- Short Term Investments (Details) - USD ($) $ in Thousands	Dec. 30, 2017	Dec. 31, 2016
Components of available for sale securities
Total short term investments, Cost	$ 37,767	$ 40,439
Total short term investments, Fair Market Value	37,225	39,930
Corporate and government bonds
Components of available for sale securities
Total short term investments, Cost	37,767	40,439
Total short term investments, Fair Market Value	$ 37,225	$ 39,930

Amount of investment in debt and equity securities categorized neither as trading securities nor held-to-maturity securities and intended be sold or mature one year or operating cycle, if longer.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=75030427&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26626-111562

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant