Long-term debt - Long-term debt advances (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Debt Instrument
Long-term debt	$ 25,000	$ 555
Long-term 4.69% fixed rate debt due March 2023
Debt Instrument
Long-term debt		$ 555
Fixed interest rate (as a percent)		4.69%
Long-term 4.37% fixed rate debt due March 2025
Debt Instrument
Long-term debt	$ 10,000
Fixed interest rate (as a percent)	4.37%
Long-term 4.20% fixed rate debt due March 2026
Debt Instrument
Long-term debt	$ 15,000
Fixed interest rate (as a percent)	4.20%