Bank call loans - Schedule of Bank Call Loans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Bank Call Loans [Abstract]
Year-end balance	$ 76,800	$ 252,100
Weighted interest rate (at end of year) (as a percent)	4.60%	5.12%
Maximum balance (at any month-end)	$ 439,600	$ 288,200
Average amount outstanding (during the year)	$ 269,635	$ 167,691
Average interest rate (during the year) (as a percent)	5.00%	5.44%