Furniture, equipment and leasehold improvements - Summary of Office Facilities Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Property, Plant and Equipment [Line Items]
Office facilities, gross	$ 130,578	$ 126,606
Less accumulated depreciation	(92,390)	(82,732)
Total	38,188	43,874
Furniture, fixtures and equipment
Property, Plant and Equipment [Line Items]
Office facilities, gross	65,979	63,473
Leasehold improvements
Property, Plant and Equipment [Line Items]
Office facilities, gross	$ 64,599	$ 63,133