Fair value measurement - Assets measured at fair value on nonrecurring basis (Details) - Nonrecurring - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	$ 110	$ 1,629
Other real estate owned	1,416	2,330
Other foreclosed assets	105	15
Total assets measured at fair value on non-recurring basis	1,631	3,974
Loans - write-down	(2,172)	(3)
Other real estate owned - write down	(224)	(628)
Other foreclosed assets - write down	(41)	(4)
Total assets measured - write down	(2,437)	(635)
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	0	0
Other real estate owned	0	0
Other foreclosed assets	0	0
Total assets measured at fair value on non-recurring basis	0	0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	0	0
Other real estate owned	0	0
Other foreclosed assets	0	0
Total assets measured at fair value on non-recurring basis	0	0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	110	1,629
Other real estate owned	1,416	2,330
Other foreclosed assets	105	15
Total assets measured at fair value on non-recurring basis	$ 1,631	$ 3,974