Fair Value Measurements - Financial Assets and Liabilities Subject to Fair Value Measurements (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Financial instruments carried at fair value (asset position):
Marketable securities:	$ 3,615,982	$ 1,243,469
Financial instruments carried at fair value (liability position):
Long-term contingent consideration	(189,600)	(176,500)
Recurring basis
Financial instruments carried at fair value (asset position):
Total financial assets	3,811,763	1,535,278
Financial instruments carried at fair value (liability position):
Total financial liabilities	(253,067)	(183,854)
Recurring basis \| Level 1
Financial instruments carried at fair value (asset position):
Total financial assets	3,236,766	1,065,569
Financial instruments carried at fair value (liability position):
Total financial liabilities	0	0
Recurring basis \| Level 2
Financial instruments carried at fair value (asset position):
Total financial assets	574,997	469,709
Financial instruments carried at fair value (liability position):
Total financial liabilities	(63,467)	(7,354)
Recurring basis \| Level 3
Financial instruments carried at fair value (asset position):
Total financial assets	0	0
Financial instruments carried at fair value (liability position):
Total financial liabilities	(189,600)	(176,500)
Corporate equity securities \| Recurring basis
Financial instruments carried at fair value (asset position):
Marketable securities:	195,781	282,084
Corporate equity securities \| Recurring basis \| Level 1
Financial instruments carried at fair value (asset position):
Marketable securities:	15,650	261,797
Corporate equity securities \| Recurring basis \| Level 2
Financial instruments carried at fair value (asset position):
Marketable securities:	180,131	20,287
Corporate equity securities \| Recurring basis \| Level 3
Financial instruments carried at fair value (asset position):
Marketable securities:	0	0
Government-sponsored enterprise securities \| Recurring basis
Financial instruments carried at fair value (asset position):
Marketable securities:	80,063	12,733
Government-sponsored enterprise securities \| Recurring basis \| Level 1
Financial instruments carried at fair value (asset position):
Marketable securities:	80,063	12,733
Government-sponsored enterprise securities \| Recurring basis \| Level 2
Financial instruments carried at fair value (asset position):
Marketable securities:	0	0
Government-sponsored enterprise securities \| Recurring basis \| Level 3
Financial instruments carried at fair value (asset position):
Marketable securities:	0	0
Corporate debt securities \| Recurring basis
Financial instruments carried at fair value (asset position):
Marketable securities:	231,598	301,799
Corporate debt securities \| Recurring basis \| Level 1
Financial instruments carried at fair value (asset position):
Marketable securities:	0	0
Corporate debt securities \| Recurring basis \| Level 2
Financial instruments carried at fair value (asset position):
Marketable securities:	231,598	301,799
Corporate debt securities \| Recurring basis \| Level 3
Financial instruments carried at fair value (asset position):
Marketable securities:	0	0
Commercial paper \| Recurring basis
Financial instruments carried at fair value (asset position):
Marketable securities:	163,268	102,356
Commercial paper \| Recurring basis \| Level 1
Financial instruments carried at fair value (asset position):
Marketable securities:	0	0
Commercial paper \| Recurring basis \| Level 2
Financial instruments carried at fair value (asset position):
Marketable securities:	163,268	102,356
Commercial paper \| Recurring basis \| Level 3
Financial instruments carried at fair value (asset position):
Marketable securities:	0	0
Money market funds \| Recurring basis
Financial instruments carried at fair value (asset position):
Cash equivalents:	3,141,053	791,039
Money market funds \| Recurring basis \| Level 1
Financial instruments carried at fair value (asset position):
Cash equivalents:	3,141,053	791,039
Money market funds \| Recurring basis \| Level 2
Financial instruments carried at fair value (asset position):
Cash equivalents:	0	0
Money market funds \| Recurring basis \| Level 3
Financial instruments carried at fair value (asset position):
Cash equivalents:	0	0
Corporate debt securities \| Recurring basis
Financial instruments carried at fair value (asset position):
Cash equivalents:	0	6,070
Corporate debt securities \| Recurring basis \| Level 1
Financial instruments carried at fair value (asset position):
Cash equivalents:	0	0
Corporate debt securities \| Recurring basis \| Level 2
Financial instruments carried at fair value (asset position):
Cash equivalents:	0	6,070
Corporate debt securities \| Recurring basis \| Level 3
Financial instruments carried at fair value (asset position):
Cash equivalents:	0	0
Commercial paper \| Recurring basis
Financial instruments carried at fair value (asset position):
Cash equivalents:	0	29,472
Commercial paper \| Recurring basis \| Level 1
Financial instruments carried at fair value (asset position):
Cash equivalents:	0	0
Commercial paper \| Recurring basis \| Level 2
Financial instruments carried at fair value (asset position):
Cash equivalents:	0	29,472
Commercial paper \| Recurring basis \| Level 3
Financial instruments carried at fair value (asset position):
Cash equivalents:	0	0
Prepaid expenses and other current assets \| Foreign currency forward contracts \| Recurring basis
Financial instruments carried at fair value (asset position):
Derivative Asset	0	9,725
Prepaid expenses and other current assets \| Foreign currency forward contracts \| Recurring basis \| Level 1
Financial instruments carried at fair value (asset position):
Derivative Asset	0	0
Prepaid expenses and other current assets \| Foreign currency forward contracts \| Recurring basis \| Level 2
Financial instruments carried at fair value (asset position):
Derivative Asset	0	9,725
Prepaid expenses and other current assets \| Foreign currency forward contracts \| Recurring basis \| Level 3
Financial instruments carried at fair value (asset position):
Derivative Asset	0	0
Other current liabilities \| Recurring basis
Financial instruments carried at fair value (liability position):
Long-term contingent consideration	(189,600)	(176,500)
Other current liabilities \| Recurring basis \| Level 1
Financial instruments carried at fair value (liability position):
Long-term contingent consideration	0	0
Other current liabilities \| Recurring basis \| Level 2
Financial instruments carried at fair value (liability position):
Long-term contingent consideration	0	0
Other current liabilities \| Recurring basis \| Level 3
Financial instruments carried at fair value (liability position):
Long-term contingent consideration	(189,600)	(176,500)
Other current liabilities \| Foreign currency forward contracts \| Recurring basis
Financial instruments carried at fair value (liability position):
Derivative Liability	(59,184)	(5,533)
Other current liabilities \| Foreign currency forward contracts \| Recurring basis \| Level 1
Financial instruments carried at fair value (liability position):
Derivative Liability	0	0
Other current liabilities \| Foreign currency forward contracts \| Recurring basis \| Level 2
Financial instruments carried at fair value (liability position):
Derivative Liability	(59,184)	(5,533)
Other current liabilities \| Foreign currency forward contracts \| Recurring basis \| Level 3
Financial instruments carried at fair value (liability position):
Derivative Liability	0	0
Other long-term liabilities \| Foreign currency forward contracts \| Recurring basis
Financial instruments carried at fair value (liability position):
Derivative Liability	(4,283)	(1,821)
Other long-term liabilities \| Foreign currency forward contracts \| Recurring basis \| Level 1
Financial instruments carried at fair value (liability position):
Derivative Liability	0	0
Other long-term liabilities \| Foreign currency forward contracts \| Recurring basis \| Level 2
Financial instruments carried at fair value (liability position):
Derivative Liability	(4,283)	(1,821)
Other long-term liabilities \| Foreign currency forward contracts \| Recurring basis \| Level 3
Financial instruments carried at fair value (liability position):
Derivative Liability	$ 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 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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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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