Fair Value of Financial Instruments - Activity in Level 3 financial instruments (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 29, 2018	Sep. 29, 2018	Dec. 30, 2017
Recurring \| Significant Unobservable Inputs (Level 3) \| Auction rate securities
Fair value assets reconciliation of changes
Balance at the beginning of the period	$ 5,642	$ 5,681
Gain (loss) included in other comprehensive loss	108	69
Balance at the end of the period	5,750	5,750
Convertible Senior Notes
Fair value liabilities reconciliation of changes
Fair value of debt	$ 456,300	$ 456,300	$ 466,200

Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13433-108611

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

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- Definition

Amount of gain (loss) recognized in other comprehensive income (loss) for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
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- Definition

Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

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-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
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-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

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