Fair value measurements - Schedule of Fair Value Amounts of Derivative Instruments and their Effect on Consolidated Income Statements (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Derivative Instruments, Gain (Loss) [Line Items]
Recognized in Income on Derivatives (pre-tax)	$ 3,929	$ (1,138)
Commodity contracts | Principal transactions revenue, net | Futures
Derivative Instruments, Gain (Loss) [Line Items]
Recognized in Income on Derivatives (pre-tax)	3,929	$ (1,138)
Other contracts | Principal transactions revenue, net | TBAs
Derivative Instruments, Gain (Loss) [Line Items]
Recognized in Income on Derivatives (pre-tax)	(2)
Other contracts | Other | Foreign exchange forward contracts
Derivative Instruments, Gain (Loss) [Line Items]
Recognized in Income on Derivatives (pre-tax)	$ 2