Fair value measurement - Assets measured at fair value on nonrecurring basis (Details) - Nonrecurring - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	$ 10,091	$ 11,215	$ 21,167
Other real estate owned	6,560	3,992	7,727
Other foreclosed assets	102	13	68
Long-lived assets held-for-sale		1,178	9,007
Trademark			156
Total assets measured at fair value on non-recurring basis	16,753	16,398	38,125
Loans - write-down	(3,157)	(2,067)	(3,721)
Other real estate owned - write down	(1,516)	(1,026)	(1,579)
Other foreclosed assets - write down	(28)	(1)	(33)
Long-lived asset held-for-sale - write down		(2,155)	(5,320)
Trademark - write down			(5,404)
Total assets measured - write down	(4,701)	(5,249)	(16,057)
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	0
Trademark			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	0
Trademark			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	10,091	11,215	21,167
Other real estate owned	6,560	3,992	7,727
Other foreclosed assets	102	13	68
Long-lived assets held-for-sale		1,178	9,007
Trademark			156
Total assets measured at fair value on non-recurring basis	$ 16,753	$ 16,398	$ 38,125