Consolidated Company-Sponsored Investment Funds (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Dec. 31, 2019
Derivative [Line Items]
Gains (losses) on derivative instruments	$ (14,090)	$ (115)	$ (15,437)	$ (28,997)
Cash collateral payable to trade counterparties	1,000		1,000			$ 300
Cash collateral received	3,600		3,600			4,300
Maximum risk of loss in investment in VIEs	6,700		6,700
Variable Interest Entity, Not Primary Beneficiary
Derivative [Line Items]
Net assets	68,900,000		68,900,000
VIEs
Derivative [Line Items]
Futures, forwards and swaps held	3,100		3,100			300
Gains (losses) on derivative instruments	600	600	(100)	3,300
Cash Collateral payable to trade counterparties including amounts that exceed fair value of assets	300		300
Cash collateral payable to trade counterparties	301		301			1,631
Cash collateral received	3,700		3,700			3,200
VOEs
Derivative [Line Items]
Futures, forwards and swaps held	2,400		2,400			700
Gains (losses) on derivative instruments	(1,300)	$ 1,000	(2,200)	$ 500
Cash Collateral payable to trade counterparties including amounts that exceed fair value of assets	1,000		1,000
Cash collateral payable to trade counterparties	985		985			534
Cash collateral received	$ 1,500		$ 1,500			$ 1,200
Seed capital
Derivative [Line Items]
Seed investment, deconsolidated amount					$ 59,000