Fair value measurements - Schedule of Available-for-Sale Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Dec. 31, 2024	Sep. 30, 2024
Available-for-sale securities [Abstract]
Cost	$ 11,960	$ 11,878	$ 12,001
Gross Unrealized Gains	48	84	115
Gross Unrealized Losses	233	384	312
Fair Value	11,775	11,578	11,804
Mortgage-backed securities
Available-for-sale securities [Abstract]
Cost	8,465	7,933	8,104
Gross Unrealized Gains	24	4	41
Gross Unrealized Losses	230	383	312
Fair Value	8,259	7,554	7,833
U.S. Treasury securities
Available-for-sale securities [Abstract]
Cost	3,495	3,945	3,897
Gross Unrealized Gains	24	80	74
Gross Unrealized Losses	3	1	0
Fair Value	$ 3,516	$ 4,024	$ 3,971