Loans, net and allowance for credit losses - Net Deferred Loan Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Net deferred loan costs	$ 400	$ 300
Loans outstanding	3,100	3,200
Advances of loans receivable	1,300	1,100
Repayments of loans receivable	1,400	1,100
Number of related party loans classified as nonaccrual, past due, or restructured	0	0
Deposits from related parties	7,800	6,800
Net loans	2,828,002
Federal Home Loan Bank Advances [Member]
Amount of credit facility used to issue standby letters of credit to collateralize public fund deposits	1,200
Federal Reserve Bank Advances [Member]
Amount of credit facility used to issue standby letters of credit to collateralize public fund deposits	246,100
Asset Pledged as Collateral [Member] | Federal Home Loan Bank Advances [Member]
Net loans	1,800,000	1,600,000
Amount of credit facility used to issue standby letters of credit to collateralize public fund deposits	1,200,000	$ 1,200,000
Asset Pledged as Collateral [Member] | Federal Reserve Bank Advances [Member]
Net loans	$ 365,800