Fair Value Measurements - Schedule of Level Three Investment Reconciliation (Details) - USD ($)	3 Months Ended			6 Months Ended	9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2018	Jun. 30, 2019	Sep. 30, 2019	Sep. 30, 2018
Consolidated Funds’ other investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
At beginning of the period	$ 0		$ 26,500,000	$ 0	$ 0	$ 0
Additions (redemptions)	0		0		0	0
Transfers in (out) of Level 3	0		0		0	26,500,000
Change in recognition based on adoption of ASU 2016-01	0		(26,500,000)		0	(26,500,000)
Total net fair value losses recognized in net income	0		0		0	0
Total Level III financial assets	0	$ 0	0	0	0	0
Investments in unconsolidated Funds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
At beginning of the period	3,000,000.0		5,200,000	3,000,000.0	3,000,000.0	0
Additions (redemptions)	100,000		(300,000)		100,000	(300,000)
Transfers in (out) of Level 3		0	0	0		0
Change in recognition based on adoption of ASU 2016-01	0		0		0	6,400,000
Total net fair value losses recognized in net income	(100,000)		(300,000)		(100,000)	(1,500,000)
Total Level III financial assets	$ 3,000,000.0	$ 3,000,000.0	$ 4,600,000	$ 3,000,000.0	$ 3,000,000.0	$ 4,600,000