Fair value measurements - Available-for-Sale Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023	Jun. 30, 2023
Available-for-sale securities [Abstract]
Cost	$ 11,897	$ 11,755	$ 11,633
Gross Unrealized Gains	57	45	5
Gross Unrealized Losses	482	478	697
Fair Value	11,472	11,322	10,941
Mortgage-backed securities
Available-for-sale securities [Abstract]
Cost	8,091	8,234	8,542
Gross Unrealized Gains	3	17	0
Gross Unrealized Losses	482	470	651
Fair Value	7,612	7,781	7,891
U.S. Treasury securities
Available-for-sale securities [Abstract]
Cost	3,806	3,521	3,091
Gross Unrealized Gains	54	28	5
Gross Unrealized Losses	0	8	46
Fair Value	$ 3,860	$ 3,541	$ 3,050