Investments in debt and equity securities - Debt Securities According Contractual Terms (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Amortized costs
In one year or less	$ 101,047
After one year through five years	344,370
After five years through ten years	173,408
After ten years	12,469
Amortized costs	631,294	$ 646,728
Fair values
In one year or less	99,855
After one year through five years	330,077
After five years through ten years	168,804
After ten years	11,500
Fair values	$ 610,236	$ 611,934