Short-term borrowings - Additional Information (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Short-term borrowings
Maximum borrowing capacity	$ 18,000	$ 18,000
Outstanding amount in borrowings	0	0
Net loans	2,828,002
Total investment securities	483,876	568,992
FHLB Advances
Short-term borrowings
Amount of credit facility used to issue standby letters of credit to collateralize public fund deposits	1,200
Federal Reserve Bank Advances
Short-term borrowings
Amount of credit facility used to issue standby letters of credit to collateralize public fund deposits	246,100
Assets pledged as collateral | FHLB Advances
Short-term borrowings
Amount of credit facility used to issue standby letters of credit to collateralize public fund deposits	1,200,000	1,200,000
Net loans	1,800,000	1,600,000
Assets pledged as collateral | Federal Reserve Bank Advances
Short-term borrowings
Net loans	365,800
Assets pledged as collateral | Borrow in Custody Program
Short-term borrowings
Net loans	365,800	349,900
Assets pledged as collateral | Bank Term Funding Program
Short-term borrowings
Total investment securities	191,000
Assets pledged as collateral | Discount Window
Short-term borrowings
Total investment securities	11	24
Federal Reserve Bank Discount Window
Short-term borrowings
Maximum borrowing capacity	257,400
Bank Term Funding Program
Short-term borrowings
Maximum borrowing capacity	191,000
Borrow in Custody Program
Short-term borrowings
Amount of credit facility used to issue standby letters of credit to collateralize public fund deposits	246,100	$ 232,200
Peoples Bank
Short-term borrowings
Maximum borrowing capacity	1,200,000
Outstanding amount in borrowings	25,000
Amount of credit facility used to issue standby letters of credit to collateralize public fund deposits	$ 345,400