Investment Information - Narrative (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021 USD ($) lots	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) lots	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($) lots
Narrative items:
Investable assets	$ 30,200,000		$ 30,200,000
Equity in net (loss) income of investment funds accounted for using the equity method	122,186	$ (65,119)	193,872	$ (69,328)
Equity securities, at fair value	$ 1,693,552		$ 1,693,552		$ 1,444,830
Continuous unrealized loss, qualitative disclosures:
Number of positions in an unrealized loss position (lots) | lots	3,240		3,240		2,320
Total number of positions (lots) | lots	10,890		10,890		11,180
Largest single loss	$ 2,400		$ 2,400		$ 900
Consolidated Entity, Excluding Consolidated VIE
Narrative items:
Investable assets	27,300,000		27,300,000
Variable Interest Entity, Primary Beneficiary
Narrative items:
Investable assets	$ 2,900,000		$ 2,900,000
Minimum
Narrative items:
Time lag for reporting			1 month
Maximum
Narrative items:
Time lag for reporting			3 months