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		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Derivative Instruments, Gain (Loss) [Line Items]
Recognized in Income on Derivatives (pre-tax)	$ 175	$ (5,894)	$ (553)	$ (1,480)
Commodity contracts | Principal transactions revenue, net | Futures
Derivative Instruments, Gain (Loss) [Line Items]
Recognized in Income on Derivatives (pre-tax)	172	(5,892)	(572)	(1,457)
Other contracts | Principal transactions revenue, net | TBAs
Derivative Instruments, Gain (Loss) [Line Items]
Recognized in Income on Derivatives (pre-tax)	$ 3	$ (2)	$ 19	1
Other contracts | Other | Foreign exchange forward contracts
Derivative Instruments, Gain (Loss) [Line Items]
Recognized in Income on Derivatives (pre-tax)				$ (24)