Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 30, 2017
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	$ 601,849	$ 781,484
Gross Unrealized Gains		2
Gross Unrealized Losses	(1,979)	(1,642)
Available-for-sale Securities	599,870	779,844
Cash equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	120,776	160,548
Available-for-sale Securities	120,776	160,548
Cash equivalents [Member] \| Money market funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	42,195	99,472
Available-for-sale Securities	42,195	99,472
Cash equivalents [Member] \| Time deposits [Member]
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	78,581	60,226
Available-for-sale Securities	78,581	60,226
Cash equivalents [Member] \| Government and corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost		850
Available-for-sale Securities		850
Short-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	375,822	435,458
Gross Unrealized Gains		2
Gross Unrealized Losses	(1,226)	(616)
Available-for-sale Securities	374,596	434,844
Short-term investments [Member] \| Time deposits [Member]
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	28,988	40,186
Available-for-sale Securities	28,988	40,186
Short-term investments [Member] \| Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	77,950	147,646
Gross Unrealized Gains		2
Gross Unrealized Losses	(98)	(139)
Available-for-sale Securities	77,852	147,509
Short-term investments [Member] \| Government and corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	268,884	247,626
Gross Unrealized Losses	(1,128)	(477)
Available-for-sale Securities	267,756	247,149
Long-term investments [Member] \| Government and corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	105,251	185,478
Gross Unrealized Losses	(753)	(1,026)
Available-for-sale Securities	$ 104,498	$ 184,452

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
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-URI http://asc.fasb.org/extlink&oid=75030427&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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