Securities - Contractual maturities of debt securities (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Amortized Cost
Due in one year or less	$ 8,551
Due after one but within five years	43,363
Due after five but within ten years	109,167
Due after ten years	374,043
Total of securities having specified maturity period	535,124
Mortgage-backed securities and collateralized mortgage obligations	850,987
Amortized Cost	1,386,111	$ 1,412,498
Fair Value
Due in one year or less	8,446
Due after one but within five years	41,503
Due after five but within ten years	105,859
Due after ten years	333,856
Total of securities having specified maturities period	489,664
Mortgage-backed securities and collateralized mortgage obligations	728,623
TOTAL	$ 1,218,287	$ 1,259,137