Fair Value Measurements - Financial Assets and Liabilities Subject to Fair Value Measurements (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Financial instruments carried at fair value (liability positions):
Long-term contingent consideration	$ (187,300)	$ (176,500)
Recurring Basis
Financial instruments carried at fair value (asset positions):
Derivative asset current, foreign currency forward contracts	8,054	9,725
Derivative asset noncurrent, foreign currency forward contracts	44	0
Total financial assets	3,202,190	1,535,278
Financial instruments carried at fair value (liability positions):
Derivative liability current, foreign currency forward contracts	(4,871)	(5,533)
Long-term contingent consideration	(187,300)	(176,500)
Derivative liability noncurrent, foreign currency forward contracts	(1,462)	(1,821)
Total financial liabilities	(193,633)	(183,854)
Recurring Basis \| Level 1
Financial instruments carried at fair value (asset positions):
Derivative asset current, foreign currency forward contracts	0	0
Derivative asset noncurrent, foreign currency forward contracts	0	0
Total financial assets	2,697,180	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	8,054	9,725
Derivative asset noncurrent, foreign currency forward contracts	44	0
Total financial assets	505,010	469,709
Financial instruments carried at fair value (liability positions):
Derivative liability current, foreign currency forward contracts	(4,871)	(5,533)
Long-term contingent consideration	0	0
Derivative liability noncurrent, foreign currency forward contracts	(1,462)	(1,821)
Total financial liabilities	(6,333)	(7,354)
Recurring Basis \| Level 3
Financial instruments carried at fair value (asset positions):
Derivative asset current, foreign currency forward contracts	0	0
Derivative asset noncurrent, 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	(187,300)	(176,500)
Derivative liability noncurrent, foreign currency forward contracts	0	0
Total financial liabilities	(187,300)	(176,500)
Recurring Basis \| Money market funds
Financial instruments carried at fair value (asset positions):
Cash and cash equivalents	2,476,713	791,039
Recurring Basis \| Money market funds \| Level 1
Financial instruments carried at fair value (asset positions):
Cash and cash equivalents	2,476,713	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	219,327	282,084
Recurring Basis \| Corporate equity securities \| Level 1
Financial instruments carried at fair value (asset positions):
Marketable securities	209,214	261,797
Recurring Basis \| Corporate equity securities \| Level 2
Financial instruments carried at fair value (asset positions):
Marketable securities	10,113	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	11,253	12,733
Recurring Basis \| Government-sponsored enterprise securities \| Level 1
Financial instruments carried at fair value (asset positions):
Marketable securities	11,253	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	4,835	6,070
Marketable securities	293,976	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	4,835	6,070
Marketable securities	293,976	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	93,107	29,472
Marketable securities	94,881	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	93,107	29,472
Marketable securities	94,881	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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Amount of investment in marketable security.

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