Investments in debt and equity securities - Debt Securities According to Contractual Terms (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Amortized costs
In one year or less	$ 59,019
After one year through five years	375,721
After five years through ten years	148,716
After ten years	30,757
Amortized costs, total	614,213	$ 599,412
Fair values
In one year or less	59,695
After one year through five years	385,551
After five years through ten years	156,299
After ten years	33,617
Fair values, total	$ 635,162	$ 631,386