Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	$ 773,626	$ 316,086
Gross Unrealized Gains	4	3
Gross Unrealized Losses	(458)	(546)
Fair Value	773,172	315,543
Cash equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	395,144	34,587
Fair Value	395,144	34,587
Cash equivalents [Member] \| Money market funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	319,668	23,110
Fair Value	319,668	23,110
Cash equivalents [Member] \| Time deposits [Member]
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	51,426	11,477
Fair Value	51,426	11,477
Cash equivalents [Member] \| Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	23,550
Fair Value	23,550
Cash equivalents [Member] \| Government and corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	500
Fair Value	500
Short-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	279,256	185,693
Gross Unrealized Gains	4	3
Gross Unrealized Losses	(264)	(108)
Fair Value	278,996	185,588
Short-term investments [Member] \| Time deposits [Member]
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	32,808	40,639
Fair Value	32,808	40,639
Short-term investments [Member] \| Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	87,916	22,325
Gross Unrealized Gains	2
Gross Unrealized Losses	(44)	(24)
Fair Value	87,874	22,301
Short-term investments [Member] \| Government and corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	158,532	122,729
Gross Unrealized Gains	2	3
Gross Unrealized Losses	(220)	(84)
Fair Value	158,314	122,648
Long-term investments [Member] \| Government and corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	99,226	95,806
Gross Unrealized Losses	(194)	(438)
Fair Value	$ 99,032	$ 95,368

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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