Investment Income (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net Investment Income
Investment income, unrealized gains (losses)	$ 161,489	$ 99,634
Investment income, realized gains (losses)	33,158	37,129
Investment income	194,647	136,763	$ 0
Investments in publicly traded companies
Net Investment Income
Investment income, unrealized gains (losses)	130,802	27,944
Investment income, realized gains (losses)	0	0
Investment income	130,802	27,944
Investments in privately held entities that report NAV
Net Investment Income
Investment income, unrealized gains (losses)	49,440	22,389
Investment income, realized gains (losses)	0	0
Investment income	49,440	22,389
Investments in privately held entities that do not report NAV
Net Investment Income
Investment income, unrealized gains (losses)	4,378	64,112
Investment income, realized gains (losses)	(17,124)	(5,483)
Investment income	(12,746)	58,629
Total investments at fair value, held at period end
Net Investment Income
Investment income, unrealized gains (losses)	184,620	114,445
Investment income, realized gains (losses)	(17,124)	(5,483)
Investment income	167,496	108,962
Investment disposed and recognized during the period
Net Investment Income
Investment income, unrealized gains (losses)	0	0
Investment income, realized gains (losses)	27,151	27,801
Investment income	27,151	27,801
Investment disposed and previously recognized
Net Investment Income
Investment income, unrealized gains (losses)	(23,131)	(14,811)
Investment income, realized gains (losses)	23,131	14,811
Investment income	0	0
Total investment disposition during the period
Net Investment Income
Investment income, unrealized gains (losses)	(23,131)	(14,811)
Investment income, realized gains (losses)	50,282	42,612
Investment income	$ 27,151	$ 27,801

Amount of unrealized and realized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=116654751&loc=SL75117546-209714

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