Marketable Securities and Equity Investments - Summary of Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2020	Dec. 31, 2019
Total marketable debt securities
Fair Value	$ 2,199,419	$ 1,243,469
Corporate equity securities
Amortized Cost	87,096	113,829
Gross Unrealized Gains	78,082	168,255
Gross Unrealized Losses	0	0
Fair Value	165,178	282,084
Amortized Cost	519,163	530,216
Gross Unrealized Gains	78,837	168,811
Gross Unrealized Losses	(1,016)	(55)
Fair Value	596,984	698,972
Cash equivalents
Total marketable debt securities
Amortized Cost	1,767,613	826,579
Gross Unrealized Gains	4	3
Gross Unrealized Losses	(4)	(1)
Fair Value	1,767,613	826,581
Cash equivalents \| Money market funds
Total marketable debt securities
Amortized Cost	1,736,913	791,039
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	1,736,913	791,039
Cash equivalents \| Commercial paper
Total marketable debt securities
Amortized Cost	30,700	29,470
Gross Unrealized Gains	4	3
Gross Unrealized Losses	(4)	(1)
Fair Value	30,700	29,472
Cash equivalents \| Corporate debt securities
Total marketable debt securities
Amortized Cost		6,070
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Fair Value		6,070
Marketable securities
Total marketable debt securities
Amortized Cost	432,067	416,387
Gross Unrealized Gains	755	556
Gross Unrealized Losses	(1,016)	(55)
Fair Value	431,806	416,888
Marketable securities \| Government-sponsored enterprise securities
Total marketable debt securities
Amortized Cost	7,717	12,689
Gross Unrealized Gains	74	44
Gross Unrealized Losses	0	0
Fair Value	7,791	12,733
Marketable securities \| Corporate debt securities
Total marketable debt securities
Amortized Cost	305,808	301,458
Gross Unrealized Gains	255	391
Gross Unrealized Losses	(1,012)	(50)
Fair Value	305,051	301,799
Marketable securities \| Commercial paper
Total marketable debt securities
Amortized Cost	118,542	102,240
Gross Unrealized Gains	426	121
Gross Unrealized Losses	(4)	(5)
Fair Value	$ 118,964	$ 102,356

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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