Fair value - Carrying amounts and estimated fair value of the company's (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Sep. 30, 2023	Dec. 31, 2022
Financial assets
Investment securities available for sale, at fair value	$ 82,784	$ 105,585
Loans held for sale	$ 7,000	$ 5,000
Fair Value, Inputs, Level 1 [Member] | Reported Value Measurement [Member]
Financial assets
Cash			$ 13,073	$ 10,383
Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value Measurement [Member]
Financial assets
Cash			13,073	10,383
Fair Value, Inputs, Level 2 [Member] | Reported Value Measurement [Member]
Financial assets
Cash equivalents			19,323	7,331
Investment securities available for sale, at fair value			82,284	105,085
Federal Home Loan Bank stock			2,644	2,644
Loans held for sale			7,019	4,983
Bank owned life insurance			13,198	13,120
Accrued interest receivable			3,531	3,827
Interest rate lock commitments			293	271
Financial liabilities
Deposits			620,269	605,345
FHLB borrowings			40,000	45,000
Trust preferred securities			8,764	8,764
Other borrowings			5,700	5,700
Accrued interest payable			406	210
Forward sales commitment			42	506
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value Measurement [Member]
Financial assets
Cash equivalents			19,323	7,331
Investment securities available for sale, at fair value			82,284	105,085
Federal Home Loan Bank stock			2,644	2,644
Loans held for sale			7,019	4,983
Bank owned life insurance			13,198	13,120
Accrued interest receivable			3,531	3,827
Interest rate lock commitments			293	271
Financial liabilities
Deposits			620,673	605,226
FHLB borrowings			39,886	44,999
Trust preferred securities			8,969	8,848
Other borrowings			5,700	5,700
Accrued interest payable			406	210
Forward sales commitment			42	506
Fair Value, Inputs, Level 3 [Member] | Reported Value Measurement [Member]
Financial assets
Investment securities available for sale, at fair value			500	500
Loans			591,338	575,008
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value Measurement [Member]
Financial assets
Investment securities available for sale, at fair value			500	500
Loans			$ 567,741	$ 547,935