Fair value measurements - Fair Value Amounts of Derivative Instruments and their Effect on Statement of Operations (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Derivative Instruments, Gain (Loss) [Line Items]
Recognized in Income on Derivatives (pre-tax) Gain (Loss)	$ 3,558	$ 1,302	$ 3,769	$ 3,555
Commodity contracts | Principal Transaction Revenue | Futures
Derivative Instruments, Gain (Loss) [Line Items]
Recognized in Income on Derivatives (pre-tax) Gain (Loss)	3,529	1,328	3,739	3,519
Other contracts | Principal Transaction Revenue | TBAs
Derivative Instruments, Gain (Loss) [Line Items]
Recognized in Income on Derivatives (pre-tax) Gain (Loss)	36	(6)	38	56
Other contracts | Other | Foreign exchange forward contracts
Derivative Instruments, Gain (Loss) [Line Items]
Recognized in Income on Derivatives (pre-tax) Gain (Loss)	$ (7)	$ (20)	$ (8)	$ (20)