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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Fair value as of the balance sheet date of all foreign currency derivatives designated as cash flow hedging instruments.

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Amount of investment in marketable security.

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The cash outflow associated with the purchase of all investments (debt, security, other) during the period.

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Fair Value Measurements (Details) - USD ($) $ in Thousands	9 Months Ended
Fair Value Measurements (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Fair value of financial assets and liabilities
Payments to Acquire Investments	$ 60,490	$ 0
Recurring basis
Financial instruments carried at fair value (asset position):
Total financial assets	1,711,766		$ 1,108,253
Financial instruments carried at fair value (liability position):
Total financial liabilities	(571)		(14,508)
Recurring basis \| Level 1
Financial instruments carried at fair value (asset position):
Total financial assets	1,298,184		704,753
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	413,582		403,500
Financial instruments carried at fair value (liability position):
Total financial liabilities	(571)		(14,508)
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	0		0
Prepaid expenses and other current assets \| Foreign currency forward contracts \| Recurring basis
Financial instruments carried at fair value (asset position):
Foreign currency forward contracts	13,903		13
Prepaid expenses and other current assets \| Foreign currency forward contracts \| Recurring basis \| Level 1
Financial instruments carried at fair value (asset position):
Foreign currency forward contracts	0		0
Prepaid expenses and other current assets \| Foreign currency forward contracts \| Recurring basis \| Level 2
Financial instruments carried at fair value (asset position):
Foreign currency forward contracts	13,903		13
Prepaid expenses and other current assets \| Foreign currency forward contracts \| Recurring basis \| Level 3
Financial instruments carried at fair value (asset position):
Foreign currency forward contracts	0		0
Other assets \| Foreign currency forward contracts \| Recurring basis
Financial instruments carried at fair value (asset position):
Foreign currency forward contracts	713
Other assets \| Foreign currency forward contracts \| Recurring basis \| Level 1
Financial instruments carried at fair value (asset position):
Foreign currency forward contracts	0
Other assets \| Foreign currency forward contracts \| Recurring basis \| Level 2
Financial instruments carried at fair value (asset position):
Foreign currency forward contracts	713
Other assets \| Foreign currency forward contracts \| Recurring basis \| Level 3
Financial instruments carried at fair value (asset position):
Foreign currency forward contracts	0
Other liabilities, current portion \| Foreign currency forward contracts \| Recurring basis
Financial instruments carried at fair value (liability position):
Derivative liability current	(505)		(13,642)
Other liabilities, current portion \| Foreign currency forward contracts \| Recurring basis \| Level 1
Financial instruments carried at fair value (liability position):
Derivative liability current	0		0
Other liabilities, current portion \| Foreign currency forward contracts \| Recurring basis \| Level 2
Financial instruments carried at fair value (liability position):
Derivative liability current	(505)		(13,642)
Other liabilities, current portion \| Foreign currency forward contracts \| Recurring basis \| Level 3
Financial instruments carried at fair value (liability position):
Derivative liability current	0		0
Other liabilities, excluding current portion \| Foreign currency forward contracts \| Recurring basis
Financial instruments carried at fair value (liability position):
Derivative liability, noncurrent	(66)		(866)
Other liabilities, excluding current portion \| Foreign currency forward contracts \| Recurring basis \| Level 1
Financial instruments carried at fair value (liability position):
Derivative liability, noncurrent	0		0
Other liabilities, excluding current portion \| Foreign currency forward contracts \| Recurring basis \| Level 2
Financial instruments carried at fair value (liability position):
Derivative liability, noncurrent	(66)		(866)
Other liabilities, excluding current portion \| Foreign currency forward contracts \| Recurring basis \| Level 3
Financial instruments carried at fair value (liability position):
Derivative liability, noncurrent	0		0
Money market funds \| Recurring basis
Financial instruments carried at fair value (asset position):
Cash equivalents	1,070,166		614,951
Money market funds \| Recurring basis \| Level 1
Financial instruments carried at fair value (asset position):
Cash equivalents	1,070,166		614,951
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
US Treasury Securities \| Recurring basis
Financial instruments carried at fair value (asset position):
Cash equivalents	5,979
Marketable securities	6,043
US Treasury Securities \| Recurring basis \| Level 1
Financial instruments carried at fair value (asset position):
Cash equivalents	5,979
Marketable securities	6,043
US Treasury Securities \| Recurring basis \| Level 2
Financial instruments carried at fair value (asset position):
Cash equivalents	0
Marketable securities	0
US Treasury Securities \| Recurring basis \| Level 3
Financial instruments carried at fair value (asset position):
Cash equivalents	0
Marketable securities	0
Government-sponsored enterprise securities \| Recurring basis
Financial instruments carried at fair value (asset position):
Cash equivalents	2,498		12,678
Marketable securities	6,462		2,303
Government-sponsored enterprise securities \| Recurring basis \| Level 1
Financial instruments carried at fair value (asset position):
Cash equivalents	2,498		12,678
Marketable securities	6,462		2,303
Government-sponsored enterprise securities \| Recurring basis \| Level 2
Financial instruments carried at fair value (asset position):
Cash equivalents	0		0
Marketable securities	0		0
Government-sponsored enterprise securities \| Recurring basis \| Level 3
Financial instruments carried at fair value (asset position):
Cash equivalents	0		0
Marketable securities	0		0
Corporate debt securities \| Recurring basis
Financial instruments carried at fair value (asset position):
Cash equivalents	7,572
Marketable securities	218,082		265,867
Corporate debt securities \| Recurring basis \| Level 1
Financial instruments carried at fair value (asset position):
Cash equivalents	0
Marketable securities	0		0
Corporate debt securities \| Recurring basis \| Level 2
Financial instruments carried at fair value (asset position):
Cash equivalents	7,572
Marketable securities	218,082		265,867
Corporate debt securities \| Recurring basis \| Level 3
Financial instruments carried at fair value (asset position):
Cash equivalents	0
Marketable securities	0		0
Commercial paper \| Recurring basis
Financial instruments carried at fair value (asset position):
Cash equivalents	33,352		57,357
Marketable securities	139,960		80,263
Commercial paper \| Recurring basis \| Level 1
Financial instruments carried at fair value (asset position):
Cash equivalents	0		0
Marketable securities	0		0
Commercial paper \| Recurring basis \| Level 2
Financial instruments carried at fair value (asset position):
Cash equivalents	33,352		57,357
Marketable securities	139,960		80,263
Commercial paper \| Recurring basis \| Level 3
Financial instruments carried at fair value (asset position):
Cash equivalents	0		0
Marketable securities	0		0
Corporate equity securities \| Recurring basis
Financial instruments carried at fair value (asset position):
Marketable securities	207,036		74,821
Corporate equity securities \| Recurring basis \| Level 1
Financial instruments carried at fair value (asset position):
Marketable securities	207,036		74,821
Corporate equity securities \| Recurring basis \| Level 2
Financial instruments carried at fair value (asset position):
Marketable securities	0		0
Corporate equity securities \| Recurring basis \| Level 3
Financial instruments carried at fair value (asset position):
Marketable securities	0		$ 0
Variable Interest Entity, Primary Beneficiary \| Level 1
Financial instruments carried at fair value (liability position):
Cash and cash equivalents	5,000
CRISPR
Fair value of financial assets and liabilities
Payments to Acquire Investments	$ 46,900