Fair Value of Financial Instruments - Auction rate securities and Contingent consideration (Details) - Auction rate securities - Significant Unobservable Inputs (Level 3) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Dec. 30, 2017
Weighted Average \| Discounted cash flow
Quantitative information for Level 3 Fair Value Measurements Assets
Estimated yield (as a percent)	2.22%
Expected holding period	10 years
Estimated discount rate (as a percent)	3.63%
Assets and liabilities measured at fair value on recurring basis
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value balance at the end of the period	$ 5,609	$ 5,681

Represents the estimated interest rates, used as an input to measure fair value.

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- Definition

Represents the expected holding period, used as an input to measure fair value.

+ References

No definition available.

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- Definition

Represents the liquidity discount, used as an input to measure fair value.

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No definition available.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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