Collateralized transactions - Schedule of Disaggregation of Gross Obligation by Class of Collateral Pledged and Remaining Contractual Maturity of Repurchase Agreements and Securities Loaned Transactions (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
U.S. Treasury securities	$ 1,162,210	$ 1,172,957
Corporate equities	320,163	$ 370,331
Overnight and Open
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amount of recognized liabilities for repurchase agreements and securities loaned	$ 1,482,373