Investments in debt and equity securities - Schedule of Amortized Costs and Fair Values of Investments in Debt Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025
Debt Securities, Available-for-sale [Line Items]
Amortized costs	$ 554,775	$ 558,544
Fair values	551,161	558,488
Municipal
Debt Securities, Available-for-sale [Line Items]
Amortized costs	9,878	12,292
Fair values	9,870	12,274
Corporate
Debt Securities, Available-for-sale [Line Items]
Amortized costs	145,789	144,571
Fair values	143,285	143,621
Foreign
Debt Securities, Available-for-sale [Line Items]
Amortized costs	340,382	347,588
Fair values	339,350	348,084
U.S. Treasury Bonds
Debt Securities, Available-for-sale [Line Items]
Amortized costs	58,726	54,093
Fair values	$ 58,656	$ 54,509