Securities - Contractual maturities of debt securities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Amortized Cost
Due in one year or less	$ 9,687
Due after one but within five years	44,613
Due after five but within ten years	101,584
Due after ten years	393,065
Total of securities having specified maturity period	548,949
Mortgage-backed securities and collateralized mortgage obligations	891,882
Amortized Cost	1,440,831	$ 1,498,626
Fair Value
Due in one year or less	9,572
Due after one but within five years	42,259
Due after five but within ten years	96,076
Due after ten years	332,382
Total of securities having specified maturities period	480,289
Mortgage-backed securities and collateralized mortgage obligations	744,930
TOTAL	$ 1,225,219	$ 1,330,481