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	Sep. 30, 2025	Dec. 31, 2024
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
U.S. Treasury securities	$ 1,208,900	$ 999,809
Corporate equities	286,694	$ 235,498
Overnight and Open
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross amount of recognized liabilities for repurchase agreements and securities loaned	$ 1,495,594