Fair Value Measurements - Financial Assets and Liabilities Subject to Fair Value Measurements (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financial instruments carried at fair value (liability positions):
Long-term contingent consideration	$ (189,100)	$ (176,500)
Recurring Basis
Financial instruments carried at fair value (asset positions):
Derivative asset current, foreign currency forward contracts	673	9,725
Total financial assets	3,929,009	1,535,278
Financial instruments carried at fair value (liability positions):
Derivative liability current, foreign currency forward contracts	(29,554)	(5,533)
Long-term contingent consideration	(189,100)	(176,500)
Derivative liability noncurrent, foreign currency forward contracts	(3,254)	(1,821)
Total financial liabilities	(221,908)	(183,854)
Recurring Basis \| Level 1
Financial instruments carried at fair value (asset positions):
Derivative asset current, foreign currency forward contracts	0	0
Total financial assets	3,437,789	1,065,569
Financial instruments carried at fair value (liability positions):
Derivative liability current, foreign currency forward contracts	0	0
Long-term contingent consideration	0	0
Derivative liability noncurrent, foreign currency forward contracts	0	0
Total financial liabilities	0	0
Recurring Basis \| Level 2
Financial instruments carried at fair value (asset positions):
Derivative asset current, foreign currency forward contracts	673	9,725
Total financial assets	491,220	469,709
Financial instruments carried at fair value (liability positions):
Derivative liability current, foreign currency forward contracts	(29,554)	(5,533)
Long-term contingent consideration	0	0
Derivative liability noncurrent, foreign currency forward contracts	(3,254)	(1,821)
Total financial liabilities	(32,808)	(7,354)
Recurring Basis \| Level 3
Financial instruments carried at fair value (asset positions):
Derivative asset current, foreign currency forward contracts	0	0
Total financial assets	0	0
Financial instruments carried at fair value (liability positions):
Derivative liability current, foreign currency forward contracts	0	0
Long-term contingent consideration	(189,100)	(176,500)
Derivative liability noncurrent, foreign currency forward contracts	0	0
Total financial liabilities	(189,100)	(176,500)
Recurring Basis \| Money market funds
Financial instruments carried at fair value (asset positions):
Cash and cash equivalents	3,130,364	791,039
Recurring Basis \| Money market funds \| Level 1
Financial instruments carried at fair value (asset positions):
Cash and cash equivalents	3,130,364	791,039
Recurring Basis \| Money market funds \| Level 2
Financial instruments carried at fair value (asset positions):
Cash and cash equivalents	0	0
Recurring Basis \| Money market funds \| Level 3
Financial instruments carried at fair value (asset positions):
Cash and cash equivalents	0	0
Recurring Basis \| Corporate equity securities
Financial instruments carried at fair value (asset positions):
Marketable securities	312,682	282,084
Recurring Basis \| Corporate equity securities \| Level 1
Financial instruments carried at fair value (asset positions):
Marketable securities	216,142	261,797
Recurring Basis \| Corporate equity securities \| Level 2
Financial instruments carried at fair value (asset positions):
Marketable securities	96,540	20,287
Recurring Basis \| Corporate equity securities \| Level 3
Financial instruments carried at fair value (asset positions):
Marketable securities	0	0
Recurring Basis \| Government-sponsored enterprise securities
Financial instruments carried at fair value (asset positions):
Marketable securities	91,283	12,733
Recurring Basis \| Government-sponsored enterprise securities \| Level 1
Financial instruments carried at fair value (asset positions):
Marketable securities	91,283	12,733
Recurring Basis \| Government-sponsored enterprise securities \| Level 2
Financial instruments carried at fair value (asset positions):
Marketable securities	0	0
Recurring Basis \| Government-sponsored enterprise securities \| Level 3
Financial instruments carried at fair value (asset positions):
Marketable securities	0	0
Recurring Basis \| Corporate debt securities
Financial instruments carried at fair value (asset positions):
Cash and cash equivalents	0	6,070
Marketable securities	276,610	301,799
Recurring Basis \| Corporate debt securities \| Level 1
Financial instruments carried at fair value (asset positions):
Cash and cash equivalents	0	0
Marketable securities	0	0
Recurring Basis \| Corporate debt securities \| Level 2
Financial instruments carried at fair value (asset positions):
Cash and cash equivalents	0	6,070
Marketable securities	276,610	301,799
Recurring Basis \| Corporate debt securities \| Level 3
Financial instruments carried at fair value (asset positions):
Cash and cash equivalents	0	0
Marketable securities	0	0
Recurring Basis \| Commercial paper
Financial instruments carried at fair value (asset positions):
Cash and cash equivalents	5,001	29,472
Marketable securities	112,396	102,356
Recurring Basis \| Commercial paper \| Level 1
Financial instruments carried at fair value (asset positions):
Cash and cash equivalents	0	0
Marketable securities	0	0
Recurring Basis \| Commercial paper \| Level 2
Financial instruments carried at fair value (asset positions):
Cash and cash equivalents	5,001	29,472
Marketable securities	112,396	102,356
Recurring Basis \| Commercial paper \| Level 3
Financial instruments carried at fair value (asset positions):
Cash and cash equivalents	0	0
Marketable securities	$ 0	$ 0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of liability recognized arising from contingent consideration in a business combination, expected to be settled beyond one year or the normal operating cycle, if longer.

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Amount of investment in marketable security.

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