Fair value measurement - Assets measured at fair value on nonrecurring basis (Details) - Nonrecurring - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	$ 6,808	$ 10,091	$ 11,215
Other real estate owned	6,050	6,560	3,992
Other foreclosed assets	134	102	13
Long-lived assets held-for-sale			1,178
Total assets measured at fair value on non-recurring basis	12,992	16,753	16,398
Loans - write-down	(939)	(3,157)	(2,067)
Other real estate owned - write down	(1,934)	(1,516)	(1,026)
Other foreclosed assets - write down	(55)	(28)	(1)
Long-lived asset held-for-sale - write down			(2,155)
Total assets measured - write down	(2,928)	(4,701)	(5,249)
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	0	0	0
Other real estate owned	0	0	0
Other foreclosed assets	0	0	0
Long-lived assets held-for-sale			0
Total assets measured at fair value on non-recurring basis	0	0	0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	0	0	0
Other real estate owned	0	0	0
Other foreclosed assets	0	0	0
Long-lived assets held-for-sale			0
Total assets measured at fair value on non-recurring basis	0	0	0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	6,808	10,091	11,215
Other real estate owned	6,050	6,560	3,992
Other foreclosed assets	134	102	13
Long-lived assets held-for-sale			1,178
Total assets measured at fair value on non-recurring basis	$ 12,992	$ 16,753	$ 16,398