Fair value measurements - Fair Value Amounts of Derivative Instruments and their Effect on Statement of Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Derivative Instruments, Gain (Loss) [Line Items]
Recognized in Income (pre-tax) Gain (Loss)	$ 2,933	$ 4,684
Commodity contracts | Principal transactions revenue | Futures
Derivative Instruments, Gain (Loss) [Line Items]
Recognized in Income (pre-tax) Gain (Loss)	2,842	4,652
Other contracts | Principal transactions revenue | TBAs
Derivative Instruments, Gain (Loss) [Line Items]
Recognized in Income (pre-tax) Gain (Loss)	26	60
Other contracts | Other revenue | Foreign exchange forward contracts
Derivative Instruments, Gain (Loss) [Line Items]
Recognized in Income (pre-tax) Gain (Loss)	$ 65	$ (28)