1,596)	(1,467)		(1,460)	(1,289)
Multifamily | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Less: allowance for credit losses	$ (86)	$ (44)		(40)	(33)
Percentage of class of loans to loan portfolio (in percent)	3.09%	2.22%
Loans
Total loans	$ 18,254	$ 12,743	18,254
Less: allowance for credit losses	$ (86)	(44)		(40)	(33)
Farmland | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Less: allowance for credit losses		$ (3)
Percentage of class of loans to loan portfolio (in percent)	0.00%	0.06%
Loans
Total loans	$ 24	$ 326	24
Less: allowance for credit losses		(3)
Home equity lines | Consumer real estate secured by 1-4 family residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Less: allowance for credit losses	$ (32)	$ (40)		(33)	(11)
Percentage of class of loans to loan portfolio (in percent)	3.67%	3.75%
Loans
Total loans	$ 21,682	$ 21,557	21,682
Less: allowance for credit losses	(32)	(40)		(33)	(11)
First deed of trust | Consumer real estate secured by 1-4 family residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Less: allowance for credit losses	$ (298)	$ (293)		(214)	(131)
Percentage of class of loans to loan portfolio (in percent)	16.23%	16.63%
Loans
Total loans	$ 95,994	$ 95,638	95,994
Less: allowance for credit losses	(298)	(293)		(214)	(131)
Second deed of trust | Consumer real estate secured by 1-4 family residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Less: allowance for credit losses	$ (98)	$ (99)		(75)	(43)
Percentage of class of loans to loan portfolio (in percent)	2.02%	1.97%
Loans
Total loans	$ 11,955	$ 11,337	11,955
Less: allowance for credit losses	(98)	(99)		(75)	(43)
Commercial and industrial loans (except those secured by real estate) | Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Less: allowance for credit losses	$ (666)	$ (640)		(549)	(576)
Percentage of class of loans to loan portfolio (in percent)	15.66%	14.99%
Loans
Total loans	$ 92,600	$ 86,203	92,600
Less: allowance for credit losses	(666)	(640)		(549)	(576)
Guaranteed student loans | Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Less: allowance for credit losses	$ (55)	$ (57)		(112)	(52)
Percentage of class of loans to loan portfolio (in percent)	2.67%	3.12%
Loans
Total loans	$ 15,782	$ 17,923	15,782
Less: allowance for credit losses	(55)	(57)		(112)	(52)
Consumer and other | Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Less: allowance for credit losses	$ (36)	$ (36)		(34)	(37)
Percentage of class of loans to loan portfolio (in percent)	0.78%	0.74%
Loans
Total loans	$ 4,596	$ 4,265	$ 4,596
Less: allowance for credit losses	$ (36)	$ (36)		$ (34)	$ (37)