Investments (Details) - USD ($) $ in Thousands	Jul. 01, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	$ 456,312	$ 316,086
Gross Unrealized Gains	4	3
Gross Unrealized Losses	(456)	(546)
Fair Value	455,860	315,543
Cash equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	180,142	34,587
Fair Value	180,142	34,587
Cash equivalents [Member] \| Money market funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	58,559	23,110
Fair Value	58,559	23,110
Cash equivalents [Member] \| Time deposits [Member]
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	17,383	11,477
Fair Value	17,383	11,477
Cash equivalents [Member] \| Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	96,200
Fair Value	96,200
Cash equivalents [Member] \| Government and corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	8,000
Fair Value	8,000
Short-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	176,750	185,693
Gross Unrealized Gains	3	3
Gross Unrealized Losses	(190)	(108)
Fair Value	176,563	185,588
Short-term investments [Member] \| Time deposits [Member]
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	20,863	40,639
Fair Value	20,863	40,639
Short-term investments [Member] \| Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	35,925	22,325
Gross Unrealized Losses	(36)	(24)
Fair Value	35,889	22,301
Short-term investments [Member] \| Government and corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	119,962	122,729
Gross Unrealized Gains	3	3
Gross Unrealized Losses	(154)	(84)
Fair Value	119,811	122,648
Long-term investments [Member] \| Government and corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	99,420	95,806
Gross Unrealized Gains	1
Gross Unrealized Losses	(266)	(438)
Fair Value	$ 99,155	$ 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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