Principles of presentation - Impact of ASC 326 (Details) - USD ($)	Jun. 30, 2023	Mar. 31, 2023	Jan. 01, 2023	Dec. 31, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021
Allowance for credit losses				$ 3,370,000	$ 3,423,000	$ 3,403,000	$ 3,423,000
Total Allowance for credit losses	$ 3,256,000	$ 3,272,000
Allowance for credit losses on unfunded credit exposure	277,000
Total Allowance for credit losses	3,530,000
Retained earnings	13,142,000			10,957,000
Adoption of ASC 326
Allowance for credit losses				(127,000)
Accounting Standards Update 2016-13 | Adoption of ASC 326
Total Allowance for credit losses			$ (127,000)
Allowance for credit losses on unfunded credit exposure			277,000
Total Allowance for credit losses			150,000
Retained earnings			(119,000)
Accounting Standards Update 2016-13 | Cumulative Effect, Period of Adoption, Adjusted Balance
Total Allowance for credit losses			3,243,000
Allowance for credit losses on unfunded credit exposure			277,000
Total Allowance for credit losses			3,520,000
Accounting Standards Update 2022-02
Allowance for credit loss on financing receivable, non-collateral dependent troubled debt restructuring loans			(8,000)
Construction and land development
Allowance for credit losses				271,000	228,000	245,000	286,000
Total Allowance for credit losses	328,000	315,000
Construction and land development | Adoption of ASC 326
Allowance for credit losses				37,000
Construction and land development | Accounting Standards Update 2016-13 | Adoption of ASC 326
Total Allowance for credit losses			37,000
Construction and land development | Accounting Standards Update 2016-13 | Cumulative Effect, Period of Adoption, Adjusted Balance
Total Allowance for credit losses			308,000
Construction and land development | Residential
Allowance for credit losses				79,000	57,000	46,000	57,000
Total Allowance for credit losses	61,000	51,000
Construction and land development | Residential | Adoption of ASC 326
Allowance for credit losses				3,000
Construction and land development | Residential | Accounting Standards Update 2016-13 | Adoption of ASC 326
Total Allowance for credit losses			3,000
Construction and land development | Residential | Accounting Standards Update 2016-13 | Cumulative Effect, Period of Adoption, Adjusted Balance
Total Allowance for credit losses			82,000
Construction and land development | Commercial
Allowance for credit losses				192,000	171,000	199,000	229,000
Total Allowance for credit losses	267,000	264,000
Construction and land development | Commercial | Adoption of ASC 326
Allowance for credit losses				34,000
Construction and land development | Commercial | Accounting Standards Update 2016-13 | Adoption of ASC 326
Total Allowance for credit losses			34,000
Construction and land development | Commercial | Accounting Standards Update 2016-13 | Cumulative Effect, Period of Adoption, Adjusted Balance
Total Allowance for credit losses			226,000
Commercial real estate
Allowance for credit losses				2,189,000	2,187,000	2,037,000	1,953,000
Total Allowance for credit losses	1,795,000	1,891,000
Commercial real estate | Adoption of ASC 326
Allowance for credit losses				(276,000)
Commercial real estate | Accounting Standards Update 2016-13 | Adoption of ASC 326
Total Allowance for credit losses			(276,000)
Commercial real estate | Accounting Standards Update 2016-13 | Cumulative Effect, Period of Adoption, Adjusted Balance
Total Allowance for credit losses			1,913,000
Commercial real estate | Owner occupied
Allowance for credit losses				867,000	868,000	892,000	833,000
Total Allowance for credit losses	379,000	391,000
Commercial real estate | Owner occupied | Adoption of ASC 326
Allowance for credit losses				(475,000)
Commercial real estate | Owner occupied | Accounting Standards Update 2016-13 | Adoption of ASC 326
Total Allowance for credit losses			(475,000)
Commercial real estate | Owner occupied | Accounting Standards Update 2016-13 | Cumulative Effect, Period of Adoption, Adjusted Balance
Total Allowance for credit losses			392,000
Commercial real estate | Non-owner occupied
Allowance for credit losses				1,289,000	1,267,000	1,106,000	1,083,000
Total Allowance for credit losses	1,376,000	1,460,000
Commercial real estate | Non-owner occupied | Adoption of ASC 326
Allowance for credit losses				192,000
Commercial real estate | Non-owner occupied | Accounting Standards Update 2016-13 | Adoption of ASC 326
Total Allowance for credit losses			192,000
Commercial real estate | Non-owner occupied | Accounting Standards Update 2016-13 | Cumulative Effect, Period of Adoption, Adjusted Balance
Total Allowance for credit losses			1,481,000
Commercial real estate | Multifamily
Allowance for credit losses				33,000	50,000	37,000	35,000
Total Allowance for credit losses	40,000	40,000
Commercial real estate | Multifamily | Adoption of ASC 326
Allowance for credit losses				7,000
Commercial real estate | Multifamily | Accounting Standards Update 2016-13 | Adoption of ASC 326
Total Allowance for credit losses			7,000
Commercial real estate | Multifamily | Accounting Standards Update 2016-13 | Cumulative Effect, Period of Adoption, Adjusted Balance
Total Allowance for credit losses			40,000
Commercial real estate | Farmland
Allowance for credit losses					2,000	2,000	2,000
Consumer real estate secured by 1-4 family residential
Allowance for credit losses				185,000	175,000	210,000	182,000
Total Allowance for credit losses	365,000	322,000
Consumer real estate secured by 1-4 family residential | Adoption of ASC 326
Allowance for credit losses				125,000
Consumer real estate secured by 1-4 family residential | Accounting Standards Update 2016-13 | Adoption of ASC 326
Total Allowance for credit losses			125,000
Consumer real estate secured by 1-4 family residential | Accounting Standards Update 2016-13 | Cumulative Effect, Period of Adoption, Adjusted Balance
Total Allowance for credit losses			310,000
Consumer real estate secured by 1-4 family residential | Home equity lines
Allowance for credit losses				11,000	12,000	12,000	12,000
Total Allowance for credit losses	63,000	33,000
Consumer real estate secured by 1-4 family residential | Home equity lines | Adoption of ASC 326
Allowance for credit losses				24,000
Consumer real estate secured by 1-4 family residential | Home equity lines | Accounting Standards Update 2016-13 | Adoption of ASC 326
Total Allowance for credit losses			24,000
Consumer real estate secured by 1-4 family residential | Home equity lines | Accounting Standards Update 2016-13 | Cumulative Effect, Period of Adoption, Adjusted Balance
Total Allowance for credit losses			35,000
Consumer real estate secured by 1-4 family residential | First deed of trust
Allowance for credit losses				131,000	114,000	118,000	123,000
Total Allowance for credit losses	219,000	214,000
Consumer real estate secured by 1-4 family residential | First deed of trust | Adoption of ASC 326
Allowance for credit losses				76,000
Consumer real estate secured by 1-4 family residential | First deed of trust | Accounting Standards Update 2016-13 | Adoption of ASC 326
Total Allowance for credit losses			76,000
Consumer real estate secured by 1-4 family residential | First deed of trust | Accounting Standards Update 2016-13 | Cumulative Effect, Period of Adoption, Adjusted Balance
Total Allowance for credit losses			207,000
Consumer real estate secured by 1-4 family residential | Second deed of trust
Allowance for credit losses				43,000	49,000	80,000	47,000
Total Allowance for credit losses	83,000	75,000
Consumer real estate secured by 1-4 family residential | Second deed of trust | Adoption of ASC 326
Allowance for credit losses				25,000
Consumer real estate secured by 1-4 family residential | Second deed of trust | Accounting Standards Update 2016-13 | Adoption of ASC 326
Total Allowance for credit losses			25,000
Consumer real estate secured by 1-4 family residential | Second deed of trust | Accounting Standards Update 2016-13 | Cumulative Effect, Period of Adoption, Adjusted Balance
Total Allowance for credit losses			68,000
Consumer real estate secured by 1-4 family residential | Consumer and other
Allowance for credit losses				97,000
Total Allowance for credit losses	82,000
Commercial and industrial loans | Commercial and industrial loans (except those secured by real estate)
Allowance for credit losses				576,000	533,000	446,000	486,000
Total Allowance for credit losses	673,000	549,000
Commercial and industrial loans | Commercial and industrial loans (except those secured by real estate) | Adoption of ASC 326
Allowance for credit losses				1,000
Commercial and industrial loans | Commercial and industrial loans (except those secured by real estate) | Accounting Standards Update 2016-13 | Adoption of ASC 326
Total Allowance for credit losses			1,000
Commercial and industrial loans | Commercial and industrial loans (except those secured by real estate) | Accounting Standards Update 2016-13 | Cumulative Effect, Period of Adoption, Adjusted Balance
Total Allowance for credit losses			577,000
Commercial and industrial loans | Guaranteed student loans
Allowance for credit losses				52,000	60,000	63,000	65,000
Total Allowance for credit losses	13,000	112,000
Commercial and industrial loans | Guaranteed student loans | Accounting Standards Update 2016-13 | Cumulative Effect, Period of Adoption, Adjusted Balance
Total Allowance for credit losses			52,000
Commercial and industrial loans | Consumer and other
Allowance for credit losses				37,000	45,000	35,000	29,000
Total Allowance for credit losses	35,000	34,000
Commercial and industrial loans | Consumer and other | Adoption of ASC 326
Allowance for credit losses				(5,000)
Commercial and industrial loans | Consumer and other | Accounting Standards Update 2016-13 | Adoption of ASC 326
Total Allowance for credit losses			(5,000)
Commercial and industrial loans | Consumer and other | Accounting Standards Update 2016-13 | Cumulative Effect, Period of Adoption, Adjusted Balance
Total Allowance for credit losses			32,000
Commercial and industrial loans | Unallocated
Allowance for credit losses				60,000	$ 195,000	$ 367,000	$ 422,000
Total Allowance for credit losses	$ 47,000	$ 49,000
Commercial and industrial loans | Unallocated | Adoption of ASC 326
Allowance for credit losses				$ (9,000)
Commercial and industrial loans | Unallocated | Accounting Standards Update 2016-13 | Adoption of ASC 326
Total Allowance for credit losses			(9,000)
Commercial and industrial loans | Unallocated | Accounting Standards Update 2016-13 | Cumulative Effect, Period of Adoption, Adjusted Balance
Total Allowance for credit losses			$ 51,000