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Marketable Securities and Equity Investments - Additional Information (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Summary of cash, cash equivalents and marketable securities
Cash	$ 2,300,000,000		$ 2,300,000,000		$ 2,300,000,000
Other-than-temporary declines in fair value of available-for-sale debt securities	0	$ 0	0	$ 0
Fair value	219,327,000		219,327,000		282,084,000
Unrealized gain (loss)	85,500,000	$ 56,500,000	35,200,000	100,100,000
Equity securities, cost basis	67,054,000		67,054,000		113,829,000
Other Assets
Summary of cash, cash equivalents and marketable securities
Equity securities without readily determinable fair value, amount	46,600,000		46,600,000
Corporate Equity Securities
Summary of cash, cash equivalents and marketable securities
Fair value	219,300,000		219,300,000		$ 282,100,000
Publically Traded Companies
Summary of cash, cash equivalents and marketable securities
Proceeds from sale and maturity of marketable securities			127,900,000	$ 0
Equity securities, cost basis	$ 46,800,000		$ 46,800,000