Investments in debt and equity securities - Debt Securities According to Contractual Terms (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Amortized costs
In one year or less	$ 85,105
After one year through five years	341,785
After five years through ten years	177,015
After ten years	16,901
Amortized costs	620,806	$ 631,294
Fair values
In one year or less	84,346
After one year through five years	327,413
After five years through ten years	169,663
After ten years	15,635
Fair values	$ 597,057	$ 610,236