Consolidated Company-Sponsored Investment Funds - Narrative (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2021 USD ($) fund	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Derivative [Line Items]
Gains (losses) on derivative instruments	$ (11,414,000)	$ (30,913,000)	$ (9,078,000)	$ (1,347,000)
Cash collateral payable to trade counterparties	2,100,000		2,100,000		$ 400,000
Cash collateral received	4,400,000		4,400,000		6,400,000
Advisory fee receivables	156,157,000		156,157,000		148,746,000
VIEs
Derivative [Line Items]
Futures, forwards and swaps held	2,400,000		2,400,000		3,700,000
Gains (losses) on derivative instruments	(1,800,000)	1,000,000.0	(700,000)	(700,000)
Cash collateral payable to trade counterparties	442,000		442,000		513,000
Cash collateral received	989,000		989,000		4,201,000
VOEs
Derivative [Line Items]
Futures, forwards and swaps held	0		0		200,000
Gains (losses) on derivative instruments	(900,000)	$ (800,000)		$ (900,000)
Cash collateral payable to trade counterparties	0		0		0
Cash collateral received	0		0		$ 138,000
Variable Interest Entity, Not Primary Beneficiary
Derivative [Line Items]
Net assets	73,300,000,000		73,300,000,000
Maximum risk of loss in investment in VIEs	8,800,000		8,800,000
Advisory fee receivables	$ 77,600,000		77,600,000
Seed capital
Derivative [Line Items]
Number of deconsolidated funds | fund	2
Seed investment, deconsolidated amount	$ 86,100,000		$ 86,100,000