Derivative Instruments - Gain (Loss) From Derivative Instruments (Details)			3 Months Ended			9 Months Ended
	Jan. 29, 2020 USD ($) instrument	Oct. 09, 2019	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)
Derivative Instruments, Gain (Loss) [Line Items]
Derivative contract term	5 years	5 years
Not designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Trading income, net and Other, net			$ 84,129,000		$ (79,909,000)	$ 326,710,000	$ 35,657,000
Futures | Not designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Trading income, net and Other, net			(12,262,000)		(109,912,000)	11,440,000	45,698,000
Currency forwards | Not designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Trading income, net and Other, net			62,465,000		38,738,000	255,044,000	(6,304,000)
Options | Not designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Trading income, net and Other, net			35,343,000		(8,735,000)	61,643,000	(3,737,000)
Interest rate swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative contract term	5 years			5 years
Derivative, notional amount	$ 1,000,000,000			$ 525,000,000
Number of interest rate swaps | instrument	2
Interest rate swap | Not designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Trading income, net and Other, net			(1,417,000)		0	(1,417,000)	0
Interest rate swap | Derivative instruments designed as hedging instruments:
Derivative Instruments, Gain (Loss) [Line Items]
Other comprehensive income			$ 314,000		$ 0	$ (64,425,000)	$ 0