Investments in debt and equity securities - Debt Securities According to Contractual Terms (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Amortized costs
In one year or less	$ 105,848
After one year through five years	329,317
After five years through ten years	180,634
After ten years	12,354
Amortized costs	628,153	$ 646,728
Fair values
In one year or less	103,828
After one year through five years	306,479
After five years through ten years	164,702
After ten years	10,397
Fair values	$ 585,406	$ 611,934