Fair value measurement - Assets measured at fair value on nonrecurring basis (Details) - Nonrecurring - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	$ 9,113	$ 9,933
Loans held-for-sales		8,080
Other real estate owned	5,457	3,067
Other foreclosed assets	44	30
Long-lived assets held-for-sale		686
Total assets measured at fair value on non-recurring basis	14,614	21,796
Loans - write-down	(3,087)	(9,580)
Loans held-for-sale - write-down		(224)
Other real estate owned - write down	(1,012)	(940)
Other foreclosed assets - write down	(14)	(1)
Long-lived asset held-for-sale - write down		(688)
Total assets measured - write down	(4,113)	(11,433)
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	0	0
Loans held-for-sales		0
Other real estate owned	0	0
Other foreclosed assets	0	0
Long-lived assets held-for-sale		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
Loans held-for-sales		0
Other real estate owned	0	0
Other foreclosed assets	0	0
Long-lived assets held-for-sale		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	9,113	9,933
Loans held-for-sales		8,080
Other real estate owned	5,457	3,067
Other foreclosed assets	44	30
Long-lived assets held-for-sale		686
Total assets measured at fair value on non-recurring basis	$ 14,614	$ 21,796