Furniture, equipment and leasehold improvements - Summary of Office Facilities Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024
Property, Plant and Equipment [Line Items]
Office facilities, gross	$ 134,364	$ 130,578
Less accumulated depreciation	(101,962)	(92,390)
Total	32,402	38,188
Furniture, fixtures and equipment
Property, Plant and Equipment [Line Items]
Office facilities, gross	68,866	65,979
Leasehold improvements
Property, Plant and Equipment [Line Items]
Office facilities, gross	$ 65,498	$ 64,599