Investments in debt and equity securities - Debt Securities According Contractual Terms (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Amortized costs
In one year or less	$ 71,014
After one year through five years	330,380
After five years through ten years	146,214
After ten years	30,557
Amortized costs	578,165	$ 599,412
Fair values
In one year or less	71,860
After one year through five years	334,632
After five years through ten years	150,137
After ten years	33,143
Fair values	$ 589,772	$ 631,386