Consolidation - Narrative (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Variable Interest Entities [Line Items]
Fee waivers	$ 184,900,000	$ 101,700,000	$ 315,400,000	$ 200,500,000
VIE
Variable Interest Entities [Line Items]
Investment redeemed	6,000,000.0
AUM	272,700,000		272,700,000		$ 9,600,000,000
VIE | Other Long-Term Assets
Variable Interest Entities [Line Items]
Maximum risk of loss from non-consolidated VIEs	5,000,000.0		5,000,000.0
VIE | Cash and Cash Equivalents
Variable Interest Entities [Line Items]
Maximum risk of loss from non-consolidated VIEs					111,900,000
VIE | Receivables - Affiliates
Variable Interest Entities [Line Items]
Maximum risk of loss from non-consolidated VIEs	300,000		300,000		$ 15,400,000
Financial Support, Fee Waivers
Variable Interest Entities [Line Items]
Money market funds which meet the scope exception of the consolidation guidance	141,600,000	73,700,000	241,700,000	141,800,000
Financial Support, Capital Contributions
Variable Interest Entities [Line Items]
Money market funds which meet the scope exception of the consolidation guidance	$ 0	$ 0	$ 0	$ 0