Marketable Securities and Equity Investments - Summary of Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Available-for-sale Debt Securities
Fair Value	$ 1,243,469	$ 1,648,745
Equity Securities, FV-NI and without Readily Determinable Fair Value [Abstract]
Amortized Cost	530,216	484,473
Gross Unrealized Gains	168,811	40,646
Gross Unrealized Losses	(55)	(7,011)
Fair Value	698,972	518,108
Money market funds
Summary of cash, cash equivalents and marketable securities
Amortized Cost	791,039	1,226,603
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	791,039	1,226,603
Corporate debt securities
Summary of cash, cash equivalents and marketable securities
Amortized Cost	6,070
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	6,070
Available-for-sale Debt Securities
Amortized Cost	301,458	234,088
Gross Unrealized Gains	391	27
Gross Unrealized Losses	(50)	(450)
Fair Value	301,799	233,665
U.S. Treasury securities
Summary of cash, cash equivalents and marketable securities
Amortized Cost		5,967
Gross Unrealized Gains		0
Gross Unrealized Losses		(1)
Fair Value		5,966
Government-sponsored enterprise securities
Summary of cash, cash equivalents and marketable securities
Amortized Cost		7,124
Gross Unrealized Gains		0
Gross Unrealized Losses		(1)
Fair Value		7,123
Commercial paper
Summary of cash, cash equivalents and marketable securities
Amortized Cost	29,470	58,271
Gross Unrealized Gains	3	0
Gross Unrealized Losses	(1)	(3)
Fair Value	29,472	58,268
Cash Equivalents
Summary of cash, cash equivalents and marketable securities
Amortized Cost	826,579	1,297,965
Gross Unrealized Gains	3	0
Gross Unrealized Losses	(1)	(5)
Fair Value	826,581	1,297,960
Total marketable debt securities
Available-for-sale Debt Securities
Amortized Cost	416,387	351,316
Gross Unrealized Gains	556	27
Gross Unrealized Losses	(55)	(558)
Fair Value	416,888	350,785
U.S Treasury securities
Available-for-sale Debt Securities
Amortized Cost		6,026
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Fair Value		6,026
Government-sponsored enterprise securities
Available-for-sale Debt Securities
Amortized Cost	12,689	10,704
Gross Unrealized Gains	44	0
Gross Unrealized Losses	0	0
Fair Value	12,733	10,704
Commercial paper
Available-for-sale Debt Securities
Amortized Cost	102,240	100,498
Gross Unrealized Gains	121	0
Gross Unrealized Losses	(5)	(108)
Fair Value	102,356	100,390
Corporate equity securities
Equity Securities, FV-NI and without Readily Determinable Fair Value [Abstract]
Amortized Cost	113,829	133,157
Gross Unrealized Gains	168,255	40,619
Gross Unrealized Losses	0	(6,453)
Fair Value	$ 282,084	$ 167,323