Marketable Securities and Equity Investments - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Summary of cash, cash equivalents and marketable securities
Cash	$ 2,700,000,000		$ 2,700,000,000		$ 2,800,000,000
Other-than-temporary declines in fair value of available-for-sale debt securities	0	$ 0	0	$ 0
Net unrealized gains	46,679,000	69,834,000	4,993,000	102,317,000
Weighted-average cost basis	69,418,000	$ 51,300,000	69,418,000	51,300,000	$ 51,427,000
Other Assets
Summary of cash, cash equivalents and marketable securities
Equity securities without readily determinable fair value, amount	$ 35,900,000		35,900,000
Publicly Traded Companies Sale
Summary of cash, cash equivalents and marketable securities
Proceeds received			$ 0	$ 149,600,000