Note 1 - Summary of Significant Accounting Policies - Reported Share-based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 24, 2017	Jun. 25, 2016	Jun. 24, 2017	Jun. 25, 2016
Allocated share-based compensation	$ 1,759	$ 1,796	$ 3,476	$ 3,533
Income tax benefit	(249)	(73)	(322)	(113)
Total share-based compensation, net	1,510	1,723	3,154	3,420
Cost of Sales [Member]
Allocated share-based compensation	121	115	204	208
Research and Development Expense [Member]
Allocated share-based compensation	262	334	578	628
Selling, General and Administrative Expenses [Member]
Allocated share-based compensation	$ 1,376	$ 1,347	$ 2,694	$ 2,697

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.F)
-URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5047-113901

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(i)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration