Loans and allowance for loan losses - Information on the risk rating of loans (Details) - USD ($)	Mar. 31, 2024	Dec. 31, 2023	Sep. 30, 2023
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 591,338,000	$ 575,008,000	$ 591,338,000
Total loans	281,000	291,000
Construction and land development
Financing Receivable, Recorded Investment [Line Items]
Total loans	43,514,000	47,495,000	43,514,000
Construction and land development | Residential
Financing Receivable, Recorded Investment [Line Items]
Total loans	9,077,000	10,471,000	9,077,000
Construction and land development | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	34,437,000	37,024,000	34,437,000
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	305,215,000	290,590,000	305,215,000
Commercial real estate | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Total loans	121,429,000	122,666,000	121,429,000
Commercial real estate | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Total loans	165,508,000	154,855,000	165,508,000
Commercial real estate | Multifamily
Financing Receivable, Recorded Investment [Line Items]
Total loans	18,254,000	12,743,000	18,254,000
Commercial real estate | Farmland
Financing Receivable, Recorded Investment [Line Items]
Total loans	24,000	326,000	24,000
Consumer real estate secured by 1-4 family residential
Financing Receivable, Recorded Investment [Line Items]
Total loans	129,631,000	128,532,000	129,631,000
Total loans	259,000	265,000
Consumer real estate secured by 1-4 family residential | Home equity lines
Financing Receivable, Recorded Investment [Line Items]
Total loans	21,682,000	21,557,000	21,682,000
Consumer real estate secured by 1-4 family residential | First deed of trust
Financing Receivable, Recorded Investment [Line Items]
Total loans	95,994,000	95,638,000	95,994,000
Total loans	159,000	160,000
Consumer real estate secured by 1-4 family residential | Second deed of trust
Financing Receivable, Recorded Investment [Line Items]
Total loans	11,955,000	11,337,000	11,955,000
Total loans	100,000	105,000
Commercial and industrial loans | Commercial and industrial loans (except those secured by real estate)
Financing Receivable, Recorded Investment [Line Items]
Total loans	92,600,000	86,203,000	92,600,000
Total loans	22,000	26,000
Commercial and industrial loans | Guaranteed student loans
Financing Receivable, Recorded Investment [Line Items]
Total loans	15,782,000	17,923,000	15,782,000
Commercial and industrial loans | Consumer and other
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 4,596,000	$ 4,265,000	$ 4,596,000