Consolidated Company-Sponsored Investment Funds (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Derivative [Line Items]
Gains (losses) on derivative instruments	$ (30,913)	$ (9,117)	$ (1,347)	$ (28,882)
Cash collateral payable to trade counterparties	800		800		$ 300
Cash collateral received	5,900		5,900		4,300
Maximum risk of loss in investment in VIEs	12,500		12,500
VIEs
Derivative [Line Items]
Futures, forwards and swaps held	(3,000)		(3,000)		300
Gains (losses) on derivative instruments	1,000	1,600	(700)	2,700
Cash Collateral payable to trade counterparties including amounts that exceed fair value of assets	300		300
Cash collateral payable to trade counterparties	270		270		1,631
Cash collateral received	3,800		3,800		3,200
VOEs
Derivative [Line Items]
Futures, forwards and swaps held	(1,000)		(1,000)		700
Gains (losses) on derivative instruments	(800)	$ 600	(900)	$ 500
Cash Collateral payable to trade counterparties including amounts that exceed fair value of assets	900		900
Cash collateral payable to trade counterparties	698		698		534
Cash collateral received	2,000		2,000		$ 1,200
Seed capital
Derivative [Line Items]
Seed investment, deconsolidated amount	$ 59,000		$ 59,000