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Investment Information - Narrative (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($) lots	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) lots	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($) lots
Narrative items:
Equity in net (loss) income of investment funds accounted for using the equity method	$ 105,398	$ 126,735	$ 299,270	$ 57,407
Equity securities, at fair value	$ 1,790,640		$ 1,790,640		$ 1,444,830
Continuous unrealized loss, qualitative disclosures:
Number of positions in an unrealized loss position (lots) | lots	3,910		3,910		2,320
Total number of positions (lots) | lots	10,020		10,020		11,180
Largest single loss	$ 2,500		$ 2,500		$ 900
Minimum
Narrative items:
Time lag for reporting			1 month
Maximum
Narrative items:
Time lag for reporting			3 months

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Disclosure regarding factors used to determine that the impairment of securities categorized as available for sale securitie.This item contains disclosure of the largest single loss position in a single lot as of the balance sheet date.

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Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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